Even in a noisy environment with fluctuations in pattern speed and encounters with the Sagittarius dwarf galaxy, a tree-ring structure arises in phase space measurements of the Milky Way’s galactic bar.

The post Tree-Ring Structure of Galactic Bar Resonance in N-Body Simulations appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Tracing Black Hole and Galaxy Growth Across Environments Since Cosmic Noon
Authors: Emma Jane Weller et al.
First Author’s Institution: Yale University
Status: Published in ApJ

They say you can’t choose your hometown, but it still ends up shaping who you become. Turns out the same is true for black holes. The galaxy a black hole grows up in will have a major impact on how it will live out the rest of its life. Similarly, the black hole can leave a lasting impression on its galaxy!

Astronomers have long known that a galaxy’s stellar mass (the combined mass of all its stars) tracks pretty tightly with the mass of the black hole sitting at its centre: bigger galaxy, bigger black hole. This is one pillar of the idea that galaxies and their central black holes coevolve; that is, their life stories are tangled up with one another from early on. But ever since JWST started spotting suspiciously large black holes in the early universe, astronomers have been debating whether this relationship holds steady across cosmic time, or whether the rules were different when the universe and everything in it was younger.

Not Everyone Stays in the Town Centre

Most previous studies of the relationship between black holes and their galaxies have focused only on the central black hole: the biggest, most famous resident of a galaxy, sitting right downtown at its centre. That’s a reasonable place to start, since the central black hole is usually the most massive one around and tends to dominate the story. But this article’s authors wanted to know what happens to everyone else in town, too!

That includes satellite black holes, which are the central black holes of smaller “satellite” galaxies that orbit a bigger “primary” galaxy, a bit like a small town around a big city. It also includes a stranger, more recently discovered population: wandering black holes. These are the black hole equivalent of someone whose hometown got swallowed up by an expanding metropolis, and who never quite settled into their new surroundings.

Here’s how it happens: when a small satellite galaxy merges with a larger one, the satellite gets torn apart by tidal forces and its gas and stars are stripped away. However, its central black hole is often left behind, drifting through the new, much bigger galaxy on a wide orbit. The process that would normally drag a black hole down to the centre of a galaxy, called dynamical friction, is painfully slow, so wanderers can spend billions of years roaming the outskirts.

Two Cities, Two Sets of Rules

To study how these different black hole “life paths” shape, and are shaped by, their host galaxies, the authors turned to two cosmological simulations, ASTRID and TNG300, which handle black hole physics quite differently.

In TNG300, black holes are assumed to start fairly massive and are snapped straight to the centre of their host galaxy at every timestep. This makes mergers happen quickly and often, but it also means there’s no such thing as a wandering black hole in TNG300.

ASTRID, on the other hand, seeds smaller black holes and lets them move more realistically through their galaxy using a subgrid dynamical friction model. This is what allows wandering black holes, with their slow, aimless orbits, to exist and be studied in the first place.

Figure 1 reveals a lot at once. First, ASTRID (the simulation that allows wandering black holes and tidally stripped satellites) has whole new neighbourhoods on the map that simply don’t exist in TNG300. Those populations clearly aren’t following the same tidy, linear coevolution that central black holes enjoy with their galaxies. Second, the most massive black holes tend to be the most yellow, meaning mergers did the heavy lifting for their growth. This is especially pronounced in TNG300, where roughly 80–90% of the growth of the most massive black holes comes from mergers. Meanwhile, the wanderers and stripped satellites sit at the deep-purple end: these black holes have barely merged with anyone at all.

Figure 1: How black hole mass relates to host galaxy stellar mass, shown at two snapshots in cosmic history, 8 and 5 billion years ago, for both simulations (ASTRID: top row; TNG300: bottom row). Colour shows what fraction of each black hole’s growth since the last snapshot came from mergers, from purple (grown almost entirely by slowly swallowing gas) to yellow (grown mostly by swallowing other black holes). [Weller et al. 2026]

Four Kinds of Black Hole Life Stories

Pulling all of this together, the authors sketch out a kind of “neighborhood map” of black hole fates, sorted by where a black hole ends up on the mass-relation plot and how it got there (see Figure 2).

Figure 2: The distinct black hole populations revealed by the black hole mass–stellar mass relation, and the evolutionary path that lands each population in its corner of the map. [Weller et al. 2026]

• Normal centrals are the homebodies. They sit at the centre of primary or satellite galaxies and grow up steadily alongside their hometown, climbing the mass relation together through a healthy mix of accretion and the occasional merger. Their galaxies keep forming stars the whole time in a functional, unremarkable, thoroughly nice place to live.
• High-mass centrals are the ones who “made it.” These are central black holes in big primary galaxies, and their growth comes overwhelmingly from mergers with other black holes. Once they get big enough, they start throwing their weight around: their jets blast gas out of the galaxy, shutting down both star formation and their own further growth.
• Stripped satellites are the annexed suburbs. They start out on the normal mass relation, but a merger with a bigger galaxy tears away their gas and stars, shrinking their stellar mass while their black hole is left comparatively overweight for its new, smaller home. With their gas reserves gone, star formation grinds to a halt, and their black holes, starved of fuel, barely grow either.
• Wanderers are the ones who moved to the big city and never quite settled in. They start out on the normal relation inside a satellite galaxy, but when that galaxy merges into something much bigger, they’re left drifting through unfamiliar, low-density territory. With little gas around to feed on and almost no chance of merging with anyone else, their growth basically stalls.

This four-way map is a genuinely useful new way to read the black hole–galaxy relation: a black hole’s exact position on the plot isn’t just a number, it’s a fossil record of everywhere it’s ever “lived.”

There’s plenty more in the article we haven’t covered here, including how quenching plays out over time, how these results stack up against the local universe, and a closer look at how star formation rates and black hole accretion rates track each other across all four populations. If any of this piqued your interest, the full article is well worth a read.

Original astrobite edited by Ryan White and Chloe Klare.

About the author, Jayde Willingham:

I am a first-year PhD student at Swinburne University of Technology studying the early universe and how the first galaxies came to be. My work combines observations and theoretical modelling to explore how galaxies form, evolve, and shape the universe we see today. When I’m not at my desk or doing SciComm, I’m probably reading a good book with a hot beverage under a cozy blanket.

The post Not All Black Holes Who Wander Are Lost appeared first on AAS Nova.

Researchers have followed up on the discovery of a rare binary system containing a white dwarf and a brown dwarf. This unusual pairing offers valuable insights into the physics of atmospheres subjected to strong radiation.

Odd Couple

In 2025, researchers searching through observations from the Transiting Exoplanet Survey Satellite (TESS) spotted an eclipsing binary system in which a brown dwarf orbits the white dwarf J0404+1112 every 2.93 hours. Only about a dozen white dwarf–brown dwarf binaries have been confirmed so far, and each newfound system offers clues to how substellar or planetary companions survive a star’s transition from main-sequence star to swollen red giant to blazing white dwarf.

Because the two objects orbit one another so closely, this remarkable system also offers researchers an opportunity to study the dynamics and chemistry of an atmosphere blasted with high-energy radiation, with important implications for close-in brown dwarfs and giant planets.

Insights from New Observations

Eclipse photometry of J0404+1112 from TESS, SPECULOOS, the Gran Telescopio Canarias, and the United Kingdom Infra-Red Telescope. [de Wit et al. 2026]

Now, the team has obtained new photometry from the Gran Telescopio Canarias and the United Kingdom Infra-Red Telescope, plus spectroscopy from the Gran Telescopio Canarias, to get a better sense of the system. These observations allowed them to break the degeneracies in the white dwarf’s properties, showing it to be an 0.60-solar-mass white dwarf that has been cooling for more than 10 million years to a present-day temperature of 28,000K. The brown dwarf also appears to be more massive than initially thought, weighing in at roughly 40 Jupiter masses.

This diagram shows the relative sizes of the brown dwarf and the white dwarf. [AAS Nova/Kerry Hensley]

Like Night and Day

Because the system’s orbit is almost exactly edge on from our point of view, the white dwarf is completely eclipsed as the much larger brown dwarf passes in front of it. This allows the contributions from the two components to be separated, and for the emission from the brown dwarf’s nightside to be measured. The authors constrained the brown dwarf’s nightside temperature to roughly 1750K. Its dayside temperatures are likely to be significantly higher — potentially around 3750K at the point where the white dwarf is directly overhead — but more data are needed to constrain the dayside temperature of this world.

Day–night temperature difference (left) and irradiation flux (right) of the brown dwarf in this system compared to other white dwarf–brown dwarf systems and hot and ultra-hot Jupiters. Click to enlarge. [de Wit et al. 2026]

Citation

“J0404+1112: A 3 hr Eclipsing White Dwarf–Brown Dwarf Probing Multiple Atmospheric Regimes,” J. de Wit et al 2026 ApJL 1009 L40. doi:10.3847/2041-8213/ae9a97

The post Astronomers Get a Better Look at a Rare White Dwarf–Brown Dwarf Pair appeared first on AAS Nova.

Researchers have assessed the diffusion and scattering within an ultraviolet instrument on board Solar Orbiter, which takes detailed observations of our home star from as close as about 60 au.

The post A Point-Spread Function for the Extreme Ultraviolet High-Resolution Imager on Board Solar Orbiter appeared first on AAS Nova.

Pairing cold dark matter simulations with observations of stellar streams and globular clusters, researchers have extracted a declining power-law-like globular cluster initial mass function.

The post Inferring Globular Cluster Initial Mass Function from Stellar Streams appeared first on AAS Nova.

Emission arising from the merger of stellar-mass black holes in an active galactic nucleus disk should be identifiable through monitoring of order 1,000 active galactic nuclei of sufficient luminosity for a year.

The post Electromagnetic Flares from Compact-Object Mergers in Active Galactic Nucleus Disks: Signatures and Predictions appeared first on AAS Nova.

Roughly one-third of stars in the Milky Way are in binary or multiple systems, but only ~1–10% of stars in globular clusters have a companion. Did globular clusters start with fewer binaries than the solar neighborhood, or have they since been wiped out? 

Survival of the Tightest

Map of the semi-major axis–primary mass parameter space for binary systems. Solid lines show the boundary between hard (below the line) and soft (above the line) binaries for a variety of models. Models A–K span a variety of cluster masses and virial radii (a proxy for cluster density). [O’Connor et al. 2026]

It turns out that the fate of a binary system depends on whether it is dynamically “hard” or “soft.” Hard binaries are generally tightly bound, and they tend to get “harder” from stellar flybys, which are common in a crowded cluster environment. Soft binaries are the opposite — they have much shorter lifetimes since encounters with other stars tend to loosen them. The team found that, assuming GCs have the same initial distribution of binaries as the solar neighborhood, the dissolution of soft binaries is sufficient to explain the present-day scarcity of binaries in GCs. 

Burning Away the Binaries

What actually tears the soft binaries apart? The answer is a process called “black hole burning.” As some of the most massive objects in a globular cluster, black holes in binary systems can transfer energy when they interact with passing stars. This influx of energy can excite soft binaries to the point of dissolution, the study shows. 

Black hole burning can also prevent core collapse in GCs. Left to itself, a cluster’s core gradually loses energy to its outskirts, causing the core to grow hotter and denser with stars. This leads to more dynamical interactions between stars that can then get flung from the core or enter new tight binaries. Black hole burning pumps energy back into the core and prevents this from happening. 

Putting the Theory to the Test

The total number of black holes in a cluster (top) and the binary fraction (bottom) as a function of time for three different cluster models. In the densest cluster (blue), binary dissolution starts early on, mainly driven by stellar collisions. For the other two models, binary dissolution mainly occurs after the number of black holes reaches its peak and black hole burning commences. [Adapted from O’Connor et al. 2026]

In general, the final binary fractions of the simulated clusters agree with those predicted by the team’s analytical formalism. This further supports the theory that there is a universal initial binary distribution between galactic GCs and our solar neighborhood. Constraining this distribution is pivotal for refining dynamical models of GCs.

In short, GCs and the solar neighborhood likely started with the same amount of binary systems, and interstellar dynamics handled the rest. 

Citation

“A Common Origin for Binary Fractions in the Field and in Dense Clusters,” Christopher E. O’Connor et al 2026 ApJ 1009 L80. doi:10.3847/1538-4357/aea078

The post Catching the Culprit Behind Globular Clusters’ Disappearing Binaries appeared first on AAS Nova.

After identifying a new globular cluster, HSC 61, belonging to the Sagittarius dwarf galaxy, researchers have mapped the stellar stream, determined its metallicity, and analyzed the Sagittarius merger event.

The post The Properties of Globular Clusters and Elqui Associated with the Sagittarius Dwarf Galaxy appeared first on AAS Nova.

The Sun’s surface is peppered with spikes of plasma called spicules that appear to shift and twist over time. Recent simulations suggest a new explanation for the motion of solar spicules.

Solar spicules as seen by the Hinode mission. [Adapted from Dey et al. 2026]

Jets in Motion

Solar spicules are tiny jets of solar plasma that last just a few minutes. When viewed along the solar limb, spicules resemble blades of grass blowing in the wind. Observations show these structures moving in a variety of ways: twisting, shifting side to side, splitting, and joining together. Though spicules were first identified more than a century ago, where these motions come from is still up for debate.

In a recent research article, Sahel Dey (University of Newcastle; Indian Institute of Astrophysics; Indian Institute of Science) and collaborators performed 3D magnetohydrodynamics simulations to investigate the source of solar spicules’ motion. The team’s simulations encompassed a volume of 6,000 × 9,000 × 37,000 kilometers that stretched from beneath the visible surface of the Sun up to the lower region of the Sun’s outer atmosphere, or corona. In this region, they applied a uniform vertical magnetic field, mimicking the conditions within a coronal hole, where the Sun’s magnetic field streams outward into the solar system

A) A three-dimensional view of simulated solar spicules, showing curtain-like structures. B) Intensity of synthetic emission from the spicules in panel A, integrated along the line of sight. The cyan circle indicates the same region in both panels. [Adapted from Dey et al. 2026]

Simulating Spicules

The jet-like appearance arises when this arrangement is viewed from the side; the team created synthetic images of their simulated spicules that show individual jet-like features. These “jets” have properties similar to those of real spicules, lasting just 5–10 minutes, journeying upward at 20–70 kilometers per second, and reaching heights of 6,000–16,000 kilometers.

These simulations clearly demonstrate that what appear to be individual jets can arise from curtain-like plasma structures. Dey and collaborators showed that this network of spicules evolves over time, buoyed upward from below by a series of shocks, pulled down gradually by gravity, and buffeted by adjacent plasma.

Three-dimensional view of spicules (purple–yellow regions) and coronal swirling conduits (represented by spiraling black lines). [Adapted from Dey et al. 2026]

This work demonstrates that a curtain-like configuration provides a viable explanation for the observed variety of spicule motions. Going forward, it will be critical to test this possibility further, as correctly interpreting the underlying structures of solar spicules is key to understanding how mass and energy are transferred to the solar corona.

Citation

“Solar Spicule Rotation Driven by Plasma Curtain–Vortex Interactions,” Sahel Dey et al 2026 ApJ 1008 132. doi:10.3847/1538-4357/ae8999

The post Drawing Back the Curtain on Solar Spicules appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Phase-Dependent Magnetic Coherence in the Turbulent Interstellar Medium
Authors: Iryna S. Butsky et al.
First Author’s Institution: Stanford University
Status: Accepted to ApJ

The space between stars isn’t empty, because it’s threaded with magnetic fields that shape how gas moves and steer cosmic rays as they race across the galaxy. As a result, understanding how the magnetic field is structured within different components of the interstellar medium, specifically clouds of different temperatures, is a key part of understanding how the interstellar medium we see today takes shape.

Because magnetic fields are invisible, astronomers need tracers to reveal their structure. One such tracer is the emission from dust grains. Dust grains are not spherical, and a dust grain’s long axis tends to align at a right angle to the magnetic field, causing dust grains to emit light that vibrates in a particular direction. This is called polarized emission. If the magnetic field in a region is very ordered, the grains all align the same way, and a large fraction of their emitted light vibrates in the same direction, giving a high polarization fraction. This fraction is therefore used as a proxy for whether the field can maintain a consistent direction on large scales (an ordered/regular magnetic field).

Comparing the polarization fraction with other tracers of gas lets astronomers infer the field’s structure in the interstellar medium. Previous observations found that the polarization fraction correlates with the fraction of cold gas, but not with the total amount of gas along the line of sight. This suggests that the field is preferentially ordered within cold clouds rather than warm clouds. Curiously, this seemed to contradict other studies that found the field to be more ordered in the warm clouds. Such disagreements are where simulations become useful: because the true magnetic field is known in a simulation, astronomers can test which interpretation the observations actually support.

In this article, the authors use high-resolution numerical simulations to reproduce the relationship between polarization fraction and cold cloud fraction. They find that as long as the line of sight crosses fewer than about 20 clouds, the polarization fraction correlates with the cold cloud fraction, but not with the total neutral gas (Figure 1). This matches earlier observations, where the correlation shows up at high galactic latitudes, which point out of the galactic plane and therefore cross only a few cold structures. When too many clouds lie along the line of sight, each cloud carries an ordered field pointing in a different direction. Averaged together, these vibration directions cancel out, lowering the polarization fraction and washing the correlation away.

Figure 1: Correlation between dust polarization fraction, the total gas amount (neutral hydrogen column density, N_HI), and the fraction of cold medium along the line of sight (f_CNM) for projections of different path lengths. The polarization fraction correlates with f_CNM but not with N_HI. The correlation disappears once many clouds lie along the line of sight (see lower-right panel). [Butsky et al., in press]

Figure 2: Distribution of the angle difference between the average magnetic field and the line of sight for cold and warm clouds, shown for clouds matched by mass and by length. A smaller angle difference means a more ordered field. At similar mass, cold clouds show a more ordered field; at similar length, the reverse holds. [Adapted from Butsky et al., in press]

This apparent paradox comes from the different nature of cold and warm clouds. Cold clouds are denser and more compact, occupying much smaller physical scales than warm clouds. So to match the length of a warm cloud, you have to string together several cold structures, sampling more of the field’s variation and making the cold gas look disordered. Measured per unit length, then, warm clouds appear more ordered. Measured per unit mass, cold clouds appear more ordered. Crucially, when we observe dust emission, we are naturally weighting by mass, so real observations effectively trace the polarization fraction per unit mass, the regime in which the cold clouds are the more coherent phase.

In the end, this work shows that the ordering of interstellar magnetic fields depends on both the gas phase and how we choose to measure it. Cold clouds carry more coherent fields per unit mass, which is exactly the quantity dust observations trace, resolving an apparent contradiction between earlier studies. It is a reminder that even our best observations come with hidden assumptions, and that simulations, where the true field is known, are essential for interpreting what the sky is really telling us.

Original astrobite edited by Viviana Cáceres.

About the author, Sandy Chiu:

I’m a PhD candidate at the University of Michigan, Ann Arbor. I’m interested in numerical simulations of cosmic rays feedback in galaxies and their comparison with observation.

The post The Invisible Architecture Between the Stars appeared first on AAS Nova.

The Gelato mission would collect a sample from the surface of the comet 67P/Churyumov–Gerasimenko, gathering material that, unlike coma materials collected in previous missions, is relatively unprocessed.

The post Gelato: A Mission Concept for Comet Surface Sample Return appeared first on AAS Nova.

Follow-up observations show that a recently discovered pulsar has two stellar companions, making it one of just a handful of millisecond pulsars known to be in triple-star systems.

An Unusual New Pulsar

Earlier this year, researchers reported the discovery of a pulsar with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The newfound pulsar, PSR J0435+3233, is a millisecond pulsar, rotating once every 3.2 milliseconds. What’s unique about this pulsar is how quickly it’s spinning down: its spin rate is decreasing roughly 100 times faster than other millisecond pulsars in our galaxy, suggesting an unusually strong magnetic field and the possibility of an exotic formation pathway.

The FAST observations also showed that the pulsar is not alone: it appears to be on an 8-day orbit with a white dwarf. Now, follow-up observations have revealed the pulsar’s membership in an intriguing stellar system.

From Radio to Gamma Rays

Zonglin Yang (National Astronomical Observatories, Chinese Academy of Sciences) and coauthors followed up on the discovery of PSR J0435+3233 using multiwavelength data from FAST, multiple optical and infrared observatories, and the Fermi Gamma-Ray Space Telescope.

Visible-light image from PanSTARRS of the outer subgiant companion. [Adapted from Yang et al. 2026]

Insights into Stellar Evolution

While it’s common to find millisecond pulsars in binary systems — in fact, many millisecond pulsars are thought to spin up to their incredible speeds via accretion from a stellar companion — it’s rare to discover them in triple systems. Because this system is isolated out in the field rather than crowded together with other stars in a dense cluster, Yang and collaborators suspect that the three stars have been together since birth, as opposed to being assembled dynamically later on.

Projected orbits of the three stars in the system. Click to enlarge. [Yang et al. 2026]

Triple-star systems are common among massive stars, but how this configuration affects stellar evolution is still being explored. This discovery offers a valuable opportunity to study dynamics and stellar evolution in a rare triple system.

Citation

“The PSR J0435+3233 Triple System,” Z. L. Yang et al 2026 ApJL 1010 L9. doi:10.3847/2041-8213/aeaa29

The post A Pulsar in a Rare Triple System appeared first on AAS Nova.

The kinematics of small Milky Way satellites should differ depending on whether dark matter is warm or cold; current data constrain the mass of warm dark matter particles to >5.8 keV at 95% confidence.

The post Testing Warm Dark Matter with Kinematics of the Smallest Galaxies appeared first on AAS Nova.

Through modeling, researchers determined that a recently discovered supernova accompanied by an X-ray flash likely gave rise to a long-lived magnetar that may be surrounded by an accretion disk.

The post EP250827b/SN 2025wkm: An X-Ray Flash-Supernova Powered by a Central Engine and Circumstellar Interaction appeared first on AAS Nova.

In 3 million years or less, WASP-12b will tumble into its host star. It’s not surprising that the planet will meet its end this way, but it is surprising that it will happen so soon. New work tests a potential explanation for the planet’s rapid orbital decay.

Diagnosing a Doomed Planet

Roughly twice as wide as Jupiter and almost 50% more massive, exoplanet WASP-12b zips around its Sun-like stellar host every 1.09 days at a distance of just 0.023 au (3.4 million kilometers or 2.1 million miles). If placed in our solar system, WASP-12b would easily dethrone Mercury as the nearest planet to the Sun.

Observations show that WASP-12b’s already tiny orbit is shrinking, with each orbital period growing shorter at a rate of 29 milliseconds per year (Earth-year, that is). While we would expect the planet to slowly spiral inward due to tidal interactions with its star, it’s moving several orders of magnitude faster than predicted. The planet’s motion has so far defied all attempts to explain it, and now, a new research article by Caleb Lammers (Princeton University) and collaborators appears to topple yet another hypothesis for WASP-12b’s unexpectedly fast orbital decay.

A Tidy Tidal Explanation?

Previous work has proposed that WASP-12b’s rapidly shrinking orbit is due to obliquity tides, which could come into play if the planet had a nonzero obliquity, or axial tilt. Tidal dissipation generally works to keep close-in giant planets like WASP-12b from having a significant axial tilt. However, if you throw a second planet into the system, the companion can exert a torque that could force WASP-12b to remain tilted. This outside forcing, the hypothesis suggests, changes the orbital, spin, and tilt evolution of WASP-12b and ultimately pushes it toward its star far faster than expected without the tilt or the companion.

Constraints on the mass and orbital distance of the companion planet in the obliquity-tide scenario. The color shows the radial velocity signal associated with each combination of parameters. The green line shows the maximum radial velocity allowed by observations. Click to enlarge. [Lammers et al. 2026]

The Mystery Persists

This companion mass and orbital distance are both larger than predicted by previous work, which had suggested that a 10–20-Earth-mass planet at 0.04 au would be sufficient to drive WASP-12b’s inward journey. Lammers and coauthors analyzed WASP-12’s radial velocity data for evidence of such a planet tugging on the star, but found none; only under extremely particular conditions could such a planet exist and not be detected in current data.

Radial velocity constraints on the properties of a hypothetical second planet in the WASP-12 system, obtained via injection-recovery tests. [Lammers et al. 2026]

Citation

“The Mysterious Inspiral of WASP-12 b: Why Obliquity Tides Cannot Drive Orbital Decay,” Caleb Lammers et al 2026 ApJL 1009 L43. doi:10.3847/2041-8213/aea405

The post Tilting WASP-12b Doesn’t Solve the Mystery of Its Inspiral appeared first on AAS Nova.

The molecular cloud complex G12.79+0.43 contains 82 young stellar object candidates; while this complex is spatially associated with a larger superbubble, it’s not yet clear if there is a causal association.

The post Star Formation at the Periphery of a Molecular Superbubble: The Case of G12.79+0.43 appeared first on AAS Nova.

Eruptions taking place in different locations on the Sun (e.g., on the solar limb versus on the disk) appear to have different spectral characteristics, paving a way for source regions of stellar flares to be studied.

The post Can We Distinguish the Source Region Location of Filament/Prominence Eruptions from the Sun-as-a-Star Hα Spectrum? appeared first on AAS Nova.

What at first might appear to be abstract pixel art or a fuzzy photograph of skyglow from a distant city is actually a representation of radio emission from the pulsar at the center of the Crab Nebula. When a pulsar’s radio emission passes through a region of ionized gas — like the complex filaments of the Crab Nebula — the plasma deflects the radio signal from its intended course. This detour can create “echoes”: copies of the pulsar signal that arrive later than the original pulse. Thierry Serafin Nadeau (University of Toronto) and collaborators studied these echoes from the Crab pulsar by compiling an archive of giant pulses detected over 2.5 years by the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Giant pulses, which are brighter and narrower than typical pulses, offer a powerful way to probe plasma echoes. The image above shows sweeping parabola-shaped echoes during two particularly active periods. The color shows the frequencies at which power was received: mainly at low (blue), high (red), or all (yellow-white) frequencies. This dataset revealed for the first time a feature predicted to exist but never seen: echoes from plasma structures that never pass directly in front of the pulsar from our point of view. To learn more about the echoes of the Crab pulsar, be sure to check out the research article linked below.

Citation

“Echoes in Different Tempo: Long-Term Monitoring of Crab Echoes with CHIME,” Thierry Serafin Nadeau et al 2026 ApJ 1006 82. doi:10.3847/1538-4357/ae7336

The post Featured Image: Echoes of Giant Pulses appeared first on AAS Nova.

The upcoming Wide Fast Deep and Deep Drilling Field surveys have limited potential to confirm exoplanets, with just a handful of hot planets around M-dwarf stars likely to be confirmed in the Deep Drilling Field.

The post Predictions of Transiting Exoplanet Confirmations from Rubin LSST Surveys appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: The SPHEREx Satellite Mission
Authors: James J. Bock et al.
First Author’s Institution: California Institute of Technology; Jet Propulsion Laboratory
Status: Published in ApJ

You know JWST. You’ve likely heard about the recently launched Nancy Grace Roman Space Telescope. But did you know that NASA launched a third space telescope focused on infrared astronomy just last year? That telescope, called SPHEREx (short for Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer, but we’ll forgive the tortured acronym), is currently carrying out its ambitious mission to record an infrared spectrum for every point in the sky. Let’s break down SPHEREx’s three main science goals and then discuss how SPHEREx will accomplish its mission.

Goal #1: Stress-Testing Cosmic Inflation

According to our best current models of cosmology, the very early universe experienced a rapid burst of accelerating expansion called cosmic inflation. During inflation, small regions of the universe that by chance had slightly higher energy density than their neighbors (due to quantum fluctuations) expanded to huge scales. Because these regions were very gravitationally attractive, once inflation ended, they became the seeds where matter accumulated and eventually formed galaxies.

This means that the distribution of galaxies that we see today is a reflection of the properties of inflation (i.e., what the quantum fluctuations were like and how inflation supersized them). SPHEREx will assemble the largest atlas of galaxies ever, recording the three-dimensional positions of hundreds of millions of galaxies across the entire sky. To do this, SPHEREx must figure out how far away these galaxies are from Earth, using their redshifts. SPHEREx’s low-resolution infrared spectroscopy allows for moderately precise measurements of these redshifts. By performing statistical analyses of how galaxies are separated from each other, SPHEREx will test different theories of inflation, like whether inflation was driven by multiple fields.

Goal #2: Frozen Assets

Astronomers are racing to find evidence for life (or at least habitability) in the atmospheres of exoplanets through transmission spectroscopy. However, we don’t know for sure how molecules that could be used in biological processes (called biogenic molecules, these include water, carbon dioxide, carbon monoxide, and methanol) even end up on planets.

We think that a large fraction of these molecules are frozen onto dust grains throughout the interstellar medium. When a new star forms in the interstellar medium, this ice and dust would become part of the star’s protoplanetary disk. The ice species can help create planetesimals (which may grow into planets) or can later deliver biogenic molecules to planetary surfaces. Earth’s oceans likely came (at least in part) from collisions with icy asteroids. As Figure 1 shows, SPHEREx will measure the abundance of ice species in different environments that track the history of solar system formation, from dense clouds in the interstellar medium that may soon form stars to regions around newborn stars and evolving protoplanetary disks. In this way, SPHEREx will track how biogenic molecules from the interstellar medium can end up on planets.

Figure 1: Examples of the sources SPHEREx will look at to search for biogenic ice species. In the top left, what the spectra of these sources will look like if those species are present: each type of ice leaves a distinct fingerprint in an infrared spectrum. [Bock et al. 2026]

Goal #3: Your Noise Is SPHEREx’s Signal

SPHEREx will measure an infrared spectrum for every point in the sky — even those that don’t contain galaxies or stars that we can resolve. These points are instead dominated by diffuse extragalactic background light. This light comes from many different sources, including stars, dust, and quasars, from the early universe to the present day, all added together incoherently. For most telescopes, the extragalactic background light is just a frustrating source of noise. For SPHEREx, it’s a treasure trove. We can compare the properties of the extragalactic background light that SPHEREx measures (its spectrum and how it fluctuates across the sky) to theoretical predictions and see if we seem to be missing anything. SPHEREx’s very broad infrared spectra — capturing redshifted light from the very early universe — and total sky coverage are crucial for this purpose. For instance, the SPHEREx team will try to isolate emission from the first stars and galaxies, which ionized most of the gas in the universe in the epoch of reionization. By understanding this and other contributions to the extragalactic background light, we can test hypotheses about how galaxies form and evolve.

Making It Happen

Beyond inflation, ices, and extragalactic background light, SPHEREx’s all-sky infrared spectra will be invaluable for countless other science cases, like studying asteroids, characterizing the atmospheres of stars that host exoplanets, and even understanding the upper atmosphere of Earth, through which SPHEREx orbits.

But how can SPHEREx even make a spectrum for every point in the sky? An image of some part of the sky is fundamentally two-dimensional, and measuring how the brightness of every point changes with wavelength adds a third dimension. Astronomers have come up with many ways to solve this problem. Integral field spectroscopy approaches typically involve splitting an image into small regions or strips, then using a dispersive element like a prism or grating to make a spectrum of each region, and finally putting these spectra side by side on a camera. Figure 2 shows an example of this strategy, as well as what the final three-dimensional “datacube” looks like after processing.

Figure 2: A demonstration of the principle of integral field spectroscopy. [ESO; CC BY 4.0]

This is the SPHEREx survey strategy, with a few complications. First, before any filter, SPHEREx splits incoming light into two beams, with short-wave infrared light (SWIR, with 0.75 μm < λ < 2.42 μm) going in one direction and mid-wave infrared light (MWIR, 2.42 μm < λ < 5.00 μm) going in another. SPHEREx makes images with these two beams on different sets of detectors, so it can measure the brightness of an object at one SWIR wavelength and one MWIR wavelength simultaneously. The SPHEREx field of view covers 10.5° by 3.5°, with the SWIR and MWIR images each spread across three detectors. Every detector has a different linearly variable filter. To get a complete infrared spectrum of a given point in the sky, SPHEREx moves that point to 17 different positions on each detector. This requires 51 different telescope (17 × 3 detectors) pointings in all and yields 102 spectral values (51 × 2 for the SWIR and MWIR beams). Figure 3 shows the 17 bands on each of the six SPHEREx detectors, each corresponding to a different wavelength value.

Figure 3: The wavelength of light that each part of each SPHEREx detector is sensitive to. A point in the sky is imaged on one short-wave infrared detector (top row) and one mid-wave infrared detector (bottom row) simultaneously. SPHEREx measures each point in the sky at 102 different wavelengths by placing the point at 17 different positions on each of the detectors. [Adapted from Bock et al. 2026]

Original astrobite edited by Veronika Dornan.

About the author, Chris Layden:

Chris is a PhD candidate in astrophysics at the Massachusetts Institute of Technology. His primary research interest is developing instrumentation that enables high-speed astronomical observations. With such instruments, he studies the most rapidly varying phenomena in the sky, including millisecond pulsars, accreting black holes, and solar system objects whizzing past background stars. Outside of astronomy, Chris enjoys reading classic novels, playing ultimate frisbee, and hanging out with his wife and dog.

The post SPHEREx: The Niftiest Space Telescope You May Not Have Heard Of appeared first on AAS Nova.

A tentative gravitational wave signal sent astronomers searching for a possible electromagnetic counterpart. New radio observations weigh in on whether the candidate counterpart is a standard supernova or a sign of something rarer.

A Potential Neutron Star Merger

These images from the Hubble Space Telescope show the fading light of the kilonova associated with the gravitational wave event GW170817. [NASA and ESA Acknowledgment: A. Levan (U. Warwick), N. Tanvir (U. Leicester), and A. Fruchter and O. Fox (STScI)]

S250818k offered a rare opportunity to associate the light from a kilonova with a gravitational wave detection, a feat achieved only once so far, in 2017. The intrigue surrounding S250818k was heightened even further by the possibility that the collision involved at least one sub-solar-mass neutron star. Such a lightweight neutron star would fall below the lower mass limit set by stellar evolution models, requiring a different formation pathway.

S250818k’s kilonova potential rose and fell once researchers spotted an electromagnetic transient in its source region. Early optical observations revealed a kilonova-like color and rapid fading, while later observations showed brightening similar to a supernova interacting with circumstellar gas. This led the event to be classified as supernova SN 2025ulz — and therefore unlikely to be the source of the gravitational wave signal.

Illustration of a kilonova that occurs in the wake of a supernova. First, a massive star collapses. Then, neutron stars form in the aftermath. Finally, the neutron stars collide, producing a kilonova whose signal might be hidden by the supernova. [Caltech/K. Miller and R. Hurt (IPAC)]

A Kilonova in a Supernova?

Unlikely, but not impossible. Tanner O’Dwyer (Johns Hopkins University) and collaborators investigated the supernova for signs that it wasn’t a typical collapsing star. The team was motivated by theories suggesting that the collapse of a rapidly rotating massive star could produce both a kilonova and a supernova — potentially uniting gravitational wave signal S250818k and supernova SN 2025ulz.

In theory, the demise of a fast-spinning massive progenitor could produce one or more sub-solar-mass neutron stars. This could happen if 1) the collapsing stellar core splits into two neutron stars, or 2) in a twist on the star-formation process, neutron stars coalesce out of neutron-rich material in the disk surrounding the dying star. In either scenario, the neutron stars could merge shortly after the star’s collapse, generating kilonova emission that might be obscured by the expanding supernova.

Looking Deeply in the Radio

Very Large Array detection of a radio counterpart to SN 20215ulz. The circle shows the optical position of the supernova, and the “x” shows the optical position of the host galaxy. [Adapted from O’Dwyer et al. 2026]

The team found that standard supernova ejecta and relativistic jet models can both plausibly fit the data. In the supernova scenario, the estimated expansion speed and progenitor mass-loss rate place the event well within the bounds of known stripped-envelope supernovae. Though the data were also compatible with an off-axis relativistic jet, the authors were unable to resolve degeneracies in the event’s properties, including the jet energy and the interstellar medium density.

Ultimately, the authors suggested that a supernova fits the data more naturally. While this radio investigation didn’t unambiguously link S250818k and SN 2025ulz via an exotic kilonova-plus-supernova mechanism, it’s clear that radio observations have an important role to play in examining future gravitational wave signals.

Citation

“Identification of a Radio Counterpart to SN 2025ulz in the S250818k Localization Area,” Tanner O’Dwyer et al 2026 ApJL 1009 L44. doi:10.3847/2041-8213/aea4a5

The post Supernova, Kilonova, or Both? Another Look at SN 2025ulz appeared first on AAS Nova.

Using data taken with a novel slit-stepping observing mode, researchers have found an anticorrelation between radial metallicity gradients and radial mixing time for galaxies at z ~ 1.

The post MSA-3D: Connecting the Chemical and Kinematic Structures of Galaxies at z ∼ 1 appeared first on AAS Nova.

Each of the studied outbursts released roughly one hundred thousand to one million kilograms of material — similar to outbursts from other comets — and caused brightening episodes of –0.2 to –1.1 magnitudes.

The post A Look at Eight Outbursts of Comet 7P/Pons–Winnecke appeared first on AAS Nova.

Using high-cadence ultraviolet observations of solar flares over the course of 12 years, researchers have carried out a statistical survey that revealed rapid pulsation of small-scale flare structures.

The post Unprecedented Fast Winking of Solar Flares Triggered by Bursty Magnetic Reconnection appeared first on AAS Nova.

Isaac Newton suspected that the gravitational dance between the Sun and Jupiter would eventually destabilize the solar system, but modern computational research has shown that its long-term stability is, statistically, pretty secure. However, new simulations with more realistic solar mass-loss conditions make a strong case for the disassembly of the outer solar system — and on timescales much shorter than previously thought.

Kick It Up a Notch

Final outer planet orbital configurations for two simulations — one stable and one unstable. t=0 at the onset of white dwarf formation. Click to enlarge. [Adapted from Batygin et al. 2026]

However, all of these studies modeled solar mass loss as a smooth function, so the dismantling of the solar system was left up to external forcings. In reality, stars on the red giant branch undergo mass ejections that are random in time and direction, corresponding to velocity “kicks” that can alter the dynamics of the planets. 

A team led by Konstantin Batygin at the California Institute of Technology conducted numerical experiments to analyze the orbital dynamics of the outer solar system under different solar mass-loss conditions. First, they tested the classic case of smooth mass loss and validated previous findings that, despite planetary orbits doubling in size, the dynamics are pretty tame. This holds true even when mass is ejected anisotropically: if the timing is smooth, the asymmetries cancel out.

Outer Solar System, Your Days Are Numbered

Next, they simulated stochastic kicks and found that the behavior of the outer planets was largely tied to the ejection mass of each kick. For very small ejection masses (≤ 10^-7 M_☉), dynamics mimic the smooth mass-loss case. For intermediate values (10^-7 to 10^-6 M_☉), there’s a roughly 20% chance Jupiter–Saturn and Uranus–Neptune enter mean-motion resonances: an orbital configuration where planets’ periods are a ratio of small integers. These resonant configurations don’t protect the giant planets, however: resonant simulations disassemble slightly more often than nonresonant simulations. For larger ejection masses (≥ 10^-5 M_☉), the outer solar system disassembles on the timescale of billions of years. 

Instability onset time — or how long after white dwarf formation the outer solar system disassembles — as a function of ejection mass. The larger the ejection mass, the greater the chance of instability. Click to enlarge. [Batygin et al. 2026]

This new discovery reduces the life expectancy of the solar system from one billion billion years to a meager one billion years after white dwarf formation. 

Citation

“Terminal Instability of the Solar System Triggered by Stochastic Solar Mass Loss,” Konstantin Batygin et al 2026 ApJL 1009 L22. doi:10.3847/2041-8213/aea290

The post The Solar System Has a New Life Expectancy, and It’s a Billion Times Shorter appeared first on AAS Nova.

Dwarf elliptical galaxies in the Virgo Cluster appear to come in “flat” and “round” varieties; the dynamics of these populations suggest that flat dwarf ellipticals have experienced less tidal processing.

The post Tidal Grinding of Dwarf Galaxies in Cluster Environments appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Discovery of the Distant, Ultra-Faint Milky Way Satellite Aquarius IV with the Vera C. Rubin Observatory Early Data Preview 2
Authors: William Cerny et al.
First Author’s Institution: Yale University
Status: Published in RNAAS

Warming Up the World’s Largest Camera

Today’s bite covers one of the NSF–DOE Vera C. Rubin Observatory‘s first major discoveries, which was found in testing data before the observatory began its decade of observations. Perched atop a mountain in Chile, the brand-new Rubin Observatory is just beginning a 10-year survey called the Legacy Survey of Space and Time (LSST). LSST will be the deepest and widest sky survey ever conducted, taking images of the entire southern night sky every three nights. This ultra-wide, ultra-high-definition time-lapse of the universe will help answer fundamental questions about dark matter and dark energy, study objects in our solar system, find distant supernova explosions, and more.

LSST is a photometric survey, meaning its main data product is images in several filters. These images are taken with the largest digital camera ever constructed, about the size of a Mini Cooper. The LSST camera has a resolution of 3.2 gigapixels. To put that number into perspective, you would need about 13 copies of the Las Vegas Sphere to display just a single LSST image… and hundreds of these images will be taken every night!

The authors of today’s article use the first dataset from the LSST camera, called Early Data Preview 2 (EDP2). EDP2 was taken from April 2025 to January 2026, covered about 3,000 square degrees (about 7% of the entire night sky), and primarily served as a test before beginning the 10-year LSST (which began in June 2026).

Small Galaxies, Big Questions

Since LSST will survey a large area at unprecedented depths, one field of interest is to study extremely dim and small galaxies called ultra-faint dwarf galaxies (UFDs). These galaxies are so faint that we can only find them close to home, orbiting the Milky Way and other nearby galaxies as satellites. UFDs don’t have much luminous matter, meaning they are likely dominated by their dark matter halos. This makes them useful test beds for our theories of dark matter and galaxy formation, if we can spot them.

Many UFDs don’t look like normal galaxies that resemble blobs of diffuse light with stars; instead, they’re more like a handful of individual stars in an image that also contains foreground stars and background galaxies. So how do you identify them? The trick is that stars born together at the same time from the same gas follow a predictable track in color and brightness called an isochrone. The authors slide a model isochrone for an ancient, metal-poor population through the data at a range of assumed distances and ask: at any spot in EDP2, are there more stars sitting on that track than random chance would predict? Cerny and coauthors found a new spot, which they call Aquarius IV, a new UFD candidate (Figure 1).

Figure 1: Left: A Rubin image centered on Aquarius IV, combining images in the g, r, and z filters. The dashed circle marks the half-light radius, the region enclosing half the galaxy’s light. Aquarius IV is only a scattering of individual faint stars. The yellow star marks a likely blue horizontal-branch member. Right: A plot of brightness against color for the stars inside twice the half-light radius (first panel) and inside a ring of sky just outside the galaxy (second panel). Stars born at the same time from the same gas fall along the isochrone (blue line; any stars in the grey regions are deemed to follow the isochrone). All the stars follow the isochrone in the first panel but not the second, indicating that the stars are associated. [Adapted from Cerny et al. 2026]

The authors also infer several properties of Aquarius IV, including its centroid coordinates, half-light radius, ellipticity, distance, and absolute magnitude. They find that its radius is larger than almost all Milky Way globular clusters (tight gravitationally bound systems of old stars that don’t reside in their own dark matter halos), suggesting that Aquarius IV is a true dwarf galaxy.

Currently, there are about 40 known UFDs around the Milky Way, and LSST is expected to roughly double this number (see this Astrobite), allowing us to study these tiny galaxies at a population level. This article proves that LSST has the potential to revolutionize many areas of astrophysics! If you are a researcher in the US or Chile and want to play with the EDP2 data yourself, you can access it via the Rubin Science Platform. For researchers from other countries, see more info here.

Original astrobite edited by Katya Gozman.

About the author, Ben Sherwin:

I am a physics PhD student and NSF Graduate Research Fellow at Stanford University. I am interested in theoretical and observational cosmology, specifically in cross-correlations between the cosmic microwave background and tracers of large-scale structure. Outside of work, I enjoy seeing the latest movies in theaters and exploring the San Francisco Bay Area.

The post An Early Discovery by Rubin Observatory appeared first on AAS Nova.

Analysis of Cassini spectra of Titan suggests that JWST is unlikely to identify atmospheric components aside from methane on a Titan-like exoplanet; optical and near-ultraviolet observations will be key.

The post Piercing Through the Haze: Characterizing Titan-Like Terrestrial Exoplanets with JWST appeared first on AAS Nova.

Astronomers seem to find something new every time they point a telescope at WISPIT 2, a 5-million-year-old solar-mass star located 430 light-years away. New high-resolution radio observations provide the best view yet of how the young planets of this system interact with the disk that feeds them.

Detecting Distant Planets

In 2025, astronomers carrying out the WIde Separation Planets In Time (WISPIT) survey — a targeted search for widely separated giant planets around young Sun-like stars — revealed a dusty disk surrounding the star WISPIT 2. Orbiting within this disk is a 4.9-Jupiter-mass planet, WISPIT 2b, at 57 au from the star. This makes WISPIT 2 just the second star to host a confirmed, directly imaged planet within its protoplanetary disk. Even more remarkable, WISPIT 2b was detected in Hα, showing that the planet is still growing by accreting gas from the disk.

Later observations confirmed the presence of a second planet, WISPIT 2c, which has an estimated mass of 8–12 Jupiter masses and orbits the star at 15 au. On top of these planetary discoveries, researchers have also found that WISPIT 2 is two stars rather than one!

Best View Yet of the WISPIT 2 System

New observations of WISPIT 2 from ALMA (left and center panels) and previous observations from the Very Large Telescope (right panel). The star is shown by the small dot at the very center, and the planets are indicated by the two white circles. Click to enlarge. [Adapted from Benisty et al. 2026]

The distribution of gas within the disk, traced by emission from carbon monoxide, roughly follows the pattern seen in previous observations of small dust grains: the orbits of WISPIT 2b and 2c are depleted of gas and dust, demonstrating how the young planets have carved their own berths within the disk, creating a gap at WISPIT 2b’s orbit and a cavity around the star.

The left panel shows the dust continuum emission zoomed in on the star (plus sign) and planets (circles). The dotted line shows the location of a faint ring, which is modeled in the center panel. The right panel shows the residuals. Click to enlarge. [Benisty et al. 2026]

Spiral Wakes Making a Splash

Velocity field showing the gas swirling around WISPIT 2b, which is indicated by the green circle farther from the star. [Benisty et al. 2026]

Spiral wakes have been spotted in other protoplanetary disks, but this is the first time researchers have been able to definitively associate this feature with a planet rather than other causes, such as gravitational instabilities. Looking ahead, future high-resolution spectroscopic observations of WISPIT 2b and its surroundings will offer researchers an unprecedented opportunity to compare the properties of the planet and its spiral wake against the predictions of simulations — advancing toward a powerful new way to study exoplanets embedded in protoplanetary disks.

Citation

“Mapping the WISPIT 2 Planet-Hosting Cavity at Sub-Hill-Radius Scales,” Myriam Benisty et al 2026 ApJL 1009 L32. doi:10.3847/2041-8213/aea214

The post Researchers See Gas Swirling Around a Growing Baby Planet appeared first on AAS Nova.

By observing subtle variations in the timing of stellar pulsation modes, researchers may have made the first detection of a planet in the habitable zone of a massive A-type star.

Listening for Planets in Stellar Heartbeats

To date, some 6,000 exoplanets have been detected across a vast array of surveys and instruments. The majority of these have been detected around main-sequence F, G, and K stars — but not because these are the only places exoplanets can exist. Rather, this is a result of selection bias: these stars tend to be both bright and luminously stable enough for astronomers to deploy the radial velocity or transit methods.

Periodic modulations in the time of observed stellar pulsations can indicate the presence of an orbiting companion. In this case, timing variations are displayed for the two most prominent pulsation modes f1 and f2 for the variable star HD 156295. The sinusoidal pattern indicates they may be caused by an orbiting companion with a mass of about 6.3 Jupiter masses at a distance of 3.9 au, in this star’s habitable zone. [Adapted from Wilson et al. 2026]

Luckily, one transit astronomer’s trash data can be a pulsation timer’s treasure. For some A-type stars called δ Scuti stars, the pulsation is regular enough to be used like a cosmic clock. Subtle variations in a star’s position due to the tug of an orbiting companion can then disrupt the timing of its otherwise steady pulsation, allowing one to once again find planets via its light curve — including massive ones on intermediate-period orbits that are the most difficult to detect around massive stars using traditional methods.

A Massive Planet in the Habitable Zone of a Hot Star?

In a new study led by Logan Wilson (Center for Astrophysics | Harvard & Smithsonian), researchers analyzed 16,440 highly pulsating δ Scuti stars observed at a high cadence by the Transiting Exoplanet Survey Satellite (TESS) in order to look for the distinctive, periodic timing modulations associated with an orbiting companion. This sample was then whittled down to nine candidate systems they believe may contain substellar companions — likely either brown dwarfs or massive planets.

The properties of the nine candidate objects identified in this study and their host stars are shown here, along with the properties of other exoplanet systems. Through stellar pulsation timing, the researchers were able to identify substellar candidates around hot A-type stars in intermediate-period orbits, a region of parameter space that has been difficult to probe with other methods. [Wilson et al. 2026]

The other eight candidates are more consistent with brown dwarfs. Six of these candidates show somewhat uncommon masses and orbital separations that place them in a region of parameter space known as the “brown dwarf desert.” Some observations suggest this desert is less severe around hotter stars — a conclusion that this study supports.

All of these findings are still quite tentative, however; the researchers estimate that the probability for the planetary signal being real is just over 50%, and the parameters given for each candidate are still subject to large uncertainties. With new data arriving all the time, it may not take long before we have a clearer picture of these unique substellar companions.

Citation

“A Search for Substellar Companions around A-type Stars: Pulsation Timing Detection of Eight Brown Dwarf Candidates and a Possible Habitable-zone Planet,” Logan G. Wilson et al 2026 ApJ 1009 78. doi:10.3847/1538-4357/ae93a0

The post Stellar Pulsations Suggest Habitable-Zone Planet Around a Massive Star appeared first on AAS Nova.

A concentration of galaxies four times denser than expected provides an opportunity to understand how environment impacts galaxy evolution and the onset of reionization.

The post JADES: A Prominent Galaxy Overdensity Candidate Within the First 500 Myr appeared first on AAS Nova.

Using light curves from the Transiting Exoplanet Survey Satellite (TESS), researchers have performed an asteroseismic analysis of 221 main-sequence and subgiant solar-like oscillators.

The post Solar-Like Oscillations of Main-Sequence and Subgiant Stars in the TESS Field appeared first on AAS Nova.

Sunrise III, a stratospheric balloon-borne solar observatory, took a 6.5-day flight from northern Sweden to northwestern Canada in 2024, gathering 200 TB of data with its 1-meter telescope and three instruments.

The post Sunrise III: Instrument, Mission, Data, and First Results appeared first on AAS Nova.

Humans have recorded solar eclipses for thousands of years. Recently, researchers translated and analyzed solar eclipse observations from 18th-century Sweden to determine the Sun’s radius at that time and study the first confirmed record of solar prominences.

Looking Back Nearly 300 Years

The path of the 13 May 1733 total solar eclipse. Click to enlarge. [Eclipse Predictions by Fred Espenak (NASA’s GSFC)]

Wassenius penned a short account of his observations in Latin for Philosophical Transactions of the Royal Society (the longest-running scientific journal in the world!). His drawings of the event, which include the first robust record of solar prominences, were never officially published, but were housed in the Royal Academy Archives of Sweden. Now, researchers have translated Wassenius’s full report from Swedish to English and analyzed his sketches, helping to fill an important gap in the historical record of solar activity.

Drawing from Observations

Hisashi Hayakawa (Nagoya University; Rutherford Appleton Laboratory) and collaborators translated Wassenius’s notes, which describe how he viewed the eclipsed Sun through a 21-foot-long telescope during just over two minutes of totality. From Wassenius’s measurements, Hayakawa and coauthors calculated the solar radius to be 696,250 ± 170 km; this is larger than the modern accepted radius, but it’s in line with what has been calculated from solar eclipse measurements two decades earlier, in 1715.

Wassenius’s sketch of the solar eclipse, showing three prominences as filled circles emerging from behind the disk of the Moon. [Adapted from Hayakawa et al. 2026]

Prominent Features

High-latitude prominences like the one (or more) seen by Wassenius are most common during what’s known as the “polar rush,” which occurs as solar activity rises toward a maximum. If these prominences are related to the polar rush, that would mean that in 1733, the Sun was not in an activity minimum as previously thought. However, it’s also possible for prominences to pop up at high latitudes during other times in the solar cycle; the authors estimated the likelihood of this happening at 20%.

Heliographic latitude of solar prominences estimated from Wassenius’s drawings (light blue circles), compared to the positions (filled symbols) and number (gray line) of sunspots. Note that sunspot data around this time were scarce, and some researchers have suggested that revisions to the sunspot number are needed. Click to enlarge. [Hayakawa et al. 2026]

Citation

“Analyses on Wassenius’s Report for Total Solar Eclipse in 1733: Quantifications of the Solar Radius and the Earliest Reported Prominences,” Hisashi Hayakawa et al 2026 ApJ 1007 189. doi:10.3847/1538-4357/ae6451

The post A New Look at a Centuries-Old Solar Eclipse appeared first on AAS Nova.

A recently identified opaque feature around the dwarf planet Quaoar appears to be inconsistent with an orbiting sharp-edged arc explained by triangular-point confinement; it’s likely a satellite instead.

The post Dynamical Implications of the Recently Detected Feature Around Quaoar and Constraints on the Presence of Additional Satellites appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Probing the IMF in the Early Universe — Direct Measurements in the Boötes I UFD with JWST/NIRCam
Authors: Keyi Ding et al.
First Author’s Institution: University of Maryland
Status: Published in ApJ

The Stellar Initial Mass Function

Figure 1: Several different formulations for the IMF. Astronomers have found that the Milky Way IMF seems to follow either a broken power law (Kroupa), or a log-normal (Chabrier) distribution. [JohannesBuchner; CC BY-SA 4.0]

For a relatively simple concept, the IMF is shaped by incredibly complicated underlying physical mechanisms. Things like turbulence, magnetic fields, and chemical enrichment all play a role in shaping the observed IMF. Additionally, the IMF is a pretty fundamental quantity. An enormous amount of astronomy research relies on assumptions made about the IMF. For example, since most stars are low in mass, and low-mass stars are dimmer, astronomers use the IMF to convert the amount of light in a galaxy to the number of stars; if there are more or fewer low-mass stars than we expect, our measurements will be wrong.

A big question surrounding the IMF is whether or not it’s universal. In the Milky Way, astronomers have been able to measure the IMF accurately, and they have found that it seems to be the same regardless of which bunch of stars we use to measure it.¹ However, we know that galaxies in the early universe were very different compared to today. Things get tricky when you acknowledge that most measurements made of early-universe galaxies rely on modeling tools that are entirely reliant on assuming an IMF. This gnarly little detail makes measuring the IMF in the early universe especially valuable to astronomers.

What Makes Ultra-Faint Dwarfs So Special?

Today’s authors attempt to measure the early-universe IMF using a local relic, an ultra-faint dwarf galaxy (UFD). You might describe UFDs as “incredibly funky little galaxies.” They’re much less massive than the Milky Way, with about 10,000 times less stellar mass. What stars they do have tend to be very old and metal poor. The nature of UFDs has led many astronomers to think of them as fossils: relatively untouched galaxies formed in the early universe. Since we think UFDs are fossils of earlier galaxies, measuring the IMF in a UFD tells us whether the IMF was the same in the early universe as it is today. The authors focus on Boötes I, a relatively luminous UFD orbiting the Milky Way. Figure 2 shows Boötes I as seen by the Sloan Digital Sky Survey.

Figure 2: Boötes I as seen by the Sloan Digital Sky Survey. Because they’re so diffuse, UFDs look less like galaxies and more like groups of stars. [Vasily Belokurov – SDSS-II Collaboration]

The IMF in Boötes I

Measuring the IMF can get tricky — it’s typically pretty difficult to measure the mass of each individual star in a galaxy. Thankfully, Boötes I is close enough that we can do exactly that! Using JWST’s NIRCam instrument, today’s authors obtain imaging of Boötes I that is sensitive enough to extract roughly 10,000 stars belonging to the galaxy.

To measure the IMF from the observed population of stars, the authors use a modified version of Starwave, a Bayesian inference tool. In short, the tool takes in some assumptions about the population of stars in the galaxy, then generates many potential color–magnitude diagrams for various parameter selections. You can then assess how well each simulated color–magnitude diagram fits the observed data, thus determining likely parameters for the stellar population. The authors apply their tool for three different IMF models, testing how close the IMF in Boötes I is to that of the Milky Way. This allows them to determine how well the IMF compares to that of the Milky Way, which is typically thought of as a broken power law or log-normal distribution. If the IMF in Boötes I aligns with the Milky Way’s IMF, we’ll have a solid piece of evidence for a truly invariant IMF across cosmic time, allowing astronomers to rest easy knowing our modeling efforts haven’t been bunk this whole time.

So… What Did We Learn?

The authors find that a single power law can be ruled out to a good degree of confidence. This is good, as Milky Way studies show undeniable evidence of a turnover in the distribution. The broken power law and log-normal models both fit the observed data relatively well, aligning well with Milky Way–derived IMFs. All in all, they find solid evidence for an invariant IMF in the early universe.

However, they are unable to say with absolute certainty that the IMF is invariant. Given that their data are nearly perfect (that is, it’s pretty much impossible to get better data for Boötes I), the authors emphasize that a larger sample of UFD IMFs is needed to truly rule out an invariant IMF, but we’re certainly taking steps in the right direction! As the age-old saying goes, “more data are needed!”

Original astrobite edited by Maggie Verrico.

1. Editor’s Note: The Milky Way IMF may vary from star cluster to star cluster; as described in this AAS Nova highlight from 8 July 2026, recent research using data from the Gaia spacecraft has found evidence for IMF variation in our galaxy. ︎

About the author, Drew Lapeer:

Drew is a first-year PhD student at the University of Massachusetts Amherst. They are broadly interested in the evolution of galaxies, with a focus on the impact of cosmic feedback on the galactic ecosystem. In their free time, they enjoy reading, rock climbing, hiking, and baking!

The post A Sneak Peek into Early-Universe Star Formation with Boötes I appeared first on AAS Nova.

Three-dimensional reconstructions of the Crab Nebula using oxygen emission lines. An animation of the 3D reconstruction is also available. [Ding et al. 2026]

Citation

“3D Kinematic Reconstruction of the Crab Nebula That Includes the Northern Ejecta ‘Jet,'” Z. Ding et al 2026 ApJ 1007 130. doi:10.3847/1538-4357/ae84c0

The post Featured Image: Evolution of a Cosmic Crab appeared first on AAS Nova.

X-ray absorption observations toward a black hole transient reveal the interstellar dust grain composition along the line of sight: a silicate magnesium-rich amorphous pyroxene and metallic iron.

The post Dust Grain Chemistry in the Diffuse Interstellar Medium Toward the Black Hole Transient GX 339–4 appeared first on AAS Nova.

While our solar system sports one Jupiter-like planet, exoplanet discoveries have revealed that giant planets come in a few different forms in systems with varying architectures. A recent study has explored how the mass–eccentricity relationship in warm Jupiters is shaped by dynamical interactions between planets.

Jupiter-like Planet Eccentricities

Exoplanet surveys have uncovered three different Jupiter-like planet populations across the galaxy: hot, warm, and cold Jupiters. Much like our own, cold Jupiters orbit on long periods, far away from their host stars. Conversely, hot Jupiters zip around their host stars on extremely short-period orbits. Somewhere in between, warm Jupiters orbit their host stars with periods from 10 to 365 days.

Diagram showing examples of a circular and an eccentric orbit. Click to enlarge. [AAS Nova/Lexi Gault]

Does this relationship extend to shorter-period giant planets as well? Hot Jupiters are heavily impacted by tidal interactions with their host stars, circularizing their orbits and erasing dynamical imprints on their eccentricities. Warm Jupiters, on the other hand, orbit far enough away for their eccentricities to preserve clues about their energetic histories. Recently, thanks to the Transiting Exoplanet Survey Satellite (TESS), astronomers have identified a positive correlation between planetary mass and eccentricity in a growing sample of warm Jupiters, but the exact driver of this trend has yet to be uncovered.

Planets Scattering Planets

To test if the positive mass–eccentricity correlation in warm Jupiters is consistent with planet–planet scattering, Jiayin Dong (University of Illinois at Urbana-Champaign) constructed a sample of 85 warm Jupiters from the NASA Exoplanet Archive. This carefully selected sample, dominated by discoveries from TESS and Kepler, included planets with masses between 0.3 and 15 Jupiter masses and orbital periods between 10 and 365 days. In conjunction with this sample, the authors built a planet–planet scattering framework to assess the range of properties anticipated for scattered warm Jupiter systems.

Warm Jupiter eccentricity versus planet–star mass ratio (left) and semimajor axis (right). Click to enlarge. [Dong et al 2026]

The mass–eccentricity relation of warm Jupiters, the authors suggested, represents a transition from collision-dominated interactions among low-mass planets to ejection-dominated interactions among high-mass planets. For massive enough systems, scattering can excite eccentricities high enough to trigger the high-eccentricity migration responsible for moving hot Jupiters to their close-in orbits. Overall, this study suggests that warm Jupiters are not a distinct planet species, but instead may represent the shorter-period counterparts of cold Jupiters whose orbits are shaped by the same dynamical processes. Future observations expanding the sample of warm Jupiters and discoveries of additional planet companions will further uncover the links between hot, warm, and cold Jupiter systems.

Citation

“Planet–Planet Scattering Explains the Mass–Eccentricity Relation of Warm Jupiters,” Jiayin Dong et al 2026 ApJL 1007 L29. doi:10.3847/2041-8213/ae930e

The post Planets Scattering Planets in Warm Jupiter Systems appeared first on AAS Nova.

JWST has detected more than a dozen new candidate H II regions, despite extensive radio surveys of the region, and these observations suggest that infrared photons can escape even dense, dusty gas.

The post JWST’s First View of the Most Vigorously Star-Forming Cloud in the Galactic Center: Sagittarius B2 appeared first on AAS Nova.

A curious gamma-ray burst with ambiguous properties may have been caused by a giant flare from a magnetar, but this would make the event three orders of magnitude more energetic than others of its class.

The post An Unusual Short Gamma-Ray Burst with Properties Intermediate Between SGRB and Magnetar Giant Flare Populations appeared first on AAS Nova.

Editor’s Note: This article was co-written by Lucas Brown and Alexia Kubas, our 2026–2027 AAS Media Fellows. We’re excited to welcome Lucas and Alexia to the team and look forward to featuring their writing on AAS Nova regularly!

Planetary nebulae mark a key evolutionary phase for low- and intermediate-mass stars, but properties of the parent star are difficult to sleuth out. Researchers have discovered an extragalactic planetary nebula in the center of a star cluster, offering an unprecedented opportunity to trace planetary nebula properties to parent star stats.

The Puzzle of Planetary Nebula Progenitors

A planetary nebula, so named because the first ones discovered resemble the planet Uranus in a small telescope, forms when a Sun-like star runs out of fuel and sheds its outer layers, leaving a hot remnant core enveloped in a gaseous nebula. At higher masses, a different process kicks in: stellar cores can collapse to produce a chaotic burst of stellar material called a supernova. Where exactly the boundary should be placed between planetary nebula progenitors and supernova-forming stars remains an outstanding question in the field of stellar evolution.

Answering this question is challenging because once a planetary nebula becomes visible, the progenitor star’s transition into a hot, compact white dwarf is already underway, making it difficult to determine the star’s initial mass. For this task, researchers seek out planetary nebulae within open clusters — groups of stars that were born from the same molecular cloud and are roughly the same age — so that cluster characteristics can help piece together the progenitor puzzle. Since open clusters tend to be relatively young, they are also a great tool to probe planetary nebulae from more massive progenitors and explore the boundary between stars that produce planetary nebulae and those that go supernova.

Striking Gold

Open cluster AP 210 and planetary nebula M279 in the Andromeda Galaxy, as seen in archival Hubble observations. Click to enlarge. [Chen et al. 2026]

To make this identification, Chen’s team used archival Hubble Space Telescope and MMT data to examine the location of the planetary nebula candidate M279 within the Andromeda Galaxy. The researchers’ critical observation was that the nebula not only overlaps with the position of an open star cluster called AP 210, but it also has an estimated velocity that matches the velocity of other stars in the cluster. These associations, when combined, provide strong evidence that M279 originated within the cluster.

Color–magnitude diagram of stars in the open cluster AP 210. Colored dots represent stars, and the red line is the best-fitting isochrone, which was used to determine the cluster’s age. Click to enlarge. [Chen et al. 2026]

What’s My (Cluster) Age Again?

M279’s cluster origin has significant consequences for pinning down the properties of the progenitor star. First, stars in open clusters all form at roughly the same time — 90 million years ago in the case of AP 210 — allowing the authors to set a tight constraint on the progenitor’s age. Then, because the rate at which a star burns through its nuclear fuel and generates a planetary nebula is related to its initial mass, the researchers are able to connect this age to a specific progenitor mass of around 5.7 solar masses.

The team also subtracted the central star’s contribution from the observed spectrum to isolate the nebula’s composition, illuminating specific nuclear processes relevant to higher-mass stars. Planetary nebulae are cosmic cocktails whose chemical abundances trace the composition of the interstellar medium when the progenitor formed as well as elements formed via nucleosynthesis inside the star during its lifetime. Chen and collaborators found the nebula to be significantly nitrogen-enhanced, which is consistent with a massive asymptotic giant branch progenitor undergoing hot bottom burning that converts carbon to nitrogen. This newly minted metal would then be mixed back into the star’s outer layers, flooding the resultant nebula with its particular spectral signature.

While this work represents only a single observation of a high-progenitor-mass planetary nebula — and only the third compelling extragalactic planetary nebula–open cluster pair — it opens up the possibility that there may be many more waiting to be found, unlocking new insight into the lives of massive stars.

Citation

“A Planetary Nebula from a 5.7 M_⊙ Progenitor in a 90 Myr M31 Star Cluster,” Pinjian Chen et al 2026 ApJL 1005 L2. doi:10.3847/2041-8213/ae77e4

The post Extragalactic Planetary Nebula with Massive Progenitor Sheds Light on Stellar Evolution appeared first on AAS Nova.

No bursty radio emission characteristic of star–planet interaction was detected from a sample of five M dwarfs with close-in terrestrial planets, but researchers were able to place limits on the magnetic fields of the planets.

The post Upper Limits on Planet-Induced Gigahertz Radio Emission from Inactive M Dwarfs appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: The Exozodi Spectral Effect: Residual Habitable Zone Dust May Bias exoEarth Characterization
Authors: Miles H. Currie et al.
First Author’s Institution: NASA Goddard Space Flight Center
Status: Published in AJ

Figure 1: Zodiacal light as seen from Cerro Paranal. [ESO/Y. Beletsky; CC BY 4.0]

This zodiacal dust is not exclusive to the solar system. Other star systems, such as Tau Ceti and Vega, have been found to host similar clouds of interplanetary dust. This means planets imaged in these systems will also have emission from this dust mixed into the light that we observe from the planets. The Habitable Worlds Observatory (HWO) is a future space telescope mission under development by NASA. One of its primary science goals is to directly image 25 Earth-like planets in the habitable zones of nearby stars and look for signs of life (or biosignatures) in these planets’ atmospheres. Exozodiacal dust (aka exozodi) represents the biggest source of astrophysical noise that will need to be subtracted out from HWO observations of exoEarths. The authors of today’s article look at the potential impact of exozodi emission on the spectra of exoEarth atmospheres.

Figure 2: Different models of three “zodis” of dust observed at an inclination of 60 degrees plotted across HWO’s potential wavelength range. The gray scattering model is shown in green, the solar system’s model is shown in black, with the red and blue debris disk models shown in their respective colors. The top panel shows the flux contrast between the dust and the star. The middle panel shows the flux per area. The bottom panel shows the total flux captured with a 7.2-meter HWO with the thin blue line representing the spectrum of an Earth twin 10 parsecs (33 light-years) away for comparison. [Currie et al. 2026]

Show Me the Zodi

The authors first assume four different models of exozodi dust and how the dust’s emission changes with wavelength. The first model assumes a dust cloud that acts as a gray scatterer, meaning the particles scatter all wavelengths of light with no preference, and the second model’s dust acts just like the solar system’s does. However, it’s unknown whether the composition of exozodi will be the same as the solar system’s. Therefore, they adopt two more models of exozodi that act just like debris disks that have different compositions. One model is bluer in color because it is made up of smaller particles that preferentially scatter blue light, and the other model is redder in color because it is made up of bigger dust particles or different chemical compositions. Each of these models over HWO’s wavelength range can be seen in Figure 2. The authors then simulate a modern Earth atmosphere (both clear and 50% cloudy) as well as an Archean Earth atmosphere to understand how different exozodi models will affect observations of different exoplanet atmosphere conditions and compositions.

There’s Dust in My Spectra

In general, the effect that zodiacal dust has on the spectra of Earth-like planets can be broken down into two categories: its effect on the continuum and on the spectral features. The continuum is the object’s light emitted over all wavelengths and uninterrupted by spectral features. Spectral features are absorption and emission lines. These create either a dip or peak in the spectrum where atoms have either absorbed or emitted light at that particular wavelength. Lines at specific wavelengths tell us that a certain material is there, providing a list of possible chemicals that could be present in the planet’s atmosphere. For a brief summary of spectroscopy more generally, see here.

In the case of the continuum, exozodiacal emission raises the continuum, meaning the base flux of the planet is raised and absorption lines become more shallow. These effects can be seen in Figure 3, where the authors’ simulated spectra are plotted with and without zodiacal dust included. Not only is the continuum elevated for all models including zodiacal dust, notice how the dips become shallower at longer wavelengths. Because dust primarily radiates thermally, the red debris disk model nearly smooths out all dips beyond 1.25 microns! Molecules that absorb at these longer wavelengths, such as water or methane, may not be correctly identified with this type of exozodiacal emission.

Figure 3: Spectra of simulated modern-Earth atmospheres for clear (solid bright lines) and cloudy (solid dimmer lines) scenarios. The Archean Earth atmosphere is plotted in dotted gray. The redder exozodiacal spectrum has an elevated continuum and smoothed spectral features as opposed to the original, zodi-free spectrum plotted in black. [Currie et al. 2026, with annotations by Kaz Gary]

From Figure 3, the effects of zodiacal dust are minimized with a bluer zodiacal dust model. This means systems with “bluer” zodiacal dust may be more optimal for HWO observations, as bluer dust does not scatter as much starlight as gray, solar system–like, or red dust. From their results, the authors recommend that the residual exozodi-to-planet flux ratio (in the V-band wavelengths) be kept to less than 10^-2 in order to correctly understand the line depths (identify if a molecule is present or not) and 10^-3 in order to accurately retrieve molecular abundances (understand how much of a molecule is present in the atmosphere). Dust is pesky enough here on Earth, but to find life on another planet like ours, we’ll dust have to deal with it.

Original astrobite edited by Anavi Uppal.

About the author, Kaz Gary:

I am a fourth-year PhD candidate at The Ohio State University with a passion for planets. My current work focuses on modeling exoplanet observations for the Habitable Worlds Observatory and understanding planetary atmospheres. Outside of research, I help develop planetarium shows and love all forms of science communication. In my free time, I enjoy playing tabletop RPGs, painting, watching terrible reality TV, and hanging out with my pet hedgehog.

The post Dust Deal with It appeared first on AAS Nova.

For nearly three decades, the Sloan Digital Sky Survey has collected photometric and spectroscopic data for millions of objects; this article describes the most substantial data release to date for SDSS-V.

The post The Nineteenth Data Release of the Sloan Digital Sky Survey appeared first on AAS Nova.

In 2017, we announced a new AAS-sponsored program for graduate students: the AAS Media Fellowship. This quarter-time opportunity is intended for current graduate students in the astronomical sciences who wish to cultivate their science-communication skills. This year, for the first time, we are welcoming two Media Fellows to the team.

We are pleased to announce that Lucas Brown and Alexia Kubas have been selected as our AAS Media Fellows for 2026–2027.

Alexia Kubas, a 2026–2027 AAS Media Fellow, is a graduate student at Cornell University.

Alexia majored in astronomy with minors in physics, math, and planetary sciences at the University of Arizona. They are now a fifth-year PhD candidate at Cornell University, researching periglacial processes on Earth and Ceres. Outside of research, Alexia founded and currently helps run an Ithaca, NY, chapter of Astronomy on Tap.

Lucas majored in physics with an astronomy concentration at the University of California, Davis, and he has a master’s degree in physics from Tufts University. He is now a physics PhD candidate at the University of California, Santa Cruz, where he works with Stefano Profumo on studying the phenomenology of primordial black holes. Outside of research, Lucas participates in outreach activities through organizations like the Santa Cruz Organization for Outreach in Physics and the Project for Inmate Education. He also serves as co-chair of the Astrobites collaboration.

2026–2027 AAS Media Fellow Lucas Brown is a graduate student at the University of California, Santa Cruz.

As AAS Media Fellows, Alexia and Lucas will regularly write and publish summaries of the latest astronomy research on AAS Nova, assist in managing the distribution of press releases as part of the AAS press office, and gain a broad understanding of the worlds of scientific publishing, communications, and policy. Alexia and Lucas will also be assisting with the press conferences at the upcoming AAS meetings, so please say hello if you spot them at future meetings!

As we welcome our new Fellows to the team, we’ll also soon bid farewell to Lexi Gault, our 2024–2026 AAS Media Fellow. Lexi will be continuing her PhD research at Indiana University, where she studies the interstellar medium conditions in nearby low-mass galaxies. After defending her PhD in Spring 2027, Lexi plans to pursue a postdoc in extragalactic astronomy or a full-time science writing position.

Please join us in welcoming Lucas and Alexia as our new Media Fellows and wishing Lexi the best in all her future endeavors!

The post Welcome and Farewell to Our AAS Media Fellows appeared first on AAS Nova.

A uniform analysis of crater catalogs finds that practically all computer-generated catalogs return worse metrics than manually generated catalogs, though most catalogs do well in some areas and poorly in others.

The post A Comparison of Lunar AI-Based Crater Databases Using Uniform Criteria appeared first on AAS Nova.

For decades, astronomers have tried to decipher the source of carbon oxides on Uranus’s largest moons from ground-based telescopes. A recent study has leveraged JWST spectroscopy and laboratory experiments to identify carbon oxides and their origins for Ariel, Umbriel, Titania, and Oberon.

Unknown Origins of Carbon Oxide Enrichment

Forty years ago, the Voyager 2 spacecraft flew past Uranus and its twenty-seven moons, sending back prized portraits of the planet’s large and tidally locked satellites Miranda, Ariel, Umbriel, Titania, and Oberon. These images revealed extensive valleys, smooth plains, deep canyons, and possible icy volcanic (cryovolcanic) activity across the surfaces of the icy moons — the telltale signs of intense geologic activity. While Voyager 2 could take spectacular pictures, the spacecraft was not capable of identifying the molecules and materials making up these active surfaces.

Voyager 2 images of Uranus’s six largest moons. Click to enlarge. [NASA / JPL-Caltech / Ted Stryk; CC BY-NC-ND 4.0]

Ground-based detections are limited due to contamination from Earth’s atmosphere as well as the overall weakness of the carbon dioxide spectral features, thus space-based near-infrared observations of the Uranian moons are necessary to better constrain the carbon oxides on the satellites. Luckily, JWST’s Near-Infrared Spectrograph (NIRSpec) now offers astronomers unimpeded access the moons’ carbon oxide spectral features.

Chemical Clues from Space and in the Lab

In 2024, a study acquired NIRSpec observations of Uranus’s moon Ariel, revealing prominent carbon dioxide features and confirming the presence of carbon monoxide ice hinted at by ground-based studies. Expanding on these observations to include Umbriel, Titania, and Oberon alongside Ariel, Richard J. Cartwright (Johns Hopkins University) and collaborators obtained JWST NIRSpec spectroscopy of Uranus’s four largest moons in hopes of disentangling the origin story of their carbon oxides.

Diagram illustrating the leading and trailing sides of a moon orbiting Uranus. Click to enlarge. [AAS Nova/Kerry Hensley]

Spectral ratios of the trailing and leading hemispheres for each moon, labeling spectral features of multiple carbon-bearing molecules. Click to enlarge. [Cartwright et al 2026]

Carbon Oxide Origins

What does this mean for the origins of the carbon oxides on the Uranian moons? Spectral features of carbonate minerals and the widespread presence of carbon dioxide throughout the Uranus system suggest that these compounds exist natively. On the other hand, the concentration of carbon oxide features on the trailing hemispheres supports radiolytic production as these hemispheres are bombarded with more ionizing particles from Uranus’s magnetosphere.

Based on these results, the authors have postulated that both origin scenarios, native presence and radiolysis, are required to fully explain the presence of carbon oxides. Future laboratory studies and JWST observations will continue to reveal the nature and composition of bodies in the Uranus system, furthering our understanding of our solar system siblings.

Citation

“Tracing the Source of Carbon Oxides on the Large Moons of Uranus,” Richard J. Cartwright et al 2026 Planet. Sci. J. 7 199. doi:10.3847/PSJ/ae8818

The post Breaking the Ice: Origins of Carbon Oxides on Uranian Moons appeared first on AAS Nova.

Three newly characterized microlensing events augment the growing list of events involving binary sources and lenses, emphasizing the importance of testing models of this complexity.

The post Four-Body Gravitational Microlensing Events Involving Both a Binary Lens and a Binary Source appeared first on AAS Nova.

Researchers have detected SO and SO₂ for the first time in an early-type evolved star; these results suggest that B[e]supergiants could be useful for studying sulfur chemistry under extreme radiation conditions.

The post Discovery of Sulfur Oxides in the Ejecta of a B[e] Supergiant appeared first on AAS Nova.

Light and dark regions speckle the Sun and other stars, complicating the interpretation of exoplanet transmission spectra. New modeling suggests that faculae — bright areas on the visible surface of the Sun — appear dark on cooler stars, adding a new wrinkle to this challenge.

Dark Spot, Bright Spot

This image from the Daniel K. Inouye Solar Telescope shows solar convective cells called granules. The bright points in the dark lanes between granules are regions of enhanced magnetic field strength. [NSO/AURA/NSF; CC BY 4.0]

The Sun is freckled with dark spots — sunspots — as well as bright regions called faculae. Sunspots form where the Sun’s magnetic field bubbles up, creating pockets of cooler, less luminous plasma. Solar faculae form in regions of concentrated magnetic field, creating bright spots that line the dark crevasses between convective cells.

Other stars also have starspots and faculae, but thus far, astronomers have no direct observations of faculae on any star except the Sun. Out of necessity, researchers interpreting exoplanet spectra assume that faculae on other stars are similar to those on the Sun — but are they actually?

Would a Facula on Any Other Star Look as Bright?

To explore what faculae might look like on stars other than the Sun, Alexander Shapiro (University of Graz; Max Planck Institute for Solar System Research) and collaborators turned to three-dimensional radiative magnetohydrodynamics simulations and radiative transfer modeling. Their aim was to simulate the appearance and spectra of faculae on stars of spectral type G2, K2, M0, and M4 — from Sun-like to substantially smaller and cooler than the Sun.

Simulated faculae on a Sun-like star (left) and an M4 star (right). These images show the faculae at 600 nm. Click to enlarge. [Shapiro et al. 2026]

Exoplanetary Effects

The transition from bright faculae on Sun-like stars to dark faculae on M4-class stars directly affects interpretations of exoplanet transmission spectra. The existence of dark faculae increases the derived exoplanet radius, whereas bright faculae on Sun-like stars decrease the derived radius. The contamination due to the faculae is wavelength dependent, with the largest contamination occurring at shorter wavelengths. This contamination, if not fully accounted for, can mimic spectral features from an exoplanet’s atmosphere.

Contamination of transmission spectra by faculae near a star’s poles (left) and closer to the star’s equator (right). Faculae are bright for the simulated G2, K2, and M0 stars, and they are dark on the simulated M4 star. Click to enlarge. [Shapiro et al. 2026]

Citation

“The Curious Case of Dark Faculae on M Dwarf Stars,” A. I. Shapiro et al 2026 ApJ 1008 24. doi:10.3847/1538-4357/ae7105

The post When Bright Spots Go Dark appeared first on AAS Nova.

Some systems in the Habitable Worlds Observatory (HWO) Exoplanet Exploration Program (ExEP) Mission Star List have more than a 50% chance of hosting a temperate terrestrial exoplanet.

The post Predictive Rankings of the Probability of Hosting a Temperate Terrestrial World for the HWO ExEP Mission Star List appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Thermal Electrons in the Radio Afterglow of Relativistic Tidal Disruption Event ZTF22aaajecp/AT 2022cmc
Authors: Lauren Rhodes et al.
First Author’s Institution: McGill University
Status: Published in ApJ

Tidal disruption events (TDEs, see Figure 1), which occur when a star gets a little too close to a supermassive black hole (SMBH) and gets ripped apart, are a hot topic across the electromagnetic spectrum. During a TDE, the star can no longer hold itself together under the gravitational pull of the SMBH. Some bits of the star end up accreting onto the black hole, which can launch a temporary outflow, or, in especially dramatic cases, a relativistic jet.

Figure 1: Timeline of events leading to a tidal disruption event. [Chloe Klare]

How to Spot a TDE

Usually, TDEs are discovered in the X-ray (after all, not many transients are powerful enough to generate an X-ray flare) or in the optical (thanks to high-cadence, wide-field surveys like the Zwicky Transient Facility and the Legacy Survey of Space and Time). However, radio is a particularly useful regime for TDE searches, especially in dusty host galaxies where we cannot see the optical TDE signatures at all; while dust obscures optical light, the radio is unaffected! There is just one catch: how exactly can we identify a TDE based on only its radio emission?

The radio light in a TDE is generated via synchrotron radiation — which is caused by fast moving electrons in strong magnetic fields — and originates in jets or shocks. Unfortunately, this is also the case in AGN, the primary extragalactic source of variable radio emission, and it can be difficult to distinguish between the two. Additionally, the amount of light we see from synchrotron radiation at a given frequency depends on how energy is distributed among the electrons in the source, which is unknown. Perhaps the simplest case — or at least the one you’ll learn about first in your undergraduate statistical mechanics course — is that the energy is distributed among the electrons thermally (left panel in Figure 2). However, most radio transients associated with black holes are assumed to have non-thermal electron energy distributions, usually where there are exponentially many more low-energy electrons than high-energy electrons (right panel in Figure 2).

Figure 2: Energy can be distributed among the electrons in a source either thermally (left panel), where most electrons have a medium amount of energy, or non-thermally (right panel), where most electrons have a small amount of energy. Often, extragalactic radio transients are assumed to originate from non-thermal electrons, but today’s article argues why we shouldn’t ignore thermal electrons. [Chloe Klare]

This includes today’s authors, who have focused on one particular TDE, ZTF22aaajecp/AT2022cmc (I’m sure everyone mispronounces her name), or 2022cmc for short. 2022cmc is a special TDE: it is one of only five TDEs suspected to have launched a relativistic jet, and it has the highest redshift (z ~ 1.2) of the five. It was observed first in the optical and then in the X-ray and radio. The X-ray emission was highly variable for 400 days post-TDE, and then disappeared, and the first 100 days of radio emission indicated there was a relativistic outflow. At the time, it was concluded that the jet shut off and the X-ray emission ceased. However, the story doesn’t end there; the authors of today’s article continued to observe 2022cmc in the radio for an additional 900 days at frequencies spanning about 1–100 GHz.

Our authors had two key observing strategies: wide frequency coverage and long duration. Measuring the change in brightness with observing frequency, or the spectral energy distribution (SED), is important for determining which processes are responsible for the radio emission, since thermal electrons and non-thermal electrons will produce different SEDs. On the other hand, measuring the change in brightness over time, or the light curve, is important for determining what is happening at the source, such as whether there is a jet and, if so, how long it lasts. Here, our authors combine light curves at six different frequencies (Figure 3) and SEDs at nine different epochs (Figure 4) to investigate both.

Figure 3: Light curves spanning six frequencies and 900 days obtained by today’s authors. [Rhodes et al. 2025]

Figure 4: Nine epochs of radio SEDs, which show the peak moving to lower frequencies over time. [Rhodes et al. 2025]

The Findings

Our authors find a couple of interesting results. First, in the time domain, they find the highest-frequency light curves fade with time, while the lower-frequency light curves increase initially, hit peaks at different times (after 300 days at 15.5 GHz, and after 800 days at 1.3 GHz), and then begin to decay. The spectral evolution is even more intriguing; the SED is always peaked, and the peak shifts to lower frequencies over time, which is typical for an expanding emission region. At frequencies below the peak, the SED doesn’t change much. However, the high-frequency side of the SED shows confusing behavior: early on, it has a very steep slope (the amount of light drops off sharply at higher frequencies), but it eventually flattens.

Investigations Begin

Next, our authors consider three possibilities to explain these observations. They first consider synchrotron radiation from only non-thermal electrons in a relativistic jet (Figure 5), which is the canonical model for a gamma-ray burst radio afterglow. Initially, the jet is so fast that all its radio light is relativistically beamed in one direction (like a flashlight), and we can only see the jet if it’s pointed directly at us. Eventually, the jet slows down enough that it is no longer beamed, and light is emitted in all directions (like a light bulb). At this point, we see the light fade over time, which is exactly what happened in the high-frequency light curves. However, there is one glaring problem: this model cannot possibly explain the observed long-lasting steep SED at high frequencies. So, our authors discard this theory.

Figure 5: The left image shows what a black hole–generated jet looks like in the rest frame of the jet itself. As long as the jet isn’t moving too fast, this is what we see too. However, if the material in the jet is moving near the speed of light, we observe a relativistically beamed jet (right image). [Chloe Klare]

Lastly, our authors keep the thermal/non-thermal electrons combo and ditch the jet entirely, modeling a spherical outflow. Excitingly, this model best fits the observations, and, most importantly, can explain the mysterious high-frequency behavior. Initially, most of the radio emission originates in the thermal electron population, which produces more light at higher frequencies. As the outflow expands, the non-thermal electrons begin to dominate, and the SED transforms into the classic non-thermal synchrotron shape.

Next Steps

Ideally, our authors want to compare 2022cmc to other TDEs, but few TDEs have such thorough follow-up observations. They speculate that thermal electrons were important in the radio evolution of one of the few such TDEs, Swift J1644, and recommend we revisit its emission models. More broadly, they recommend two future priorities: first, we need extensive radio observations for larger samples of TDEs, especially around 100 GHz, where the thermal electrons contribute most to the SED; secondly, we should stop neglecting thermal electrons not just in TDE models, but in models of any black hole jets, including gamma-ray bursts and X-ray binaries. While this work addresses only one event, one thing is clear. For theorists and observers alike, there is a myriad of exciting work to be done, so it’s no wonder TDEs have garnered so much attention lately.

1. A convenient property of extragalactic synchrotron sources is that all their electrons radiate independently of one another, even if they are part of the same electron population. This is called incoherent emission. (Galactic sources are another story, but I’ll save that for another time.) ︎

Original astrobite edited by Flavia Pascal.

About the author, Chloe Klare:

I’m a PhD student in astronomy and astrophysics at Penn State (with a physics minor, so I get to use my semester spent in QFT for something!). I study active galactic nuclei (in the radio!), and I’m currently looking for baby synchrotron jets in active galactic nuclei.

The post Thermal Electrons Can Explain the Mysterious Radio Behavior of a Tidal Disruption Event appeared first on AAS Nova.

More than half of solar magnetic flux appears to emerge in three bands, two of which rotate faster than the Carrington rate; this finding suggests a connection between surface flux and interior dynamical processes.

The post Long-Term Clustering Pattern of Solar Active Regions and Their Potential Connection with Magneto-Rossby Waves appeared first on AAS Nova.

A planned flagship spacecraft to Uranus was aiming to use Jupiter for a gravitational boost to shorten its journey to the outer solar system. Now that the mission’s launch date has been pushed back, it’ll need to find another way to its target.

Redesigning the Route

Uranus and Neptune, the ice giants of our solar system, have been comparatively neglected by humanity’s fleet of interplanetary probes. While all of the other major bodies have been visited by at least an orbiter or even a lander, the most detailed exploration we’ve done of these two planets happened when the Voyager 2 spacecraft went screaming past on its way toward interstellar space.

Schematics of different trajectories within the solar system. Left: The path the Galileo spacecraft took to Jupiter. This path arrived nearly parallel to the planet’s motion. Right: One of the proposed paths to Uranus. This path will intersect the planet’s orbit at a much steeper angle to shorten the flight time. Click to enlarge. [Simon et al. 2026]

Getting these spacecraft to their destination will be a challenge The thriftiest path to get to Uranus, a trajectory called a Hohmann transfer that’s been used for other missions aimed elsewhere in the solar system, would take 16–17 years. Rather than accept the long wait, the original authors suggested that the mission instead fly toward Jupiter, using the giant planet’s massive gravitational tug to slingshot the spacecraft toward Uranus.

However, this plan relied on Jupiter being in just the right place when the spacecraft approached. This in turn relied on the mission launching sometime in 2031 or 2032: any earlier or later, the slingshot would be aimed in the wrong direction. Now that timelines and budgets have slipped for this flagship mission, hitting this launch window seems unlikely. And, without the boost from Jupiter, the mission will have to cross 20 au of open interplanetary space on its own.

Solar Electric Propulsion to the Rescue

Several proof-of-concept designs for the mission’s SEP components. How these designs would be packaged into a rocket fairing for launch is shown at right. Click to enlarge. [Simon et al. 2026]

The power levels would likely get too low just a few astronomical units into their journey, but that would be enough: after discarding the SEP stage, the mission could coast to Uranus on a journey that would take only 13 years. Even better, this technology has a proven flight history and would require little maturation or development. The BepiColombo mission to Mercury is currently using SEP, and similar techniques are used on satellites in Earth orbit today.

Simon and collaborators also took on a number of other challenges that have cropped up since the mission was proposed, including fewer available plutonium power sources and a re-assessment of Uranus’s rings that revealed hazards in the original flight path. Their work brings the mission closer to the launch pad and illustrates how much iteration goes into the spacecraft that finally takes to the stars.

Citation

“Uranus Orbiter and Probe: Mission Challenges and Concept Updates Since the Origins, Worlds, and Life Decadal Survey,” Amy A. Simon et al 2026 Planet Sci. J. 7 143. doi:10.3847/PSJ/ae680c

The post Who Needs Jupiter? appeared first on AAS Nova.

Researchers have identified six new candidate circumbinary disk systems, potentially greatly increasing the number of known systems of this type; these system exhibit deep and prolonged dimming episodes.

The post Six New Circumbinary Disk Occultation Candidates from the Zwicky Transient Facility appeared first on AAS Nova.

Ultra-hot Jupiter KELT-9b possesses an outflow with a mass-loss rate above 10¹³ g s^-1 — one of the highest mass-loss rates measured for a gaseous exoplanet — and a diagnostic hydrogen Balmer line from its dayside.

The post Hydrogen Airglow from an Escaping Ultrahot Jupiter Atmosphere appeared first on AAS Nova.

While previous investigations of planet formation across the universe’s history suggest that planets trickled into the picture, a recent study has found that primordial planetesimals could have formed much earlier from the insides of the first stars in the universe.

First Stars, First Planets?

When the first stars flickered on, the universe was filled with pristine gas, containing only hydrogen, helium, and a little lithium. This gas, though great at making massive stars known as Population III (Pop III) stars, was not yet enriched with the heavy elements necessary for planet formation and, of course, life. Past studies have suggested that planet formation in the universe was gradual, taking several billion years to peak after billions of stars created and spilled the needed metals into the universe. However, local pockets of enriched gas from Pop III stars could have created the right conditions for planet formation earlier in the universe’s history.

Pop III stars burned bright and fast, exploding violently in pair-instability supernovae that completely shredded the progenitor, ejecting over 100 solar masses of metals into their previously pristine surroundings. Cosmological simulations suggest that oxygen from these supernovae could have produced significant water fractions within the dense cores of the supernova remnant. This may have set the stage for planet formation in water-rich disks around subsequent generations of stars as early as 150–200 million years after the Big Bang — does numerical modeling support this planet formation hypothesis?

Simulation snapshots showing the formation and evolution of the protoplanetary disk for 13, 21, 30, 40, 50, and 60 thousands of years after protostellar birth. Click to enlarge. [Modified from Vorobyov et al 2026]

Primordial Planetesimals in Simulated Water-Rich Disks

To test if these water-rich dense cores within Pop III supernova remnants could form planetesimals, the building blocks of terrestrial planets, Eduard I. Vorobyov (University of Innsbruck; Southern Federal University) and collaborators performed numerical simulations tracing the collapse of one such gas core into a protoplanetary disk around a protostar. The simulations begin from the gravitational collapse of a 1-solar-mass gas cloud core, with a protostar emerging 24 thousand years after the initial cloud collapse. As the protostar’s gravity pulled in material from its surroundings, a rotating disk formed around the growing star.

Simulation snapshot 40 thousand years after the formation of the protostar showing the gas, dust, and planetesimal surface densities and the dust-to-gas ratio. Click to enlarge. [Modified from Vorobyov et al 2026]

Citation

“Planet Formation at Cosmic Dawn: Planetesimals in H₂O-rich Disks around Low-mass Stars,” Eduard I. Vorobyov et al 2026 ApJL 1007 L51. doi:10.3847/2041-8213/ae907c

The post Primordial Planetesimals from the Guts of Population III Stars appeared first on AAS Nova.

Modeling of the Milky Way’s circumnuclear disk of molecular gas suggests that the gas is distributed in a disk with inner and outer radii of 1.0 and 2.9 parsecs and an inclination of 60 degrees.

The post Modeling the Milky Way Circumnuclear Disk: Rosettes and Rings appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: JWST Discovery of Warm Dust in the Circumgalactic Medium of the Makani Galaxy
Authors: Sylvain Veilleux et al.
First Author’s Institution: University of Maryland
Status: Published in ApJ

The Windy Galaxy

Billions of light-years away lies Makani, a record-breaking galaxy discovered in 2019 by researchers at the Keck Observatory atop Maunakea, Hawaiʻi. The galaxy shows evidence of a large merger event, where two galaxies collided to form a larger galaxy. This event triggered starburst activity, or several waves of intense star formation, that changed the makeup of not just Makani, but the region around it.

There are several processes that can create galactic winds. An active supermassive black hole at the center of the galaxy can slingshot particles out of the galaxy at close to the speed of light, or supernovae leftover from previous starburst activity can help to expel material from the galaxy. Makani, whose name in Hawaiian just so happens to mean “wind,” has both factors contributing to its galactic winds: massive amounts of star formation and a very active black hole in its center.

This contributes to some of the strongest galactic winds discovered to date, stretching approximately 100 kiloparsecs (330,000 light-years) beyond the galaxy, roughly ten times the extent of a typical galactic wind. These galactic winds remove gas from the galaxy and help to enrich the circumgalactic medium around the galaxy. There is still much to discover about how galactic winds change the makeup of such galaxies, and what exactly they take with them on their way out.

Earth’s Favorite Carcinogen: Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs, pronounced P-A-Hs or “paws”) are small flat dust grains scattered into every corner of the universe, from the atmosphere of Earth in the form of exhaust and wildfire smoke to the circumgalactic medium (the mostly empty space between galaxies). These PAHs contribute to regulating the temperature of the interstellar medium, but astronomers have long wondered how they migrate across galaxies.

Even though they are smaller than a human hair, PAHs are still easily observable even in very distant galaxies.  These dust grains emit infrared light, and if there are enough PAHs in a region, they are bright enough to be observed with modern telescopes, such as JWST. By combining multiple observations across multiple filters, astronomers can calculate ratios that reveal information about the PAHs’ size, temperature, and charge, allowing reserachers to further discern properties about the regions in which these PAHs reside.

With redshifted galaxies like Makani, the light from PAHs is stretched beyond its usual wavelength, but fortunately for today’s authors, the light was stretched just enough to land known PAH features well within JWST filters, as seen in Figure 1. The authors were then able to use this information to track the distribution of these PAHs across Makani.

Figure 1: Makani’s spectrum overlaid on top of the JWST filters. The peaks in the spectrum are PAH features that neatly overlap with JWST’s observing bands. [Veilleux et al. 2025]

PAHs Gone Extragalactic

Using JWST, the authors scrutinized Makani for any signs of PAHs. They found that not only did PAHs exist within the galaxy, these molecules were found up to 30 kpc (~100,000 light-years) outside the galaxy. Makani’s strong galactic winds were ejecting the dust grains from the galaxy over an estimated timescale of a billion years.

Previously, astronomers had not expected to find high quantities of dust grains outside the protection of a galaxy. The journey across a galaxy is long and hot, with temperatures in the millions of degrees. A dust grain would likely not survive the trip, as it would be destroyed by high-energy photons. This suggests that the PAHs were somehow shielded from the hotter parts of the interstellar medium and circumgalactic medium in large enough volumes to make it beyond the edge of Makani.

This answered questions about how galaxies enrich the circumgalactic medium, but it also added several more. Since today’s authors were limited by the sensitivity and range of their instruments, they were unable to confirm if there were PAHs along Makani’s entire wind structure, or just the first 35 kpc (114,000 light-years) of it. They also would like to turn their sights towards the intergalactic medium to see if PAHs could make it even farther beyond the reach of their host galaxy.

Original astrobite edited by Chloe Klare.

About the author, Natalie Price:

As a first-year master’s student at Wesleyan University, I study how stellar winds interact with the local interstellar medium. Outside of the observatory, you can find me dancing, with my nose in a book, or running at non-relativistic speeds.

The post Hitchhiking PAHs Caught Catching a Ride on Galactic Winds appeared first on AAS Nova.

Planets with radii 20% or possibly 30% smaller than Earth’s radius can maintain atmospheres, with initial carbon content, core radius fraction, initial mantle temperature, and other factors playing a role.

The post Smaller Than Earth Habitability Model (STEHM): The Lower Size Limit for Atmosphere Retention in the Habitable Zone appeared first on AAS Nova.

New observations of the coldest directly imaged planetary-mass companion of the pre-JWST era show a potential planetary formation pathway for the 25.2-Jupiter-mass object.

The post JWST-TST High Contrast: First Direct Spectroscopy of GJ 504 b Reveals Clouds and Possible Metal Enrichment appeared first on AAS Nova.

When a massive star collapses, the subsequent supernova can leave behind the star’s condensed core in the form of a neutron star. Some neutron stars are also pulsars, which rotate at incredible speeds, emit beamed radio emission, and expel winds of charged particles. A pulsar’s relativistic charged-particle winds billow around the pulsar as it travels through space — often at a few hundreds of kilometers per second or faster, having received a “kick” when its progenitor star exploded. When these winds interact with the surrounding supernova ejecta or the interstellar medium, the interaction creates a detectable pulsar wind nebula. The image above combines data from the Australian Square Kilometre Array Pathfinder (orange) and Wide-field Infrared Survey Explorer (cyan) to show a pulsar wind nebula, indicated with a white rectangle, within a larger supernova remnant. Sanja Lazarević (Western Sydney University) and collaborators discovered this pulsar wind nebula, which they’ve named “Thunder” in a nod to the supernova remnant’s moniker, “Nimbus.” The cometary shape of the pulsar wind nebula suggests that the pulsar is moving quickly, traveling outward from the center of the explosion that occurred some 30,000–45,000 years ago. To learn more about the discovery and characterization of this pulsar wind nebula, check out the article linked below.

Citation

“EMU Discovery of Thunder: A Bow-Shock PWN Powered by PSR J1631–4722 Escaping the Nimbus SNR (G336.7+0.5),” S. Lazarević et al 2026 ApJ 1007 159. doi:10.3847/1538-4357/ae7f11

The post Featured Image: A Pulsar in a Nebula in a Supernova Remnant appeared first on AAS Nova.

Astronomers have been measuring comets for centuries. But in December of last year, researchers collected a unique set of comet observations: they recorded some of the highest-quality data of one of the weirdest known comets while it was far from the Sun.

Simultaneous Spectra and Images

A few months after the famous interstellar comet 3I/ATLAS rounded the Sun and began its journey back into the space between the stars, a group of astronomers led by Nathan Roth (NASA Goddard Space Flight Center) aimed JWST in the direction of its retreat to watch it fade away. Using a special observing mode that leveraged the Integral Field Unit (IFU) in JWST’s Near Infrared Spectrometer, these observations didn’t result in just a single image of the comet, but a full stack of images, each corresponding to a different wavelength of light.

Using the IFU allowed the observers to combine the best of both regular imaging, which reveals spatial structure, and standard spectroscopy, which reveals wavelength dependencies. As a result, they could make spatially resolved maps of how the emission from the comet’s fuzzy atmosphere of gas and dust, or coma, changed with distance from the comet’s icy nucleus and angle to the Sun. Since different molecules radiate at different wavelengths, these maps in turn reveal the composition and geometry of 3I/ATLAS’s coma.

Mapping the Coma

The spectrum of the coma of 3I/ATLAS. Note that this is a real spectrum, not a simulation. The contributions of various molecules are labeled alongside their most prominent emission lines. Click to enlarge. [Roth et al. 2026]

First, in contrast with normal solar system comets where water is the most abundant molecule, water was actually a secondary player here: there was significantly more carbon monoxide, or CO, than water in 3I/ATLAS’s coma. The researchers note that this might not be representative of the true distribution of the two species, but instead be the result of the timing of these observations. When observing a standard solar system comet, astronomers usually examine their targets when the object in question is within 2 au of the Sun. At these close distances, solar radiation is strong enough that water ice dominates the outgassing and activity in a coma.

However, these IFU measurements were taken when 3I/ATLAS was about 2.4 au from the Sun, or right in the transition region where water doesn’t sublimate as easily as CO or carbon dioxide (CO₂). It’s likely that as the comet approaches the so-called “ice line” where water will naturally freeze out, CO will only increase its domination of the coma.

Top row: Maps of the distribution of various molecules in the coma. The white arrow shows the direction toward the Sun. Bottom row: The spatial distribution of the temperature of each species. Click to enlarge. [Roth et al. 2026]

Every Molecule for Itself

Second, each molecule seemed to be outgassing in its own unique direction from the coma. CO is leaving the nucleus in two different jets, one aimed directly back at the Sun and one perpendicular to it; CO₂ and methane (CH₄) are both leaking away in the anti-Sun direction; and water and methanol (CH₃OH) are sublimating in nearly spherically symmetric shells. The authors speculate that these geometries may be caused by different “active sites” on the comet, and that had they observed the comet for one full rotational period, they might have seen these jets pointing in different directions.

Although 3I/ATLAS is now too far and faint for observations like these, this study reveals just how much we can learn in the brief time interstellar visitors spend in our solar system. When the fourth interstellar comet inevitably wanders through the inner solar system, astronomers will doubtless be ready to use this observing mode again.

Citation

The post An Interstellar Comet’s Coma Composition appeared first on AAS Nova.

Recent radio rebrightening of a supernova observed in 2012 suggests that either the progenitor star experienced a past change in mass-loss rate or wind speed, or there is an off-axis relativistic jet present.

The post A 14-Yr-Old Mystery: The Peculiar Case of the Engine-Driven SN 2012ap appeared first on AAS Nova.

Gaia21bja is a young stellar object that brightens by up to 1.7 magnitudes during its outbursts, with its luminosity and mass-accretion rate increasing by a factor of 5.5–6 during the bursts.

The post Gaia21bja: Pre-Main-Sequence Star with Quasiperiodic Bursts appeared first on AAS Nova.

Using more than 50,000 images of coronal mass ejections, researchers have developed a novel machine-learning classification framework applicable to coronal mass ejections.

The post Automatic Detection and Segmentation of Coronal Mass Ejections in LASCO C3 Images appeared first on AAS Nova.

New research suggests that the circumplanetary disk surrounding the exoplanet PDS 70c contains a ring of dense dust, and the conditions within this ring may allow baby moons to form.

A Disk Within a Disk

A closeup of PDS 70c’s circumplanetary disk within PDS 70’s protoplanetary disk. [ALMA (ESO/NAOJ/NRAO)/Benisty et al.; CC BY 4.0]

There’s still debate over the exact source of the emission detected by ALMA. Does this emission come from dust, and if so, how is the dust distributed? Is the disk optically thick or optically thin? Does the emission even come from dust, or could it instead be free–free emission from unbound electrons navigating a charged-particle maze?

Dust Diagnosis

Yuhito Shibaike (Kagoshima University) and collaborators recently examined the hypothesis that the emission from PDS 70c’s circumplanetary disk arises from dust distributed in an optically thick ring. To test this hypothesis, the team explored two possible dust distributions, which they call “drift” and “ring.” In the drift model, dust grains within the circumplanetary disk migrate inward toward the planet, leaving much of the disk optically thin. Modeling suggests that this migration is typical in protoplanetary disks, and it might be common in circumplanetary disks as well.

Dust and gas surface density for the modeled disks in the drift (orange) and ring (blue) models. Click to enlarge. [Adapted from Shibaike et al. 2026]

Shibaike and coauthors found that the ring model naturally reproduced the observed spectral energy distribution for a range of reasonable parameters. The drift model, on the other hand, required an unrealistically high dust-to-gas ratio for the material accreted onto the circumplanetary disk from the parent protoplanetary disk to reproduce the observed spectral index.

Future Prospects and Moon-Making Possibilities

Comparison of ALMA observations (colored symbols) and model predictions (colored lines) from the drift (orange) and ring (blue) models. Click to enlarge. [Adapted from Shibaike et al. 2026]

Luckily, this likely won’t remain a mystery forever: the next-generation Very Large Array, which is anticipated to begin full science operations in the mid-2030s, should be able to resolve the location of the dust within the circumplanetary disk and illuminate the source of emission.

Finally, if the dust surrounding PDS 70c is concentrated within a ring, what does that mean for the possibility of moons forming within the disk? Shibaike and collaborators found that the conditions within the ring likely satisfy the requirements of both the streaming instability and the gravitational instability, which are required for dust grains to clump together and form the rocky building blocks of baby moons. Perhaps the PDS 70 system will one day be the site of not only a circumplanetary disk, but an exomoon as well!

Citation

“Interpreting ALMA Multiwavelength Continuum Observations of PDS 70 c: An Optically Thick Dust Ring in the Circumplanetary Disk,” Yuhito Shibaike et al 2026 ApJL 1006 L26. doi:10.3847/2041-8213/ae86f5

The post Probing Dust in the Disk of a Growing Giant Planet appeared first on AAS Nova.

By combining ground-based and space-based solar observations, researchers found that solar minimum solar wind predictions require higher source-surface heights than solar maximum predictions.

The post Source Surface Height Optimization for Improved Solar Wind Velocity Forecasting Across Solar Cycles 23, 24, and 25 appeared first on AAS Nova.

Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Unbreaking the Universe: MINERVA Measurements of Color Gradients in Massive Quiescent Galaxies Can Help Ease Too-Early Star Formation Tensions
Authors: Sam E. Cutler et al.
First Author’s Institution: Tufts University
Status: Published in ApJL

Universe Breakers

JWST launched in 2021, and one of its key goals was to observe the first galaxies as they formed. Early results from JWST found something surprising: extremely massive galaxies in the early universe that had “quenched,” or stopped making new stars, much faster than was expected. These early results led some to believe that our understanding of how quickly massive galaxies can form and quench was fundamentally wrong.

Before concluding that our understanding of the universe is broken, it’s important to find other reasons why we might see very massive galaxies in the early universe. One theory is that these galaxies are actually less massive than we think. To “weigh” a galaxy, astronomers first measure the amount of light being emitted by that galaxy. If all the light in a galaxy comes from stars (which should be true in the early universe, though active black holes can contribute a lot of light in some galaxies), you can infer the total number of stars by accounting for the average amount of light emitted per star of a certain mass; this is called the “mass-to-light ratio.” Since massive stars emit a lot more light than low-mass stars, and high-mass stars die out faster than low-mass stars, the mass-to-light ratio is higher for older stellar populations. To accurately “weigh” a galaxy, scientists therefore need both a good measurement of the total amount of light in the galaxy and how old its stellar population is. The authors of today’s article suggest that the uncertainty in these measurements might be leading to overestimates of galaxy masses and underestimates of galaxy star formation rates, possibly explaining the existence of the earliest massive quiescent (non-star-forming) galaxies.

The Impact of Color Gradients

Previous works about the massive quiescent galaxies in this study used spectroscopy to determine the galaxies’ masses and star formation rates. These spectra were taken with a “slit,” which introduces a source of error: if the slit is smaller than the image of the galaxy, some of the galaxy’s light will be missed in the spectrum. Astronomers usually correct for this by checking how much of the total light of a galaxy image is covered by the slit and scaling up the spectrum to account for the missing light, but this correction assumes that the spectrum is basically the same across the entire galaxy.

However, this assumption is rarely correct. In the local universe, star-forming spiral galaxies like the Milky Way tend to be made of a central “bulge” surrounded by a “disk” (see Figure 1). The bulge is no longer actively forming new stars, leading to a red-to-blue color gradient as you move out from the center of the galaxy. In astronomy, this is considered a “negative” color gradient. A slit that only covers the galaxy center would lead to an overall overestimate of the stellar mass and underestimate of the star formation rate. If the galaxies instead had a positive color gradient, with more star formation in the center of the galaxy, the mass would be underestimated and the star formation rate would be overestimated. Galaxies with both positive and negative color gradients have been found in the distant universe. By measuring the color gradient for each individual galaxy in their sample, the authors can correct the mass and star formation rate calculations from spectra taken with a slit spectrograph.

Figure 1: The spiral galaxy NGC 2683 with its bulge and disk labeled. The inner part of the galaxy (“bulge”) contains older, redder stars; the outer part of the galaxy (“disk”) contains bright blue stars that indicate that star formation is ongoing. Here, the slit spectrograph only covers the galaxy’s bulge, leading to incorrect mass and star formation rate measurements. [ESA/Hubble & NASA (CC BY 4.0) with annotations by Margaret Verrico]

Results

Instead of using spectra, the authors of today’s article use imaging in different filters to measure color gradients for a sample of four galaxies in the early universe that had previously been found to be extremely massive and no longer forming stars. They use medium-band filters, or filters that let in only a small part of a galaxy’s spectrum, to produce a spectral energy distribution at each radius. This spectral energy distribution is less informative than a spectrum (think a handprint versus a fingerprint), but it’s detailed enough to model the likely stellar population at each radius to determine whether the galaxies have positive, negative, or no color gradients, allowing for better corrections to the properties measured from the galaxies’ centers. They also model the stellar population from the central part of the galaxy that would normally be covered by a slit, as well as from the actual spectrum, to test whether any differences in their results come from their choice of modeling techniques.

The authors find that three of the four galaxies have a negative color gradient in at least some areas. The fourth galaxy has a relatively flat color gradient, though this measurement is less certain due to the object’s redshift. When the authors plot the galaxies’ colors on a diagnostic diagram that separates red and old galaxies from young and blue galaxies, they find that three of the four galaxies have centers that appear red and old but outskirts that appear young and blue (Figure 2). This means previous measurements of the mass may have been overestimated, and previous measurements of the star formation rate may have been underestimated.

Figure 2: The location of each of the four galaxies on a color–color diagram that separates red galaxies (above/to the left of the dashed lines) from blue galaxies (below/to the right of the dashed lines). The open markers indicate the galaxy color as measured from the center of the galaxy; the filled-in markers show the color at different radii from the galaxy center. For all but one galaxy, the color at several radii is bluer than at the center, indicating that the galaxy might have younger stars at least at some radii. [Adapted from Cutler et al. 2026]

Is the Universe Broken?

To determine whether these galaxies still count as “universe breakers,” the authors use a cosmological model to predict the largest expected galaxy mass in the observed area at different periods in cosmic time. The previous results had less than a 0.3% chance of occurring under current cosmological models; with their updated numbers and stellar population models, the authors find that the observed galaxies sometimes have more than a 5% chance of occurring, though there is still tension. They point out that their analysis ignores processes that could help galaxies grow and quench in the early universe, like galaxy mergers; still, the existence of these massive galaxies with such low star formation rates remains a puzzle.

Original astrobite edited by Ansh Gupta.

About the author, Margaret Verrico:

I am a fourth-year graduate student at the University of Illinois Urbana-Champaign. I study the connection between supermassive black hole transients and their host galaxies. I am also an avid knitter and reader, and I am passionate about opening up STEM opportunities for people of all backgrounds.

The post Galaxies of Many Colors appeared first on AAS Nova.

The supernova remnant W50 — nicknamed “the Manatee” because its blobby radio emission resembles an aquatic mammal floating through starry waters — harbors an extreme system at its heart. Near the center of the remnant, the microquasar SS 433 exhibits an immense pair of relativistic jets, likely powered by a stellar-mass black hole accreting material from a companion star. In the image of W50/SS 433 above, radio emission is in red, optical light is in yellow, and soft, medium, and hard X-ray emission are in green, cyan, and magenta, respectively. Brydyn Mac Intyre (University of Manitoba) and collaborators focused on the region circled above, using NuSTAR and XMM-Newton to understand the source of the X-ray emission in that region and the potential for SS 433 to accelerate particles to relativistic velocities. These observations suggest that W50/SS 433 accelerates electrons up to energies of more than 100 teraelectronvolts, and it may launch other particles into the highly sought-after petaelectronvolt range. To learn more about the particle-acceleration possibilities in this remarkable region, be sure to check out the full research article linked below.

Citation

“The Western Jet of SS 433/W50: Hard X-Ray Emission, Spectral Evolution, and Comparison to the Eastern Jet,” Brydyn Mac Intyre et al 2026 ApJ 1006 69. doi:10.3847/1538-4357/ae7a47

The post Featured Image: The Microquasar and the Manatee appeared first on AAS Nova.

The combination of gravitational wave emission, magnetic dissipation, and tidal interactions should cause the beat clock period of the CHIME/ILT J1634+44 system to change by tens of seconds per year.

The post A Falsifiable Timing Test for the Double-White-Dwarf Model of Long-Period Transients appeared first on AAS Nova.

Exactly how the universe became reionized after cooling to form stars and galaxies remains an open question. A recent study investigates how a merging set of galaxies may have spurred an onslaught of ionizing photons into the intergalactic medium.

Lyman Continuum Leakers and Merging Galaxies

After its chaotic and blistering beginning, the universe cooled and began to coalesce, stars and galaxies flickering on to set the universe alight. From a few hundred million to about a billion years after the Big Bang, galaxies pumped high-energy ionizing Lyman continuum (LyC) photons into the intergalactic medium during what is known as the epoch of reionization. The exact mechanisms that produced and allowed LyC emission to escape galaxies during this era remain elusive.

Hubble Space Telescope image of the interacting galaxy group Arp 194. The blue stream connecting the galaxies is where tidally stripped gas formed millions of new stars. [NASA, ESA, and the Hubble Heritage Team (STScI/AURA)]

While observational studies have increasingly pointed to galaxy mergers as considerable drivers of LyC escape, only a small number have explicitly considered the role of mergers in the epoch of reionization due to spectral and spatial resolution limitations. Leveraging the high-resolution capabilities of JWST, Shengzhe Wang (University of Chinese Academy of Sciences; National Astronomical Observatories, Chinese Academy of Sciences) and collaborators performed detailed analyses of two LyC-leaker candidates to better understand the role of galaxy mergers in heating up the universe.

Confirming (and Refuting) Merger-Driven Leaks with JWST

Using candidate LyC leakers first identified in the LymAn Continuum Escape Survey (LACES) carried out with the Hubble Space Telescope, Wang and team obtained high-resolution JWST spectroscopy for two galaxies at redshift z = 3.1 (about 2 billion years after the Big Bang), LACES94460 and LACES104037. After carefully identifying and measuring emission lines in each candidate, the authors confirmed LACES104037 as a merger-driven LyC leaker. However, the apparent LyC emission from LACES94460 was determined to be contamination from a low-redshift object.

Hubble and JWST observations of LACES104037. The top panels show the Hubble images (first two panels) and the JWST spectral observations (last three panels). The bottom panel shows a composite three-color image marking the location of two primary interacting galaxies and the LyC emission along with the associated spectra. Click to enlarge. [Wang et al 2026]

LACES104037-LyC represents the first confirmed LyC leaker of its kind: an external clump of star formation in a tidal tail. This discovery aids in our understanding of how mergers can drive high-energy photon emission, and highlights the critical role galaxy mergers may play in the epoch of reionization. Future high-resolution observations will hopefully reveal more knots of LyC-leaking stars within merging galaxies and provide a deeper understanding of this important evolutionary phase of the universe.

Citation

“Confirmation and Refutation of Lyman Continuum Leakers at z ~ 3 with JWST NIRSpec IFU,” Shengzhe Wang et al 2026 ApJL 1006 L17. doi:10.3847/2041-8213/ae8523

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Ultra-hot Jupiter WASP-121b is once again puzzling astronomers. New JWST observations have revealed aspects of this superheated planet’s atmosphere that models cannot yet explain.

An Extreme Planet

Among the more than 6,000 known exoplanets, there are many types of worlds that aren’t represented in our solar system. The most exotic and unfamiliar planets might be the ultra-hot Jupiters: giant planets nestled so close to their host stars that they are tidally locked, with temperatures on their permanently starlit sides climbing to thousands of degrees.

WASP-121b, which circles its F-dwarf host star every 30.5 hours, is one of the best-studied ultra-hot Jupiters. Previous work has started to reveal the complexity of its atmosphere, and now, data from JWST have opened a new window onto WASP-121b’s behavior.

New View from JWST

A representation of an exoplanet’s phase curve. Click to enlarge. [ESA]

The team used two 3D general circulation models to predict the planet’s atmospheric structure and extract synthetic spectra and phase curves to compare against the JWST observations. Using nine model configurations in total, the team varied several inputs, including sources of atmospheric opacity, sources of atmospheric drag, and assumptions about whether clouds are able to form on the planet’s cooler nightside.

Left with a Mystery

Frazier and collaborators found two aspects of WASP-121b’s phase curve that their models couldn’t explain: the planet emits less light overall than predicted, and the location of its phase-curve offset changes with wavelength.

Modeled phase curves, shown as the flux of the planet divided by the flux of the star, for WASP-121b (colored solid and dotted lines) compared to the best fit to the JWST observations (black line). Click to enlarge. [Frazier et al. 2026]

The phase-curve offset is the difference between a planet’s sub-stellar point (where the star is directly overhead) and the brightest point in the planet’s atmosphere. In general, some degree of offset is expected because planetary winds tend to whisk heat away from the sub-stellar point, placing the brightest point somewhere to the east (usually). For WASP-121b, the offset is unexpectedly small — suggesting a source of drag in the atmosphere that prevents winds from transporting heat away from the sub-stellar point — and it’s larger at shorter wavelengths. This wavelength dependence isn’t predicted by any of the models, and it’s not clear what causes it.

These results demonstrate something remarkable: that our observations of a planet nearly 900 light-years away have become so precise that they’re pushing our already complex models to include more physics — an exceptionally exciting motivation for model improvement!

Citation

“The Days Drag On on WASP-121 b: Interpreting Its NIRISS Spectroscopic Phase Curve with General Circulation Models,” Robert C. Frazier et al 2026 ApJ 1004 102. doi:10.3847/1538-4357/ae69ca

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In 2010, the supernova SN 2010jl illuminated a corner of a small, irregular galaxy 150 million light-years away. More than a decade later, researchers have found evidence that this collapsing massive star has created a significant amount of cosmic dust.

Superluminous Supernova

This X-ray and optical image shows SN 2010jl in its host galaxy. The supernova is the brightest X-ray source, near the top of the galaxy. [X-ray: NASA/CXC/Royal Military College of Canada/P.Chandra et al); Optical: NASA/STScI]

SN 2010jl offers an excellent chance to study the dust-forming potential of core-collapse supernovae. This supernova was unusually luminous because of intense interactions between the expanding supernova shock and the dense material surrounding the exploding star, and it’s possible that these types of interactions spur the creation of dust. In the first few years after the supernova was discovered, researchers found evidence that it had produced new dust. What has it been up to since?

SN 2010jl’s inferred dust mass over time (black stars) compared to other supernovae. Click to enlarge. [Smith et al. 2026]

Checking Back In

Thirteen years after SN 2010jl was discovered, Nathan Smith (Steward Observatory) and collaborators checked in on its dust production. The team collected new ground-based optical spectra from the Keck I telescope and the MMT Observatory and mid-infrared spectra from JWST. The optical spectra — among the latest collected for any superluminous supernova — show numerous narrow emission lines that indicate that the expanding supernova continues to interact with its surroundings.

In the JWST observations, SN 2010jl is the brightest mid-infrared point source in its host galaxy. Through spectral energy distribution modeling, Smith and coauthors found that the brilliant infrared emission is likely due to a shroud of warm dust totaling roughly 20% of the mass of the Sun. This is about 80 times more dust than inferred from observations made a decade earlier.

Where’s the Dust?

Diagram showing the outward-moving forward shock and inward-moving reverse shock of a supernova that is interacting with the interstellar medium (ISM). The post-shock region is located between the two shocks and contains shocked ejecta as well as shocked interstellar material. Click to enlarge. [AAS Nova/Kerry Hensley]

While it’s not possible to rule out the other options entirely, Smith and collaborators argue that at least some of the dust can be traced to new growth in the post-shock region. Because post-shock dust grains are likely to reach the interstellar medium, this suggests that superluminous, strongly interacting supernovae like SN 2010jl are a viable source of dust in the present-day universe and in high-redshift galaxies alike.

Citation

“JWST Spectra Indicate a Large Mass of Postshock Dust Formed by SN 2010jl,” Nathan Smith et al 2026 ApJ 1006 224. doi:10.3847/1538-4357/ae74c5

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Geometry, Not Calorimetry, Drives the Radio–Infrared–γ Ray Correlation
Authors: T. A. Porter, I. V. Moskalenko, and G. Jóhannesson
First Author’s Institution: Stanford University
Status: Published in ApJ

Galaxies emit light not only in the visible band, but also across other wavelengths via different physical mechanisms. Finding correlations between emissions at different wavelengths is a powerful tool for astrophysicists to explore the underlying mechanisms of galaxy formation. One of the most famous examples is the infrared–radio continuum correlation, which holds across several orders of magnitude in luminosity.

The typical explanation for this correlation is that both infrared light and radio synchrotron emission share the same energetic origin: star formation. Young stars emit ultraviolet radiation, which is absorbed by interstellar dust and re-radiated in the infrared. When these stars end their lives in core-collapse supernovae, the resulting shock waves accelerate cosmic-ray electrons, which then interact with the magnetic field to produce synchrotron emission.

For this correlation to hold, cosmic-ray electrons must radiate away all their energy within the galaxy, unable to escape and carry away some of their energy. Otherwise, the amount of radio emission would depend on how quickly cosmic rays escape and would no longer correlate with the infrared emission. This assumption is called the “electron calorimeter” model, which assumes that electrons lose all their energy due to radiation without escaping the galaxy. However, observations show that the infrared–radio correlation persists even in low-density galaxies where cosmic rays can easily escape, suggesting that the calorimeter model may not be the full story. To reconcile this, previous studies proposed “conspiracy-like” scenarios in which cosmic-ray injection, transport, magnetic-field amplification, and gas density are all coupled in a finely self-regulating way to maintain the correlation across diverse galactic environments — a somewhat awkward explanation that requires multiple unrelated physical processes to conveniently work together.

With the increased sensitivity of the Fermi Large Area Telescope, high-energy gamma-ray (or γ-ray) detections add new information to this picture. A galaxy’s γ-ray emission is produced by two different sources: cosmic-ray protons interacting with the interstellar medium gas, and cosmic-ray electrons inverse-Compton scattering off of nearby starlight or photons from the cosmic microwave background. Since both processes involve cosmic rays, the total γ-ray emission should also reflect the amount of star formation and therefore correlate with infrared and radio emission.

Because all three wavelengths trace different pieces of the same cosmic-ray population, studying them together reveals how the galaxy’s total cosmic-ray energy budget is distributed across its multi-wavelength emission.

The infrared–radio correlation has been established not only at the scale of entire galaxies, but also locally, down to patches roughly 100 parsecs across. Think of it like the relationship between a city’s electricity consumption and its population: we have long known they track each other city-wide, but it turns out the same relationship holds block by block. The infrared–radio correlation works the same way: zoom into any 100-pc region within a galaxy, and the correlation is still there. Unfortunately, the resolution of γ-ray observations is still stuck at around the kiloparsec scale. It is therefore unclear whether the local infrared–radio correlation reflects a genuine local physical coupling, one that would extend to γ-rays if we had sufficient resolution, or whether it is simply a spatial average of the emission, smoothed out by insufficient resolution. The answer determines whether radio and γ-ray emission can be used as reliable tracers of star formation, or whether they are just smeared out by cosmic-ray propagation over kiloparsec scales.

In this study, the authors numerically model galactic cosmic-ray transport, building a suite of physically motivated three-dimensional models of the Milky Way. They consider two variants for each of the four key inputs: 1) the cosmic-ray source distribution, 2) the interstellar gas, 3) the amount of starlight within the galaxy (the interstellar radiation field), and 4) the galactic magnetic field. Crucially, every model is normalized to reproduce the locally observed cosmic-ray data to within 5%, so that any differences in the predicted emission come purely from the large-scale geometry of each input, rather than from variations in the total cosmic-ray budget.

After evolving cosmic-ray transport for these realistic models, the authors then compute synthetic observations at radio, infrared, and γ-ray bands from various viewing inclinations to investigate how the underlying galactic model and the viewing angle affect the correlations between these emissions.

Surprisingly, inclination plays the most important role — more so than the cosmic-ray source distribution, the radiation field, or the magnetic field. Figure 1 shows the correlation plots between the radio and γ-ray emission (left two columns) and between infrared and γ-ray emission (right two columns) when viewing the galaxy face-on (i.e., viewing the galaxy from directly above the disk). Different colors represent γ-ray emission components from different physical mechanisms, with orange showing the total γ-ray emission. For both sets of correlation plots, starting from the upper-left panel, each panel modifies one physical input and recomputes the emission. Although there is some variation, one can see that the γ-ray emission correlates with both the radio and the infrared emission over several orders of magnitude, regardless of the underlying input model.

Figure 1: Radio (left two columns) and infrared (right two columns) vs. γ-ray correlation plots for a galaxy viewed face-on from 50 kpc. Each panel modifies one input — the cosmic-ray source distribution, gas, radiation field within the galaxy, or magnetic field — relative to a baseline model. Colors indicate γ-ray production mechanisms (green: proton–gas; black: inverse-Compton; orange: total). Across all variations, both the radio–γ-ray and infrared–γ-ray correlations remain quasi-linear over several orders of magnitude, showing that the correlations are robust to the choice of underlying galactic model. [Adapted from Porter et al. 2026]

In contrast, Figure 2 shows the correlation plot between radio and γ-ray emission (upper panels) and between infrared and γ-ray emission (lower panels) when viewing the galaxy edge-on (viewing the disk from the side). The radio–γ-ray correlation is preserved, while the infrared–γ-ray correlation is no longer observed. This is because, at this inclination, geometric projection separates the emission components. Infrared-emitting dust and γ-ray emission from cosmic ray–interstellar medium interactions are confined to the disk, while synchrotron radio emission and γ-ray emission from inverse-Compton scattering extend to larger distances above and below the disk. As a result, in an edge-on view, a sight line passing through the disk sees strong infrared emission, while a sight line that misses the disk sees zero infrared but still some γ-ray emission, breaking the infrared–γ-ray correlation. On the other hand, because radio emission is more extended than infrared emission, sight lines that miss the disk can still see both radio and γ-ray emission together, preserving the radio–γ-ray correlation.

Figure 2: Correlation plots for two galaxy models viewed edge-on from 50 kpc — simple axisymmetric (left) and complex with spiral arms (right). Top: radio vs. γ-ray; bottom: infrared vs. γ-ray. Colors indicate γ-ray production mechanisms (green: proton–gas; black: inverse-Compton; orange: total). The infrared–γ-ray correlation breaks down, while the radio–γ-ray correlation is broadened but partially preserved. [Porter et al. 2026]

However, there is one situation where the edge-on correlation comes back: when the observer is far enough away that the image becomes too blurry to resolve the galaxy’s internal structure. Figure 3 shows the same galaxy model viewed from 500 kpc, roughly the distance to Messier 31, our nearest large neighbor. At this distance, a single pixel in the image covers about 1 kpc, large enough for everything along the line of sight. The messy, broken-up pattern seen in the closer 50 kpc edge-on view (lower-right panel of Fig. 2) disappears, and a tight, nearly linear correlation comes back. This explains why nearly all distant, unresolved galaxies show tight radio–infrared–γ-ray correlations: the tightness is simply what you get when you blur everything together, not evidence that cosmic rays are actually losing all their energy locally inside those galaxies.

Figure 3: Correlation plots from a complex galaxy model viewed from 500 kpc, at three different inclinations (face-on, 45°, edge-on). Top row: radio vs. γ-ray; bottom row: infrared vs. γ-ray. Colors indicate different γ-ray production mechanisms (green: proton–gas; black: inverse-Compton; orange: total). At this distance, the blurring effect of large pixels restores a tight correlation even in the edge-on view. [Porter et al. 2026]

Now we have a consistent picture of the radio–infrared–γ-ray correlation: the authors conclude that this correlation is not a direct signature of cosmic-ray calorimetry, but a geometric projection effect. In face-on systems, a single sight line integrates emission from both the disk and off-disk regions, naturally producing a linear correlation, even when cosmic rays do not lose all their energy locally to radiation (i.e., local calorimetry is absent). In edge-on systems, the correlation breaks down because geometric stratification separates the different emission components. The practical implication is significant: for unresolved galaxies, the tightness of the global correlation alone cannot be used as evidence for cosmic-ray calorimetry, and the physically meaningful information about cosmic-ray transport and escape efficiency is encoded in the scatter around the mean trend, not in the correlation itself.

Original astrobite edited by Kelsie Taylor.

About the author, Sandy Chiu:

I’m a PhD candidate at the University of Michigan, Ann Arbor. I’m interested in numerical simulations of cosmic rays feedback in galaxies and their comparison with observation.

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Only one white dwarf star has ever been caught eating an asteroid. Recently, however, astronomers may have found another that just finished its meal.

Eating Asteroids

Although stars like our Sun don’t explode in violent supernovae like their massive counterparts, they don’t slink quietly into a peaceful old age either. When a solar-mass star reaches the end of its main sequence life, it first swells dramatically (the Sun may eventually grow so large that it consumes Earth and the device you’re reading this on), then shrinks down to a tiny but incredibly hot ember known as a white dwarf.

An artist’s impression of an asteroid breaking up near a white dwarf star. [NASA, ESA, M.A. Garlick (space-art.co.uk), University of Warwick, and University of Cambridge]

However, although researchers have found these stains in over a quarter of white dwarfs and consequently have reasoned that asteroid snacking must be common, they’ve only ever caught one star mid-meal. Recently, Ben Zuckerman (University of California, Los Angeles) and a team of collaborators may have found another, though it may have just finished dining.

Leftover Crumbs

The light curve of WD J0234-0406 measured by the Zwicky Transient Facility. Unlike WD 1145+017, which frequently changes brightness, this white dwarf appears remarkably steady despite the high-velocity gas surrounding it. [B. Zuckerman et al. 2026]

The researchers suggest that this relative quiet is a matter of timing. While asteroids are actively breaking up around WD 1145+017, the parent bodies that supplied the gas and dust around WD J0234-0406 may have shattered long ago and have already been either vaporized or ground down into smaller particles. All that is left over are the crumbs slowly spiraling toward the star.

Although WD J0234-0406’s meal may not be as dramatic as WD 1145+017’s feast, it’s still exciting to expand the sample of known white dwarf-asteroid interactions. And, with the upcoming release of data from the DESI survey poised to reveal the spectra of tens of thousands of white dwarfs, the sample is likely to grow again soon.

Citation

“High-velocity Circumstellar Gas Orbiting a White Dwarf Star,” B. Zuckerman et al 2026 ApJ 1004 254. doi:10.3847/1538-4357/ae23c4

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Even the darkest corners of the universe are not completely empty. A recent study has used fast radio bursts to provide the first estimate of the baryon content in cosmic voids.

What’s in a Void?

Cosmological studies have revealed the large-scale filamentary structure of the universe known as the cosmic web. Chains of galaxies and galaxy clusters fall into spindly strands (or filaments) of matter overdensities, opening up cavernous cosmic voids that comprise the darkest corners of the universe. These seemingly vacant voids serve as critical test beds for cosmology, allowing researchers to constrain things like the nature of dark energy and the matter density of the universe.

Despite their name, voids are not completely empty but are instead underdensities with considerably less matter compared to the bustling filaments they border. The baryon (normal matter) content of cosmic voids has important implications for cosmological models and large-scale galactic feedback processes, but assessing how many baryons actually occupy voids has only recently become observationally accessible.

Sky maps centered on the north celestial pole showing the CHIME fast radio burst sample (top) and the SDSS void catalog (bottom). [Sharma et al 2026]

Chiming In on the Baryon Search

In concept, directly stacking fast radio burst sight lines that coincide with the positions of known cosmic voids provides a direct measurement of the baryon underdensity inside voids. With no previous observational exploration of this quantity, Kritti Sharma (California Institute of Technology) and collaborators leveraged the second catalog of the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Bursts (CHIME/FRB) sample in conjunction with the Sloan Digital Sky Survey (SDSS) Baryon Oscillation Spectroscopic Survey (BOSS) void catalog to provide the first observational assessment of the baryon underdensity in cosmic voids.

Anticorrelations between fast radio burst dispersion measures and void positions. There is a clear dispersion measure deficit closer to voids centers. [Sharma et al 2026]

This study provides a unique approach to baryon mapping and opens up the door for future investigation of cosmic voids. While not physically containing much, voids hold vast astrophysical and cosmological significance. With the astronomical stage primed with galaxy-mapping powerhouses like the Dark Energy Spectroscopic Instrument, Vera Rubin Observatory, Nancy Grace Roman Space Telescope, and Euclid Space Telescope, cosmic voids will become a cornerstone of cosmological studies.

Citation

“Baryons in the Darkest Sites of the Universe,” Kritti Sharma et al 2026 ApJL 1006 L3. doi:10.3847/2041-8213/ae81ac

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: The JWST EXCELS Survey: Insights into the Nature of Quenching at Cosmic Noon
Authors: Maya Skarbinski et al.
First Author’s Institution: Johns Hopkins University
Status: Published in ApJ

How to Quench a Galaxy

Look at an image of the sky taken with a sufficiently sensitive telescope, and you’ll quickly notice that galaxies tend to cluster into two main types: blue spiral galaxies, which have flat disk shapes with a central bulge, and red elliptical galaxies, which look like spherical or elliptical balls of red stars. Blue spiral galaxies can form tens to hundreds of stars every year, while elliptical galaxies have completely stopped forming stars, meaning that some process has to transform star-forming spirals into non-star-forming, or “quiescent,” elliptical galaxies. To form the current population of massive elliptical galaxies, this process had to be common about 2–3 billion years after the Big Bang at “cosmic noon,” the period when star formation in the universe peaked. The processes that “quench” star formation in massive galaxies are still being studied, and one of the best ways to study them is to find galaxies that recently quenched and look for clues about the processes that quenched them.

Post-starburst galaxies are galaxies that have rapidly quenched after a short burst of star formation. Because these galaxies quenched so quickly and so recently, it’s often possible to find signs of whatever quenched them, like the signatures of past galaxy mergers, feedback from supermassive black hole accretion, or the shutoff of gas flowing into the galaxy. Rapid quenching is pretty uncommon now, but it was a much more common way for galaxies to quench at cosmic noon. Understanding post-starburst galaxies at cosmic noon is therefore critical for understanding the formation of massive elliptical galaxies in the local universe.

The Quest for Quenched Galaxies

Today’s article uses data from the JWST Early eXtragalactic Continuum and Emission Line Survey (EXCELS) to identify post-starburst galaxies at cosmic noon and try to determine why they quenched. EXCELS is a spectroscopic survey, so the authors get a spectrum for every galaxy. The spectrum encodes information about the galaxy’s stellar population, including the mass of stars in the galaxy, the number of stars forming every year, and the history of star formation throughout the galaxy’s life.

The authors use a technique called principal component analysis to further divide the sample into young and old post-starbursts. Principal component analysis is a machine-learning technique that learns the most important features of a data set. This technique is used for “dimension reduction,” or reducing the number of data points needed to learn something about the object. A typical spectrum has hundreds or even thousands of data points, which means performing data analysis on a spectrum can be very computationally expensive. Principal component analysis takes these thousands of data points and learns broad patterns that correlate with each other. These patterns are called “supercolors” in the context of spectral data, and they encode things like the overall shape and color of the spectrum as well as the spectral shape around key features (see Figure 1 for a visualization). Since the overall shape, color, and emission/absorption line features of a spectrum come from the galaxy’s stellar population, this method can be used to identify galaxies with lots of star formation a billion years ago but very little star formation today — in other words, post-starburst galaxies.

Figure 1: An example of principal component analysis for sample star-forming (SF), quiescent (Qu), and post-starburst (PSB) galaxy spectra (left-hand side). Principal component analysis simplifies a many-dimensional data set (for example, spectra) into fewer dimensions. In this case, Super-Color 1 measures the overall color of the spectrum (shown on the left-hand side as the slope of the spectra, marked with red lines), while Super-Color 2 measures the shape of the spectrum around 4,000 angstroms (orange box). The authors use principal component analysis to identify post-starburst galaxies for further analysis (right-hand side). [Adapted from Skarbinski et al. 2026]

The authors apply principal component analysis to the galaxies in their sample and find that 11 of the galaxies in their sample are classified as post-starburst, 9 are quiescent, and 4 still have some star formation. To further analyze the stellar populations of the post-starbursts in their sample, the authors use a program called Bagpipes to fit the galaxies’ spectra. Bagpipes is a spectral energy distribution fitting software, which means that it takes the observed spectrum of a real galaxy and tries to match it to a library of different stellar spectra. By measuring the relative contribution of different kinds of stars (which all have different lifetimes), Bagpipes can compute the likely history of star formation in the galaxy (e.g., when the star formation rate peaked) as well as the present-day properties of the galaxy (things like the mass in stars versus dust and the current star formation rate). The authors use the galaxies’ star formation histories to try to find clues as to how they quenched.

How Quickly Do Post-Starbursts Quench?

First, the authors measure something called a “quenching timescale,” which they define as the length of time between when the galaxy’s star formation rate peaked and when it fell low enough that the galaxy was quenched. The quenching timescale depends on which process shut down star formation in the galaxy — feedback from black hole accretion or star formation should cause fast quenching, while galaxies that are starved of gas from the intergalactic medium should quench more slowly. The authors find that 15 of their galaxies quenched in under 500 million years, 6 took between 500 million and 1 billion years, and 3 took longer than 1 billion years to quench. The galaxies that had the highest peak star formation rates quenched the fastest, suggesting that feedback from star formation could have played a role in quenching these galaxies.

Figure 2: Possible evolutionary tracks in supercolor for two example galaxies as they quench. The galaxy in the top panel quenches quickly and has post-starburst supercolors for about a billion years, while the galaxy in the bottom panel quenches without ever going through the post-starburst phase. The authors use these tracks to determine how important the post-starburst phase is for quenching massive galaxies. [Skarbinski et al. 2026]

Next, the authors measure how important the post-starburst phase is to form massive quiescent galaxies. Not all galaxies that quench go through a post-starburst phase; some objects, especially those that quench slowly, will transition directly from star forming to quiescent. The authors use the star formation histories from their spectral energy distribution fits to predict how the galaxies’ supercolors changed after their star formation peaked (Figure 2) and find that six of the nine quiescent galaxies went through a post-starburst phase in the past, while the other three did not. For the objects that went through a post-starburst phase, the median time spent as a post-starburst was around 600 million years.The authors can use this measured “visibility timescale” to constrain whether the post-starburst phase is important for forming massive quiescent galaxies. If the fraction of post-starburst galaxies in a sample is high, that can be for two reasons: either a larger fraction of galaxies will eventually go through a post-starburst phase, or the post-starburst phase is very long, making it easy to find post-starburst galaxies. Using the measured timescale of 600 million years and combining with results from another article, the authors find that 40% of quiescent galaxies likely went through a post-starburst phase; for the more massive end of the sample, this fraction increases to around 73% due to the shorter visibility timescale. This suggests that the post-starburst phase is very important for forming the kind of massive quiescent galaxies we see in the local universe.

While the post-starburst phase is important, the different quenching timescales present across the sample suggest that multiple pathways existed to quench galaxies at cosmic noon, similar to what has been found in less-distant galaxies and at cosmic noon in other samples. This is also supported by the fact that four of the five galaxies with sufficient data show evidence of an actively accreting supermassive black hole that may help shut down star formation in many (but perhaps not all) massive galaxies. While the precise processes that quench massive galaxies are still uncertain, one thing is clear: JWST EXCELS at solving the mystery!

Original astrobite edited by Anavi Uppal.

About the author, Margaret Verrico:

I am a fourth-year graduate student at the University of Illinois Urbana-Champaign. I study the connection between supermassive black hole transients and their host galaxies. I am also an avid knitter and reader, and I am passionate about opening up STEM opportunities for people of all backgrounds.

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During the 8 April 2024 solar eclipse, the path of totality swept across North America, dazzling millions of skygazers. Scattered along this path were 82 viewing sites of the Dynamic Eclipse Broadcast Initiative citizen science project, which aimed to observe the dynamics of the tenuous solar corona. Though poor weather dashed many observers’ hopes, the project managed to collect data at 11 sites spanning 2,700 kilometers, capturing 49 minutes of coronal behavior. The image above shows the solar corona as seen during totality from one of the DEB Initiative sites. In a recent research article, Matthew J. Penn (Southern Illinois University Carbondale; Tucson Amateur Astronomy Association) and collaborators described the results of the Initiative’s viewing efforts, including identification of downflows and outflows, plumes, coronal loops, and apparent motion of background stars. To learn more about these observations of the solar corona, be sure to check out the full article linked below.

Citation

“Structure and Dynamics of the Inner Corona Measured from the DEB Initiative 2024 Eclipse Image Sequence,” Matthew J Penn et al 2026 ApJL 1006 L25. doi:10.3847/2041-8213/ae8797

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Traversing through the solar system, a comet split in two, and a recent study used six months of observations to investigate when and why.

A Split Comet

Orbital path of 240P/NEAT (purple) and the position of the comet on 30 July 2026 (light blue teardrop). Click to enlarge. [TheSkyLive]

Most recently, 240P swept closest to Jupiter in July 2007, shifting the comet’s perihelion distance (closest approach to the Sun) from 2.5 to 2.1 au, and several long-lived bursts in brightness in 2018/2019 could have been spurred by this orbital shift. Excitingly, a fainter comoving object, 240P-B, was first reported in June 2025 as the comet headed toward perihelion — at some point recently, 240P had split in two!

Over the last century, numerous split comets have been recorded, but detailed physical studies of these objects are rare. With growing evidence suggesting splitting and disintegration are the primary mechanisms of comet destruction, understanding the properties and cause of 240P’s split is imperative.

Observing 240P

With 240P on the move to perihelion, David Jewitt (University of California, Los Angeles) and collaborators monitored the comet from October 2025 to April 2026 to establish the likely cause of its split. Employing the Alhambra Faint Object Spectrograph and Camera on the 2.56-meter Nordic Optical Telescope, the authors obtained detailed imaging of the comet from two months before to four months after perihelion to characterize both components.

Tracking both photometric and morphological changes across their observations, the authors estimated the dust-loss rates, physical sizes, and separation speed of 240P-A and 240P-B. The brighter component, 240P-A, has an estimated radius between 400 and 600 meters and a dust-loss rate almost four times higher than 240P-B. Because 240P-B is fainter, its radius is harder to constrain observationally. From its lower dust-loss rate and lower brightness, the authors estimated a radius around 300 meters (and no smaller than 50). Based on how the separation of the two comet pieces changes over time, the authors determined that the split of 240P occurred at least three years before their observations.

Dust mass-loss rates for 240P-A (green circles) and 240P-B (yellow diamonds) over the course of the observations. Both components peak shortly before perihelion (dashed vertical line). Click to enlarge. [Jewitt et al 2026]

Source of the Split

How exactly did this fragmented comet get this way? The authors considered a number of comet-splitting mechanisms: tidal forces, asteroid impact, pressure buildup below the comet’s surface, thermal stresses, and rotational instability. Given the comet’s orbit, it has not had close enough encounters with the Sun or other planets for tidal forces to be the culprit, and it traverses well above the asteroid belt, avoiding collisions. Pressure buildup and thermal stresses can fracture comets, but both are unlikely to launch such a large fragment as seen in this system.

This leaves rotational instability as the likely source of 240P’s split. Outgassing torques lead to rotational instability, especially in subkilometer comets like 240P, and 240P has exhibited recent outgassing. In addition, the separation speed between the 240P components is comparable to the escape speed of the primary comet, which is expected for rotational breakup. To confirm this hypothesis, future observations measuring the rotation period of 240P are necessary, but this study adds to the small number of split-comet observations that aid in understanding comet destruction.

Citation

“Investigation of Split Comet 240P/NEAT,” David Jewitt et al AJ 172 113. doi:10.3847/1538-3881/ae83ac

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A recent Focus Issue of the Astrophysical Journal Letters describes the fourth version of the catalog of gravitational wave events (GWTC-4.0) from the Laser Interferometer Gravitational Wave Observatory (LIGO), the Virgo interferometer, and the Kamioka Gravitational Wave Detector (KAGRA).

This catalog contains transient gravitational wave events recorded through January 2024, during the observatories’ fourth observing run, which concluded in November 2025. GWTC-4.0 displays the results of significant improvements to our suite of gravitational wave detectors, including higher-powered lasers and reduced quantum noise. A fifth catalog of gravitational wave events was released in Spring 2026, with the accompanying scientific articles being submitted to the Astrophysical Journal and the Astrophysical Journal Letters.

This Monthly Roundup consists of short descriptions of each of the currently published research articles in the LIGO–Virgo–KAGRA Gravitational Wave Transient Catalog (GWTC): Release 4 Focus Issue. Each snippet links to the corresponding research article, and the Focus Issue landing page is linked at the bottom of this post. Be sure to revisit the landing page to catch new articles as they’re published!

Introducing GWTC-4.0

A timeline showing observing runs between 2015 and 2024. Click to enlarge. [LVK Collaboration 2025]

After these detectors record subtle spacetime squiggles from compact objects colliding millions to billions of light-years away, the collaboration converts the raw signals into the data contained in catalogs like GWTC-4.0. This process involves modeling the gravitational wave signals, filtering them to identify candidate transients, and pinpointing the most significant events.

After collecting and cleaning the signals, the collaboration undertakes a critical step: making their data accessible to researchers and the public. The data are available through the Gravitational Wave Open Science Center, and the Focus Issue article on open data describes how to navigate the online portal, how the datasets archived online are structured, and how the data were calibrated.

Science Results

This fourth version of the gravitational wave transient catalog greatly expands the sample of gravitational wave transients recorded by detectors across the globe. Including events from previous catalogs, GWTC-4.0 brings us to 218 events for which the probability of the source being astrophysical in nature is more than 50% and for which there is little chance of the signal being an instrumental artifact. This represents a more than 100% increase in the number of recorded gravitational wave events fulfilling this criterion, broadening our understanding of colliding compact object pairs. This release also includes some superlative signals, such as the most massive black hole binary with a low false-alarm rate and the highest signal-to-noise ratio for a gravitational wave event thus far.

Detected in November 2023 by both LIGO Hanford and LIGO Livingston, GW231123 is in many ways an exceptional gravitational wave transient. The total mass of the merging components appears to be between 190 and 265 solar masses, and the false-alarm rate for this signal is less than one per year. This makes it the most massive merger event with such a low false-alarm probability. The two components also appear to have high spins, which complicates the interpretation of the signal with existing models. A binary black hole merger in which one or more components lies within the pair-instability mass gap is the likeliest explanation for this signal, but the authors also present alternative scenarios, such as a core-collapse supernova or a gravitationally lensed gravitational wave signal.

Representations of the GW230814 gravitational wave signal. Click to enlarge. [LVK Collaboration 2026]

Plot of the differential merger rate as a function of the mass of the more massive of the two merger components. This shows overdensities at 10, 35, and possibly 20 solar masses. Click to enlarge. [LVK Collaboration 2026]

The full list of articles in the GWTC-4.0 Focus Issue can be found here.

Citation

“GWTC-4.0: An Introduction to Version 4.0 of the Gravitational-Wave Transient Catalog,” A. G. Abac et al 2025 ApJL 995 L18. doi:10.3847/2041-8213/ae0c06

“GWTC-4.0: Methods for Identifying and Characterizing Gravitational-Wave Transients,” A. G. Abac et al 2026 ApJL 1004 L21. doi:10.3847/2041-8213/ae447b

“Open Data from LIGO, Virgo, and KAGRA Through the First Part of the Fourth Observing Run,” A. G. Abac et al 2026 ApJ 1004 232. doi:10.3847/1538-4357/ae211e

“GWTC-4.0: Updating the Gravitational-Wave Transient Catalog with Observations from the First Part of the Fourth LIGO–Virgo–KAGRA Observing Run,” A. G. Abac et al 2026 ApJL 1004 L22. doi:10.3847/2041-8213/ae2c74

“GW231123: A Binary Black Hole Merger with Total Mass 190–265 M_⊙,” A. G. Abac et al 2025 ApJL993 L25. doi:10.3847/2041-8213/ae0c9c

“GW230814: Investigation of a Loud Gravitational-Wave Signal Observed with a Single Detector,” A. G. Abac et al 2026 ApJL 1004 L23. doi:10.3847/2041-8213/ae2ad3

“GWTC-4.0: Population Properties of Merging Compact Binaries,” A. G. Abac et al 2026 ApJL 1005 L51. doi:10.3847/2041-8213/ae771e

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: The Rhythm of the ISM: Tracing the Timescales of Gas Evolution and Star Formation Across Galactic Environments
Authors: Zuzanna Kocjan and Vadim A. Semenov
First Author’s Institution: University of Maryland
Status: Published in ApJ

The Connection Between Gas and Star Formation in Galaxies

Stars are born in the interstellar medium (ISM) when cold, dense clouds of gas become unstable and collapse under gravity. Despite their plentiful reservoirs of gas, galaxies convert only a small fraction of this material into stars, making star formation a surprisingly inefficient process. A key factor behind this inefficiency is stellar feedback: radiation, stellar winds, and supernova explosions from young stars can inject energy and momentum into the surrounding gas, heating, stirring, and dispersing it. In this way, stellar feedback shapes future star formation across scales ranging from individual regions in the ISM to whole galaxies.

An important tool astronomers use to study star formation is the Kennicutt–Schmidt relation, which links the amount of gas in a galaxy to the rate at which stars form. More specifically, it relates the gas surface density, Σ_gas, to the star formation rate surface density, Σ_SFR. (For more on this relation, see this Astrobites article on a classic research article.) However, this law is underpinned by a crucial ingredient: timescales. In particular, the pace of star formation depends both on how quickly galactic gas is cycled into star-forming material and on how rapidly those regions convert gas into stars once they form. Today’s article investigates the physical origin of star-formation scaling relations behind the Kennicutt–Schmidt law by building on a simple theoretical framework for the ISM.

Consider a Kettle of Boiling Water…

In a given region of a galaxy, the ISM consists of gas in either an actively star-forming state or an inert, non-star-forming state, depending on whether it is dense and unstable enough to collapse (as illustrated in Figure 1). The transition of non-star-forming gas into the star-forming state occurs on the supply timescale, τ₊. Conversely, the dispersal of star-forming gas back into a non-star-forming state is characterized by the removal timescale, τ_–. As a helpful analogy, the authors compare this process to water boiling in a kettle: the ISM is continuously “boiling,” with gas moving between active and inactive states. Meanwhile, the total gas reservoir gradually decreases, analogous to water slowly evaporating as the kettle boils. The gas depletion time, τ_*, therefore represents the timescale over which the available gas would be exhausted by star formation.

Figure 1: Schematic of the gas cycling framework used in the authors’ theoretical model for how gas is converted into stars, which takes into account a supply, removal, and depletion timescale. [Adapted from Kocjan and Semenov 2026]

The Timescales of the Interstellar Medium

To explore how gas and star formation are connected across different galactic environments, the authors analyze three simulated systems: a dwarf galaxy, a Milky Way–like galaxy, and a gas-rich starburst galaxy, as shown in Figure 2. Despite spanning very different physical regimes, the galaxies exhibit remarkably similar trends in the fraction of gas actively forming stars as a function of Σ_gas​. This suggests that the amount of star-forming gas is governed primarily by local interstellar conditions, since regions with higher gas surface densities tend to contain denser, more strongly self-gravitating gas.

Figure 2: Using simulations (left to right) of an isolated intermediate-mass dwarf galaxy, Milky Way–like galaxy, and gas-rich galaxy, the authors measure the star-forming gas fraction versus the gas surface density (right). [Adapted from Kocjan and Semenov 2026]

To further understand this trend, this study then applies the authors’ theoretical framework to determine the timescales of ISM gas cycling on the scales of individual star-forming regions. These include the timescales for the formation, dispersal, and local depletion of star-forming gas as described above: τ₊, τ₋, and τ_∗, which also exhibit strong correlations with the gas surface density (see Figure 3). Specifically, the timescale for supplying gas into the star-forming state is linked to the rate at which turbulence redistributes material through the galactic disk. The depletion timescale, over which star-forming gas is turned into stars, decreases at higher Σ_gas​, since denser regions more efficiently collapse and form stars. By contrast, the removal timescale is comparatively short, reflecting how quickly feedback and changes in local equilibrium can disrupt star-forming clouds. In this way, the “boiling kettle” framework is able to capture the major processes driving small-scale gas evolution.

Figure 3: Scaling relations between the supply (left), depletion (middle), and removal (right) times in kiloparsec-scale regions of the simulated galaxies (shown in different colors). Based on the measurements from the simulations, the authors introduce a parameterized model for the gas cycling framework, as defined in the equations. [Adapted from Kocjan and Semenov 2026]

Original astrobite edited by Jayde Willingham.

About the author, Shalini Kurinchi-Vendhan:

After studying astrophysics and literature at Caltech, I moved onto a Fulbright Fellowship in Heidelberg, Germany. I’m passionate about using computer simulations to explore supermassive black holes and galaxy evolution — but I also love poetry and traveling.

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An unusual clump of gas 450 million years after the Big Bang may contain stars hailing from the universe’s elusive first generation of stars. New research examines an alternative explanation involving an accreting black hole.

Meet Hebe

Hebe is visible in the image on the left as a prominent blob of helium emission up and to the left from GN-z11, a luminous galaxy hosting an accreting supermassive black hole. On the right is an infrared image of the same region, in which Hebe is not visible. Click to enlarge. [Adapted from NASA, ESA, CSA, Ralf Crawford (STScI)]

Before the community settles on this exciting explanation, however, the hypothesis must withstand all the tests astronomers can throw at it. In a recent research article, Junehyoung Jeon, Tae Bong Jeong, and Saiyang Zhang (The University of Texas at Austin) along with Volker Bromm (The University of Texas at Austin) attempted to explain Hebe’s properties in another way.

Considering Alternatives

Hebe glows with distinctive helium emission that requires a source of high-energy radiation. This radiation could be provided by a cluster of Pop III stars, but it could also, in theory, arise from an accreting supermassive black hole embedded within the gas clump.

Predicted total mass of Hebe’s Pop III stars as a function of the Lyman–Werner flux from the nearby galaxy GN-z11. Click to enlarge. [Jeon et al. 2026]

Still a Leading Explanation

While the black hole scenario could, with reasonable black hole masses, gas densities, and accretion rates, reproduce individual flux measurements drawn from JWST observations, this hypothesis struggled to simultaneously match multiple measurements. The Pop III star cluster scenario, with a cluster mass of a few hundred thousand solar masses, provided the best fit to the JWST data.

Modeled spectral energy distributions (lines) and predicted line flux densities (open symbols) for the accreting black hole, Pop III star, and Pop II (second-generation) star hypotheses. The observed JWST line fluxes are shown as filled circles. Click to enlarge. [Jeon et al. 2026]

While a cluster of Pop III stars is still the leading explanation for Hebe’s properties, the team noted that the Pop III star and black hole hypotheses aren’t mutually exclusive; Hebe could very well harbor a primordial black hole and a smattering of Pop III stars. Regardless of what powers its characteristic helium emission, Hebe offers an enticing glimpse into the early universe, and more work is needed to understand this intriguing object.

Citation

“What Is Powering the Enigmatic He II Emitter Hebe: The First Stars or Black Holes?” Junehyoung Jeon et al 2026 ApJ 1006 27. doi:10.3847/1538-4357/ae7bea

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What can some neon trapped in a chunk of rock tell us about Earth’s formation and the protosolar nebula? Quite a lot, as detailed in a recent study in The Planetary Science Journal.

Noble Mysteries

By analyzing rocks pulled from mid-ocean ridges, geologists have concluded that there are tiny amounts of noble gases in the deep interior of Earth. That’s a strange statement upon reflection: how did these gases, which are famously apathetic to essentially all other elements, end up embedded within rocks thousands of kilometers underground? Since their passivity rules out the potential of a chemical reaction that formed them in place, they must have been in the mantle since the very beginning of Earth’s history.

A map illustrating the age of the seafloor. Mid-ocean ridges stand out clearly in red. By sampling material from these ridges, planetary scientists can infer the composition of Earth’s deep interior. Click to enlarge. [Mr. Elliot Lim, CIRES and NOAA/NCEI]

That last option is especially exciting to present-day planetary scientists interested in constraining Earth’s formation history because it requires some very specific conditions. Since light noble gases like neon don’t dissolve well in seawater, they must have dissolved into a magma ocean — meaning the nebula was still around when Earth was large enough to have a molten surface. That already restricts us to a very specific time in the solar system’s history, but it doesn’t say much about the specific size of the proto-Earth other than “big,” and it doesn’t say much about the state of the nebula other than “it existed.” Recently, Vincent Savignac and Eve Lee (University of California, San Diego; McGill University) successfully refined these constraints to pin down information about both the early Earth and the nebula that surrounded it.

Infant Earths

Savignac and Lee began by growing a grid of infant Earths on their computers via models of gas accretion and atmosphere–magma interactions. Each simulation started with a different proto-Earth mass and nebular density, and each one yielded a different amount of neon in Earth’s deep interior. Excitingly, only a small handful of the scenarios tested ended up with values similar to those observed.

A schematic of Earth’s formation via embryo formation (when the noble gases enter the mantle) followed by mergers. Click to enlarge. [Savignac & Lee 2026]

Savignac and Lee demonstrated that these constraints are robust against the later stages of Earth’s evolution. In its later years, Earth either suffered or benefited from a giant impact, depending on your feelings about the Moon, but the researchers showed that this event doesn’t pose a problem for their models. Overall, this study builds a delightful link between rocks from our deep oceans and the particulars of Earth’s formation, demonstrating the unique power of planetary science to tie together different scientific fields.

Citation

“Constructing the Earth’s Formation History Using Deep Mantle Noble Gas Reservoirs,” Vincent Savignac and Eve J. Lee 2026 Planet Sci. J. 7 135. doi:10.3847/PSJ/ae64f7

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Researchers have detected molecules containing rings and chains of carbon atoms in the vicinity of a rare pair of quasars. The trends in the distribution of these molecules are unexpected, suggesting that more work is needed to understand the conditions surrounding active supermassive black holes.

Infrared Eyes on Molecules in Space

Examples of aromatic and aliphatic hydrocarbons. Benzene (top left) is the simplest aromatic molecule. Propane (top right) is a simple aliphatic molecule. Propylbenzene (bottom) is an aromatic molecule with an aliphatic chain branching off of it. In these “skeletal” formulae, there is a carbon atom at each vertex, and the remaining atoms (not depicted) are all hydrogens. Single lines indicate single chemical bonds, and double lines indicate double bonds. [Wikipedia; Public Domain]

JWST’s sensitive infrared eyes have allowed researchers to study the distribution, creation, and destruction of both aromatic (containing one or more rings of carbon atoms in which certain electrons spread out within the ring) and aliphatic (containing chains of carbon atoms) hydrocarbons. These molecules have been spotted in a wide array of environments, and now, astronomers are finding them in more distant and more extreme environments than ever before.

Distant Discovery

SDSS J074922.96+225511.7, or J0749+2255 for short, is a quasar pair seen 3 billion years after the Big Bang. The two feasting supermassive black holes are roughly 12,000 light-years apart, giving researchers a glimpse into the late stages of a galaxy merger and a harsh environment in which to study the survival and destruction of molecules.

Researchers studying J0749+2255 with JWST have previously reported the detection of a 3.3-μm emission feature from aromatic molecules. Now, C. E. Mentzer (University of Missouri), Aigen Li (University of Missouri), and Xuejuan Yang (Xiangtan University) have analyzed JWST spectra of J0749+2255 and found not just widespread aromatic emission at a rest-frame wavelength of 3.3 μm, but also aliphatic emission at 3.4 μm, which they attribute to carbon chains branching off from the aromatic molecules. This likely makes J0749+2255 the most distant galaxy in which both aromatic and aliphatic emission has been detected.

Aliphatic fractions in the bright central region surrounding the two quasars (top) and in the outer regions (bottom). [Mentzer et al. 2026]

Unexpected Trends

Mentzer, Li, and Yang subdivided the observations into 47 regions and measured the strength of the 3.3- and 3.4-μm features in each region. This analysis found strong aromatic emission nearest the quasars and showed that the fraction of carbon atoms bound up in aliphatic chains is highest close to the quasars.

Both of these findings are unexpected: the harsh radiation environment near the two active black holes is thought to break apart chains of carbon atoms attached to aromatic rings (which should decrease the 3.4-μm emission) and possibly destroy small aromatic molecules (which should decrease the 3.3-μm emission) — yet both of these features are strongest near the quasar cores where the radiation should be most capable of molecular destruction.

The authors speculated that the analysis regions centered on the quasars are large enough that they contain gas that hasn’t been pummeled by the quasars’ intense radiation and outflows, leaving molecules intact and able to produce the observed emission. However, this doesn’t explain the trend of stronger 3.3- and 3.4-μm emission closer to the quasars — necessitating further research into the emitting behavior of aromatic and aliphatic molecules under the extreme conditions of a dual quasar’s neighborhood.

Citation

“Widespread Detection of Aromatic and Aliphatic Emission in the Dual Quasar J0749+2255 at Cosmic Noon,” C. E. Mentzer et al 2026 ApJL 1005 L38. doi:10.3847/2041-8213/ae7e86

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Mars as an Exoplanet: Lessons from a Planet at the Edge of Habitability
Authors: Stephen R. Kane et al.
First Author’s Institution: University of California, Riverside
Status: Published in PSJ

Mars in the Upside Down

If you’re a fan of Stranger Things like me, you’ll know of the Upside Down: a mirror world similar to our own, but with very different rules. Imagine Mars in the Upside Down, where it is no longer our next-door neighbor but a planet hundreds of light-years away. An astronomer on this Upside Down Earth would be looking at a distant speck with a transit signal barely distinguishable from noise. In this world, Mars would no longer be familiar but completely foreign, with unknown properties. Kane et al. suggest that treating Mars as if it were a stranger is a useful way to think about exoplanet science today.

JWST is hunting for atmospheres on small rocky planets around other stars. However, only a select few Mars-like exoplanets have been discovered (Figure 1). This is because sub-Earth planets are small and hard to detect, testing the bounds of current technology. The ones that have been discovered, such as TRAPPIST-1h and Kepler-138b, were detected due to favorable geometry. They happen to orbit very close to a low-mass star or sit in resonant multi-planet systems, which amplify the signal we are looking for. True Mars analogs with low flux and moderate orbital periods remain out of reach. This is precisely what makes Mars itself so important scientifically — it is the only planet of this type we can study up close.

Figure 1: A plot of confirmed exoplanets by mass and radius. Most confirmed exoplanets are larger and more massive than Earth. Mars-like planets (dots in the blue box) are rare in confirmed exoplanet detections. [Kane et al. 2026]

Getting to Know Mars, Getting to Know All About Mars

We know a lot about Mars in comparison to other planets thanks to rovers (such as Curiosity and Perseverance), atmospheric orbiters (such as Mars Atmosphere and Volatile EvolutioN and the Mars Orbiter Mission), and other science missions (Figure 2). We know it once had water features with neutral pH and favorable chemistry for life from sedimentary evidence at the Gale and Jezero craters. We know its atmosphere is 95% CO₂ with a surface pressure less than 1% of Earth’s. We know it once had an active magnetic dynamo, but the dynamo died out about 4 billion years ago, leading to solar wind steadily stripping away Mars’s atmosphere over time.

Figure 2: Earth and Mars to scale, showing their internal structures and atmospheres. Despite being neighbors, Mars is dramatically smaller with a thin CO₂ atmosphere, similar to the planets JWST is struggling to characterize. [Kane et al. 2026]

Beyond Our Backyard

JWST is currently studying the small rocky TRAPPIST-1 planets and is finding little evidence of atmospheres. The authors of today’s article explore the idea that these exoplanets are similar to Mars and perhaps are undergoing processes that strip away their atmospheres and create optimal conditions for life only for short durations. Using Mars as a blueprint, the authors show how we can better understand exoplanet processes, including volatile delivery and loss, photochemistry, climate evolution, obliquity forcing, planetary architecture, and intrinsic magnetism. For example, measurements of noble gases directly fingerprint Mars’s atmospheric escape process, and the authors argue these give us a calibration framework for interpreting future exoplanet spectra.

The upcoming Nancy Grace Roman Space Telescope’s microlensing survey will start revealing how common true Mars analogs actually are throughout the galaxy, while the future Habitable Worlds Observatory will attempt direct imaging of nearby candidates with unprecedented precision. Together, these missions will tell us whether Mars-like outcomes (brief habitability, catastrophic atmospheric loss, barren surfaces, etc.) are the default fate for small rocky planets. Interpreting that data will require the exact framework this article builds: one grounded in the only Mars analog we can study in detail.

Original astrobite edited by Sandy Chiu.

About the author, Ben Sherwin:

I am a physics PhD student and a National Science Foundation Graduate Research Fellow at Stanford University, working with Josh Frieman. I am interested in theoretical and observational cosmology, specifically in cross-correlations between the cosmic microwave background and tracers of large-scale structure.

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This image, which combines a background view from the Dark Energy Camera Legacy Survey with two inset images from the Very Large Telescope, shows an unusual pair of galaxies in the Fornax Cluster. The galaxies FCC 224 and FCC 240 are under scrutiny because they may have formed via a high-velocity collision between dwarf galaxies — the so-called “bullet-dwarf” model. Using new spectroscopy from the Very Large Telescope, Maria Luísa Buzzo (Yale University) and collaborators analyzed the ages and kinematics of the galaxies’ stars as well as the unusually bright globular clusters swirling around each galaxy. These data suggest that both galaxies are deficient in dark matter, and their stellar populations and globular clusters are all roughly 10 billion years old. The lack of dark matter and the uniform stellar ages are both consistent with the bullet-dwarf model, in which the collision strips away dark matter and ignites a burst of star formation. Since this type of collision can create more than two remnants, the team suggests searching along the trajectory defined by FCC 224 and FCC 240 for more fragments from the collision, some of which may contain the galaxies’ lost dark matter. To learn more about these galaxies and what they might mean for the bullet-dwarf mechanism, be sure to check out the full research article linked below.

Citation

“Dark-Matter-Deficient Twins: FCC 224 and FCC 240 as Possible Analogs of NGC 1052-DF2 and DF4,” Maria Luísa Buzzo et al 2026 ApJ 1005 15. doi:10.3847/1538-4357/ae7349

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The iconic disks of spiral galaxies are well known across the local universe and now far beyond. A recent study looks at the Milky Way to determine when its own disk emerged.

Spinning into Spirals

The Milky Way, a grand spiral galaxy with stars and gas rotating in a disk, did not always look this way. Galaxies begin as chaotic clumps of gas and stars inside a knot of dark matter, and at some point in time, spiral galaxies must transform into the flat rotating disks we observe them as today. Recent JWST observations have uncovered disk galaxies emerging much earlier in the universe than previously thought, shifting our understanding of how quickly spiral galaxies come together and settle into disks. While we cannot study the detailed assembly history of these very distant galaxies, we can dissect galaxies in the local universe to build a better timeline of galaxy evolution.

JWST images of distant edge-on galaxy disks [NASA, ESA, CSA, STScI, Takafumi Tsukui (ANU)]

Stars hold on to the kinematic and chemical information they are born with, so stars of different ages and metallicities across the galaxy should trace the development of the disk. Because stellar ages have been difficult to constrain observationally, studies of galactic spin-up have typically relied on readily available metallicity measurements as a proxy for age; however, metallicity is not a clear-cut age indicator, making it difficult to truly distinguish different stellar populations across the Milky Way’s disk. Luckily, new major surveys have recently provided stellar databases adding the stellar age measurements necessary to pin down when the Milky Way spun up.

Dawn of the Galactic Disk

Plots showing stellar age and rotational velocity (Vϕ) versus metallicity, [Fe/H]. The metallicity range where the age–[Fe/H] relation stalls coincides with the point when the Vϕ–[Fe/H] relation rapidly increases, indicating the age of the spin-up in the Milky Way. Click to enlarge. [Modified from Feltzing et al 2026]

With these star samples, Feltzing and team analyzed how both stellar rotational velocity and age varied with metallicity to determine when the Milky Way spun up. They found that high-α stars clearly move from having random motions to being rotationally supported over a short range of metallicities about 12.5 billion years ago, while the low-α stars seem to begin in a rotating disk and stay there. When varying their selection criteria and looking at the full sample, the authors determined that the Milky Way spin-up happened between 12.1 to 12.5 billion years ago — the first time Milky Way spin-up has been age-dated in this way.

These results imply a rapid chemical evolution and change in kinematic properties as stars went from randomly orbiting to rotating in an ordered disk in the Milky Way. The authors suggest that future studies should focus on lower-metallicity stars to better disentangle stars in the disk from stars in the halo, which will lead to a more precise determination of the Milky Way’s spin-up. Upcoming large-scale surveys will make this possible and allow astronomers to build a better picture of galaxy formation in the early universe.

Citation

“Dawn of the Milky Way Disk: Determination of When a Rotationally Supported Disk Appears and Dating the Spin-up of the Disk,” Sofia Feltzing et al 2026 ApJL 1004 L28. doi:10.3847/2041-8213/ae6f14

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White dwarfs often show signs of metals in their spectra, providing evidence that these evolved stars have accreted planetary material. Could white dwarf spectra also provide evidence for technological activity in these star systems?

A Record of Planets Past

When a Sun-like star reaches the end of its hydrogen-burning lifetime, it first puffs up into a red giant before exposing its white-hot core, which evolves into a white dwarf. This dramatic transition shakes up any planets that happened to be orbiting the star, and some close-in planets may end up crumbling apart, their rubbly remains peppering the surface of the white dwarf.

So far, astronomers have found hundreds of white dwarfs that appear to be polluted with heavy elements from their destroyed planets. These observations provide a valuable look into the bulk compositions of planetary materials outside our solar system. They may also provide a way to detect patterns of chemical abundances that are not natural, resulting from technological processes like industrial refining or the creation of alloys — in other words, a technosignature that is evidence of not just life, but technologically advanced life.

Seeking Signs of Technology

Representation of the chemical abundances of meteorites (pink, orange, and green) and white dwarfs (gray). Most white dwarf abundances overlap with the parameter space defined by the meteorite sample. Click to enlarge. [Huang et al. 2026]

The team used thousands of chemical abundance measurements from meteorites as a reference for the natural bulk composition of planetary material. For the mixture of natural and processed material, they combined the meteorite reference material with a template that is metal-rich and silicate-poor, with enhanced amounts of iron, nickel, chromium, and manganese.

Evidence for a model including technologically processed material relative to a purely natural model, as a function of the number of elements detected in the white dwarf. n_det = 0 indicates that only upper limits were obtained on elemental abundances. Higher Bayes factors indicate stronger evidence. The left-hand plot is based on abundances measured from the white dwarfs’ photospheres, while the right-hand plot uses abundances adjusted for diffusion within the white dwarf. Click to enlarge. [Adapted from Huang et al. 2026]

No Strong Evidence, but a Path Forward

Ultimately, Huang’s team found that strong statistical support for the existence of technological processes was uncommon, though there were certain measurements in their sample of white dwarfs that were difficult to reconcile with a solely natural model.

Perhaps unsurprisingly, the team also found that the quality of the chemical abundance measurements affected the constraining power of the observation; some white dwarfs had upper limits for just a few elements, while others had definitive detections of many elements. They found that the most discerning observations recorded iron, magnesium, chromium, and titanium, plus either nickel, silicon, or sodium.

While this work didn’t dredge up firm evidence for technological activity, it provides a jumping-off point for future searches. The handful of white dwarfs in this sample that were fit poorly by a purely natural model could be compared against other technosignature models or targeted with high-resolution spectroscopy. Future measurements of iron and magnesium in polluted white dwarfs may be useful as a preliminary screening tool, helping to pick out intriguing targets for follow-up observations.

Citation

“A Calibrated Bayesian Search for Potential Chemical Technosignatures in Polluted White Dwarfs,” Bo-Lun Huang et al 2026 ApJ 1006 9. doi:10.3847/1538-4357/ae742c

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Carbon Cycle Imbalances on Arid Terrestrial Planets with Implications for Venus
Authors: Haskelle T. White-Gianella and Joshua Krissansen-Totton
Authors’ Institution: University of Washington
Status: Published in PSJ

The Carbon-Cycle Thermostat

When discussing the habitability of planets, we usually focus on the habitable zone, the region around a star where a planet can host a temperature suitable for supporting liquid water on its surface. Yet, being in the right place doesn’t necessarily guarantee that a planet will be habitable.

A planet also needs the right atmospheric composition to sustain the necessary temperatures for hosting liquid water. A key mechanism found on Earth for maintaining this composition is the geologic carbon cycle, which acts as a built-in climate control system. This cycle begins with volcanic eruptions releasing carbon dioxide (CO₂₎, which then dissolves in rainwater and forms a weak acid that weathers rocks on continents. The weathering products wash into oceans, where they form carbonate rocks, locking carbon away. Eventually, plate tectonics recycles some of that carbon back to volcanoes. The weathering process works faster when the planet is warmer, thus regulating the amount of CO₂ and stabilizing the climate over long periods of time (but it should be noted that it can take up to a few hundred thousand years to rebalance this slow carbon cycle through the weathering process).

An important caveat is that the weathering process requires sufficient liquid water on the planet’s surface, so what happens in the case for planets with shallower oceans? Low-mass M dwarfs, the most common type of star found in the galaxy, are expected to host less-massive disks and therefore lower water inventories for forming planets. If more “dry” planets are indeed a more likely outcome of planet formation, we’d want to know how their arid conditions influence their long-term evolution and habitability.

Creating Carbon-Tracking Models

The authors built a model that tracks how water and CO₂ move between a planet’s interior, oceans, and atmosphere over 4.5 billion years. The model notably includes the following:

• A sophisticated weathering model that accounts for how runoff can limit rock weathering, improving upon previous models that only included a temperature dependence on weathering
• Wind-driven evaporation limits that influence the amount of water evaporation in addition to sunlight-driven evaporation
• Multiple deep water cycle parameterizations that explore how water moves between the interior and the surface

The model tests for four initial surface water inventories (0.1%, 1%, 10%, and 100% of Earth’s oceans) and then simulates how the surface water, atmosphere, and climate evolve over time.

A Critical Water Threshold

The models reveal that planets require at least 20–50% of Earth’s ocean mass to maintain a balanced carbon cycle. Below this threshold, the carbon cycle becomes unbalanced, leading to devastating consequences for habitability (Figure 1).

Figure 1: Final surface temperature after simulating 4.5 billion years of evolution as a function of initial water inventory for Earth-like planets. Each dot represents a model run with different assumptions (total carbon inventory, temperature dependence of weathering, soil age, etc.). The yellow region shows where most simulations result in uninhabitable surface temperatures from an unbalanced carbon cycle, and the cyan region shows where most simulations result in habitable surface temperatures and a balanced carbon cycle. The left and right plots show the results for two different parameterizations of the deep water cycle implemented in the model. [White-Gianella & Krissansen-Totton 2026]

Important Implications (Within and Outside Our Solar System)

Looking within the solar system, the results offer an explanation for how a potentially habitable Venus could have transitioned into its current inhospitable state. If Venus had formed with an initial water inventory below this critical threshold of 20–50% of Earth’s ocean mass, then its carbon cycle would have become unbalanced, creating the CO₂ inferno seen on Venus today.

In future exoplanet studies, telescopes like the Habitable Worlds Observatory might detect ocean glint (specular reflection from liquid water) or measure land fraction from light curves. Finding a planet in the habitable zone but with limited ocean coverage would likely be bad news, as the planet could be quietly losing its grip on habitability. Astronomers may want to be more careful when looking at seemingly promising planets within their habitable zones.

Original astrobite edited by Natalie Price.

About the author, Jared Bull:

I am a 2nd-year PhD student at Johns Hopkins University. I study brown-dwarf variability and am interested in using time-series observations to uncover dynamic processes within their atmospheres. In my free time I like to read, cook, and do astrophotography.

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Many observations of solar flares suffer from saturation and blooming, causing crucial information to be lost. Researchers recently validated a technique for retrieving information from saturated flare images, unlocking a treasure trove of powerful solar flares for examination.

Solutions for Saturation

Since 2010, the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) has been capturing nearly continuous extreme-ultraviolet images of the Sun’s disk, revealing our star’s dramatic high-energy behavior. Though SDO/AIA’s observations have transformed our understanding of the Sun’s activity, they have limitations: powerful solar flares can saturate the detector, spilling charge into nearby pixels.

This saturation and overflow compromises our ability to study the most energetic solar flares — but the “lost” information may actually be recoverable. When light from an intense flare enters SDO’s instruments, not all of it pools in the saturated region of the detector: some of the light is diffracted by the optics, and by mathematically inverting this pattern of diffracted light, researchers can attempt to extract the encoded information about the saturated region. Researchers have used this technique for more than a decade, but options for validating the results were limited until now.

Solar Orbiter Lends a Hand

Launched almost 10 years to the day after SDO, the Solar Orbiter spacecraft provides an excellent opportunity to test inversion techniques for recovering information from saturated solar images. Solar Orbiter’s Extreme Ultraviolet Imager snaps brief photos of the Sun at a rapid cadence, and its images remain unsaturated even when faced with energetic solar flares.

Positions of SDO (green) and Solar Orbiter (blue) during a solar flare on 19 March 2024. Click to enlarge. [Guastavino et al. 2026]

Guastavino’s team aligned and reprojected the data, accounting for the slightly different viewing angles of the two spacecraft, then applied an algorithm called Adaptive SE-DESAT to reconstruct the flux within the saturated portion of the SDO image. The team compared the desaturated SDO images to the unsaturated Solar Orbiter images over the course of the flare, finding the same flare morphology and similar time evolution between the two data sets.

Example of unprocessed SDO data (top left), desaturated SDO data (top right), Solar Orbiter data (bottom left), and a combination of the two data sources (bottom right). Note that the Solar Orbiter observations have been clipped so that only the highest flare intensities were recorded. Click to enlarge. [Adapted from Guastavino et al. 2026]

A Treasure Trove of Desaturated Data

Overall, these results demonstrate the effectiveness of the inversion technique, though Guastavino and coauthors noted that improvements could be made during the impulsive phase of the flare, when the emission is increasing. The team identified several reasons why the results may not match during this phase, including rapid evolution of the flare during individual exposures.

Despite these areas that require further attention, the validation of this technique unlocks 16 years of solar flare observations from SDO. This especially enhances our sample of powerful solar flares, increasing the available records of the most energetic solar flares by orders of magnitude.

Citation

“Validation of an Extreme-Ultraviolet Desaturation Technique for the Atmospheric Imaging Assembly on Board the Solar Dynamics Observatory Using Observations from the Extreme Ultraviolet Imager on Board Solar Orbiter,” Sabrina Guastavino et al 2026 ApJL 1005 L50. doi:10.3847/2041-8213/ae7d2e

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NASA is once again sending scientific missions to the Moon. But under the new commercial framework for getting there, researchers need to invent a new method for how to pick where to land.

A New Process for Picking Sites

NASA’s Commercial Lunar Payload Services program is a bold innovation in organizing robotic missions to the Moon. Under this model, rather than keeping the mission process entirely in-house, the agency selects the scientific mission they want to support then simply buys a ride to the lunar surface from a commercial vendor. But, how do you pick a landing site before you know exactly how you’re getting there?

The Gruithuisen domes region, the broad area the Lunar-VISE team searched for potential landing sites. Click to enlarge. [Adapted from Williams et al. 2026]

No Parking Lots on the Moon

Picking a landing site is no small task: for context, selecting the landing sites for each of the most recent Mars rovers took five years and multiple community workshops. The Lunar-VISE team therefore took a streamlined and logic-driven approach. They started by explicitly laying out their science objectives: Lunar-VISE’s purpose is to investigate some strangely silicate-rich volcanic formations called the Gruithuisen domes, so they had to land either on or near those. They also had to have access to boulders that were excavated from deep within the domes during a crater formation event, so they had to pick a spot with boulders relatively nearby.

In addition to objectives, they also laid out a slew of constraints. Although they needed boulders nearby, they couldn’t have too many boulders, or any particularly large boulders, since those could pose hazards for landing. There also couldn’t be any steep slopes in the field. Most of the area had to maintain a line of sight with a supporting orbiter for communications, so they couldn’t set down near any ridges. Also, they had to consider how the terrain would cast shadows as the lunar day progressed, since they didn’t want their mission cut short by freezing temperatures and a lack of solar power. As the team quipped, “many interesting, high-science value locations on the Moon may not be in proverbial ‘parking lots.'”

An image from the Lunar Reconnaissance Orbiter overlaid onto a terrain model of the final landing site. Click to enlarge. [Williams et al. 2026]

In addition to presenting their landing site, the researchers offered a handful of lessons to others who may someday be in the fortunate and thrilling position of needing to pick a landing spot on the Moon. For one, they urged teams to coordinate with the Lunar Reconnaissance Orbiter specialists as early as possible, since processing the imaging data for lander-quality maps is a specialized and intensive task. For another, they recommended that all of the software tools used be made publicly available so that future missions don’t need to duplicate their work.

As this article laid out, the Commercial Lunar Payload Services program and Lunar-VISE take us one step closer to making missions to the Moon routine — but we’re still figuring out exactly how to do that.

Citation

“Lunar-VISE Landing Site Selection and Characterization at Mons Gruithuisen Gamma,” Jean-Pierre Williams et al 2026 Planet. Sci. J. 7 161. doi:10.3847/PSJ/ae7d2c

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Do all star-forming regions birth stars with the same distribution of masses? Theory suggests that they do not, but researchers often assume they do for simplicity. Now, ultra-precise observations from Gaia have demonstrated that the initial mass function varies across star clusters in the Milky Way.

A Universal Initial Mass Function?

The light from distant galaxies is dominated by high-mass stars, requiring the use of the IMF to estimate the stellar mass of a galaxy. [ESA/Webb, NASA & CSA, G. Östlin, P. G. Perez-Gonzalez, J. Melinder, the JADES Collaboration, the MIDIS collaboration, M. Zamani (ESA/Webb); CC BY 4.0]

The IMF is important in many areas of astronomy, and it’s relied on especially heavily in studies of distant galaxies. The light from these galaxies is dominated by high-mass stars, with the emission from lower-mass stars lost in the glare, so astronomers must use the IMF to reconstruct the stellar populations of these far-off locales.

Though theory suggests that the IMF should vary with factors like temperature and metallicity, demonstrating these variations has been difficult, even within our own galaxy. Because of this, researchers often adopt a universal IMF drawn from observations of star clusters in the Milky Way. But is the IMF truly universal?

The More the Slope Changes, the More the Break Mass Stays the Same

Determining whether the IMF is universal is more complicated than simply comparing the stars in one cluster to those in another. That’s because what astronomers measure in present-day star clusters is not the initial mass function, but a version of the IMF that has been skewed by millions to billions of years of evolution; over time, high-mass stars die and low-mass stars get ejected, warping the shape of the mass function.

Left: Different break masses arise for different properties (here, the sound speed) of a given star-forming cloud. Right: Evolution of the mass function over time for a single star cluster. Over time, high-mass stars die and low-mass stars are ejected from the cluster, resulting in a decrease in the remaining mass fraction, μ, from 1 to 0.1. The slopes change, but the break mass does not. Click to enlarge. [Adapted from Steinhardt et al. 2026]

Insights from Gaia

Thanks to the Gaia spacecraft, which made precise observations of more than 2 billion stars in the Milky Way and beyond, it’s now possible to measure and compare the break masses of individual star clusters. Out of an initial catalog of 7,167 Milky Way clusters observed with Gaia, Steinhardt’s team selected just 110 that were of high enough quality and contained a sufficient number of stars to measure cluster break masses accurately.

Observed mass functions of four Milky Way star clusters. The break masses are clearly different, showing that the IMF must vary from cluster to cluster. Click to enlarge. [Steinhardt et al. 2026]

This finding has implications for studies of high-redshift galaxies, where the properties of star-forming clouds are markedly different from those in the Milky Way. Going forward, Steinhardt and coauthors recommend developing a flexible parameterization of the IMF to capture how this critical function behaves in environments vastly different from our own.

Citation

“Direct Evidence for Stellar Initial Mass Function Variation in the Milky Way,” Charles L. Steinhardt et al 2026 ApJL 1005 L40. doi:10.3847/2041-8213/ae7444

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: MAGAZ3NE: Confirming Dust Deficiency and Quiescent Nature of Ultramassive Galaxies at 3 < z < 4 with ALMA Observations
Authors: Wenjun Chang et al.
First Author’s Institution: University of California, Riverside
Status: Published in ApJ

Distant galaxies offer a unique window into how stars, gas, and dust evolve over cosmic time. Tracing this evolution requires understanding not only how galaxies form, but also how and when they stop forming stars, a process known as quenching. Understanding how, when, and why galaxies quench is a fundamental question in astrophysics, and one that requires observations of star-forming, quenching, and fully quenched galaxies alike. Unfortunately, one complication is that identifying truly quenched galaxies is challenging: galaxies that appear “dead” may instead be actively forming stars, hidden behind a thick veil of dust.

In today’s article, the authors use observations from the Atacama Large Millimetre/submillimetre Array (ALMA) to investigate five ultramassive galaxies at redshifts, z, between 3 and 4, and ask a deceptively simple question: are these massive red galaxies genuinely quenched, or are they secretly forming stars behind the scenes?

Meet the Suspects: Ultramassive Galaxies at the Edge of Cosmic Noon

The five galaxies in this study are drawn from the Massive Ancient Galaxies at z > 3 NEar-infrared (MAGAZ3NE) survey, which targets some of the most massive galaxies known at early cosmic times. All five have stellar masses exceeding 100 billion solar masses and have been confirmed at z > 3. At these redshifts, we are observing the galaxies as they were when the universe was less than 2 billion years old. This is just before an epoch known as cosmic noon, when star formation across the universe reached its peak.

These galaxies also benefit from extensive multiwavelength observations from a range of observatories, including the ground-based Visible and Infrared Survey Telescope for Astronomy and the Spitzer Space Telescope. By combining imaging across wavelengths from the ultraviolet to the near-infrared, astronomers can measure the “colours” of galaxies and use these colours to infer the galaxies’ star-forming activity.

Galaxies that have quenched their star formation are dominated by older stellar populations, which makes them appear red (hence why they are often referred to as “red and dead” galaxies). However, dust can redden galaxies in a similar way by absorbing blue light and re-emitting it at longer wavelengths — meaning that a dusty, star-forming galaxy can easily masquerade as a quenched one. To uncover any hidden star formation, the authors turn to ALMA to search for far-infrared dust emission. The sample of galaxies investigated with ALMA is shown in Figure 1.

Figure 1: UVJ colour–colour diagram, which uses galaxy colours in the ultraviolet (U), visible (V), and near-infrared (J) to identify quenched galaxies. The five ultramassive galaxies (UMGs) studied here (filled cyan circles) lie firmly in the quenched region (QG), consistent with a lack of ongoing star formation. Crosses indicate galaxies undetected in ALMA dust emission, while other massive galaxies at similar redshifts are shown in grey for comparison. [Chang et al. 2026]

ALMA on the Scene

ALMA observes light at sub-millimetre wavelengths, which at these redshifts traces emission from star-forming regions that are obscured by dust. Of the five ultramassive galaxies in this sample, only one is detected with ALMA. Even when the remaining four galaxies are stacked together, no dust emission is recovered, indicating that if any dust is present, it must be extremely faint.

To better quantify what these ALMA non-detections imply, the authors perform spectral energy distribution fitting (see a recent overview bite on spectral energy distribution fitting) using the Code Investigating GALaxy Emission, or CIGALE, a code that enforces energy balance between absorbed starlight and dust emission to estimate physical properties such as a galaxy’s star formation rate and dust content. With the ALMA constraints included, all five galaxies are found to lie more than 10 times below the star-forming main sequence. Even the single ALMA-detected galaxy remains formally quenched, showing only weak residual star formation.

In other words, these galaxies really are dead (or at least extremely dormant).

Extremely Dust-Poor Galaxies

The spectral energy distribution fitting also allows the authors to measure how much dust these galaxies contain relative to their stellar mass. This ratio provides a simple but powerful way to assess how much interstellar material remains in a galaxy — and therefore how much fuel is left for future star formation.

Three of the five ultramassive galaxies have ratios of M_dust/M_star < 10^-4 (Figure 2), placing them among the most dust-poor quenched galaxies confirmed at z > 3. The lone galaxy detected by ALMA contains slightly more dust, with M_dust/M_star = 10^-3, but even this is far below what would be expected for an actively star-forming galaxy. For comparison, typical star-forming galaxies at similar stellar masses host more than 100 times more dust.

Figure 2: The ratio of dust mass to stellar mass versus redshift for massive quenched galaxies (QGs). This quantity measures how dust rich a galaxy is compared to its stellar mass. The ultramassive galaxies in this study (cyan pentagons) fall well below the dust content expected for star-forming galaxies (solid blue line), highlighting their extreme dust deficiency. [Adapted from Chang et al. 2026]

For now, ALMA has delivered a clear answer to the question of “dead or in disguise?”: at least some candidate ultramassive galaxies in the early universe really are quenched, and they are strikingly dust poor. By ruling out the dusty impostor scenario, this study shows that deep ALMA observations can cleanly distinguish genuinely quenched galaxies from dusty star-forming ones, even at the highest stellar masses and earliest cosmic times. How these galaxies lost their dust remains an open question, but one thing is clear: by the time cosmic noon arrived, some galaxies had already finished forming stars and quietly faded into dormancy.

Original astrobite edited by Viviana Cáceres.

About the author, Lucie Rowland:

I’m a fourth (and final!) year PhD student at Leiden Observatory in the Netherlands, studying massive, star forming galaxies in the early universe with ALMA and JWST. It’s a really exciting time to be interested in astronomy, so I hope to make groundbreaking new research more accessible!

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The Bullet Cluster is best known for being considered a “smoking gun” for the existence of dark matter, but even a famous galaxy cluster like this one has its secrets. For more than two decades, different measurements of the merging clusters’ dynamical mass ratio have yielded vastly different results. In a recent research article, Boseong Young Cho (Yonsei University) and collaborators used data from JWST and the Dark Energy Camera to revisit the Bullet Cluster and measure its mass ratio using new data. The image above shows a near-infrared view of the Bullet Cluster from JWST, with an overlay of mass contours derived from gravitational-lensing measurements. The team’s analysis assigned a mass of 1.5 quadrillion solar masses for the main cluster (on the left side of the image above), and a mass of 150 trillion solar masses for the subcluster. This suggests a mass ratio of roughly 10, which matches the value supported by hydrodynamical simulations and cements the event as a minor merger. The team also identified three distinct cluster halos (two in the main cluster and one in the subcluster), providing an important constraint on the cluster configuration for future modeling. To learn more about this investigation of the Bullet Cluster, be sure to check out the full research article linked below!

Citation

“Joint JWST–DECam Lensing Reveals that the Bullet Cluster Is a Minor Merger,” Boseong Young Cho et al 2026 ApJ 1005 28. doi:10.3847/1538-4357/ae6a90

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Stellar rotation is a crucial aspect of not only stellar evolution but also exoplanet science, and a recent study has built the largest catalog of stellar rotation periods to date.

Stellar Opportunities with TESS

Since its launch in 2018, the Transiting Exoplanet Survey Satellite (TESS) has scoured the sky, searching for the signature recurring dip in starlight caused by planetary companions. While the primary goal of TESS is to discover exoplanets, the satellite’s mapping of the entire sky has created a rich database of high-quality photometry for millions of stars. These observations offer ample opportunity for scientists to study stellar properties and behavior across the Milky Way.

In particular, stellar rotation is a key property that traces a star’s age, magnetic activity, and internal structure. For exoplanet science, stellar rotation is both a help and a hindrance: it allows us to study how exoplanets may evolve over time with their host stars, but stellar activity can mimic or drown out planet signals, making them harder to detect. A few studies have investigated stellar rotation periods with TESS, looking at specific star clusters and known planet hosts. To date, however, no existing study has produced a larger catalog of TESS rotation periods — a product that would provide a wealth of information for both exoplanet and stellar evolution science.

Creating a Catalog

Target sample summary showing the TESS sky coverage (top left), histogram of number of TESS observations per star (top right), TESS magnitude as a function of distance to the star (bottom left), and histograms of magnitude, distance, temperature, and color across the sample (bottom right). Click to enlarge. [Boyle et al 2026]

Not all brightness variations present in a star’s light curve are due to stellar variability — instrumental systematics and artifacts from the spacecraft’s orbital period can produce periodic variability. To combat this, the authors created a classification algorithm to select sources whose periodicity is most likely due to true stellar variability rather than instrumental or observational effects. Pairing this classification with some additional validation criteria, the authors built the TESS All-Sky Rotation Survey (TARS), a catalog of periods for 1,046,317 stars within about 1,600 light-years of our Sun.

Map of all TARS stars within about 1,600 light-years of the Sun (left) and only the fast-rotating stars in the survey, highlighting clustered populations (right). Click to enlarge. [Boyle et al 2026]

Implications of TARS

Looking more finely at the TARS catalog, the authors provided additional quality cuts to remove other potential sources of stellar variability like binary companions or pulsations. The authors estimated that roughly 93% of their measured periods are due to stellar rotation, which expands the number of stars with known rotation periods by a factor of 2.3 within about 325 light-years and by a factor of 4.0 within about 1,600 light-years. As the largest homogeneous catalog of stellar rotation periods to date, TARS lays the groundwork for studies of stellar evolution, exoplanet discovery and evolution, and even Milky Way structure. For example, the authors found that when mapping the fast-rotating, typically younger stars in TARS, the location of young stellar associations in the local neighborhood became significantly clearer. This underscores the importance of this catalog for a range of science goals, and future work will only improve upon the data provided by TARS.

Citation

“The TESS All-Sky Rotation Survey: Periods for 1,046,317 Stars within 500 pc,” Andrew W. Boyle et al 2026 ApJS 284 75. doi:10.3847/1538-4365/ae6657

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One of the biggest discoveries from JWST’s tenure is a population of compact reddish objects nicknamed “little red dots.” Numerous theories have been proposed to explain the small sizes, high luminosities, and characteristic “V”-shaped spectra of these objects, and today we’ll examine two recent research articles that have explored the identity of the universe’s most mysterious inhabitants.

Red Dot, Blue Dot

You can tell a lot about a person by looking at their friends — and the same might be true for little red dots. A team led by Josephine Baggen (Yale University) examined a sample of 83 little red dots imaged with JWST. They found that 43% of the little red dots in this sample had a little blue companion: an ultraviolet-bright object within a projected separation of 1,630–16,300 light-years. The brightest little red dots were even more likely to have a blue companion; 80% of the brightest objects in the sample were paired up.

Baggen’s team set out to test the hypothesis that these red–blue pairs are fundamentally linked rather than coincidental. Under this hypothesis, the ultraviolet-bright blue companions were assembled first. The ultraviolet radiation from these objects suppressed the cooling of molecular hydrogen in pristine gas clouds in the early universe, causing the gas to skip the usual star-forming process and instead form a massive compact object such as a black hole star, supermassive star, or quasi-star — which we see as a little red dot.

The companion’s mean flux density from 91.2 to 111 nm versus projected separation between the blue companion and the little red dot. The red dashed line shows the estimated values necessary for gas clouds to collapse. Click to enlarge. [Baggen et al. 2026]

If little red dots form thanks to their little blue companions, that would imply that every little red dot has or had such a companion. Though little blue companions weren’t so universal in the sample used in this work, the team noted that their analysis techniques, combined with observational limitations and other factors, likely yielded a smaller number of blue companions than are actually present. Further simulations exploring the collapse of pristine gas clouds into massive compact objects and high-resolution spectroscopic observations of little red dots can illuminate the potential link between these objects.

The densely packed globular cluster NGC 1851, as seen by the Hubble Space Telescope. [NASA, ESA, and G. Piotto (Università degli Studi di Padova); Processing: Gladys Kober (NASA/Catholic University of America)]

Little Red Dots as Young Globular Clusters

John Chisholm (The University of Texas at Austin) and collaborators hypothesized that little red dots represent a brief phase in the formation of globular clusters. In this hypothesis, the rest-frame ultraviolet emission of little red dots comes from the hot young stars of the newborn cluster, while the rest-frame optical emission comes from a single supermassive star at the cluster’s heart. Thus, in this framework, the little red dot phase lasts only as long as the fleeting lifespan of the supermassive star.

Chisholm’s team first showed that the spectrum of a young globular cluster with a supermassive star at its center is similar to the observed spectrum of a little red dot. But showing that the emission properties of globular clusters in formation and little red dots are similar is not enough — it’s also necessary to investigate whether the numbers and masses of these objects line up.

Comparison of the mass functions of little red dots evolved forward to the present day (blue line) and globular clusters in the Milky Way and Virgo (blue symbols). The results for both populations have been normalized to emphasize the shape of the distributions. Click to enlarge. [Chisholm et al. 2026]

In addition to describing how the properties of globular clusters in formation match those of little red dots, Chisholm’s team outlined some testable predictions for this scenario, including formation timescales and chemical abundance patterns. If this hypothesis withstands further scrutiny, little red dots may provide a valuable look at the early years of some of our universe’s oldest star clusters.

Citation

“Connecting the Dots: UV-Bright Companions of Little Red Dots as Lyman–Werner Sources Enabling Direct-Collapse Black Hole Formation,” Josephine F. W. Baggen et al 2026 ApJL 1002 L4. doi:10.3847/2041-8213/ae58a5

“Little Red Dots as Globular Clusters in Formation,” John Chisholm et al 2026 ApJL 1004 L4. doi:10.3847/2041-8213/ae6dae

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: The Wandering Supermassive Black Hole Powering the Off-Nuclear Tidal Disruption Event AT2024tvd
Authors: M. Guolo et al.
First Author’s Institution: Johns Hopkins University
Status: Published in ApJL

A Star Gets Eaten in the Wrong Neighborhood

We find supermassive black holes at the centers of most large galaxies. They end up there because of how galaxies form: as matter collapses and merges over time, material sinks to the gravitational center, and the black hole settles in.

So, what happens when we catch a star being ripped apart by a supermassive black hole that is not at the center of its galaxy?

That is exactly the puzzle posed by AT2024tvd, a tidal disruption event (TDE) spotted roughly 2,600 light-years from the center of a massive galaxy located 600 million light-years away from us (see Figure 1).

Figure 1: A color image of AT2024tvd from the Hubble Space Telescope and JWST. The yellow dot inside the square marks the galaxy’s center, while the TDE is the white dot, which is visibly offset to the upper left, about 2,600 light-years away. [Adapted from Guolo et al. 2026]

Measuring Mass Using Light

To figure out the mass of the black hole responsible for AT2024tvd, the authors needed to get creative. You cannot weigh a black hole directly, so astronomers have to work backward from what they can see. The key idea is that a black hole’s mass controls how its accretion disk behaves. A more massive black hole produces a larger, cooler disk, while a less massive one produces a smaller, hotter disk. By measuring how bright the disk is at different wavelengths and how hot it gets, you can figure out how massive the black hole must be.

The authors did this by modeling the light the event produced across many wavelengths. They combined data from several telescopes: the Zwicky Transient Facility, the Neil Gehrels Swift Observatory, Pan-STARRS, and two rounds of high-quality X-ray data from XMM-Newton. TDE light curves go through different phases. The early flare in visible and ultraviolet light is bright but complicated, and the physical processes behind it are not fully understood. But after a few hundred days, TDEs settle into a quieter “plateau phase,” where the ultraviolet and visible light come directly from the accretion disk. At this stage, the emission follows well-understood physics, and astronomers can model it reliably.

The authors used a model called kerrSED, which describes the spectral energy distribution (SED) of a spinning black hole’s accretion disk (kerr). It accounts for the disk’s temperature, its physical size, the black hole’s spin (how fast it rotates), and the angle at which we are viewing the system. It also accounts for a process called Comptonization, where hot electrons near the black hole boost lower-energy photons (particles of light) up to X-ray energies. By fitting this model to the observed light at multiple wavelengths simultaneously, the authors could pin down the disk properties and extract the black hole mass. The result was a clean fit: the disk model alone could explain all the observed light during the plateau phase, with nothing significant left over (see Figure 2).

Figure 2: The brightness of AT2024tvd measured across a wide range of wavelengths, after correcting for absorption and the galaxy’s motion. The symbols show individual measurements from different telescopes, while the shaded contours represent the best-fit disk model and its uncertainty. Left: The early X-ray data, which is well explained by emission from the hot inner accretion disk. Right: The later data covering both visible/ultraviolet light and X-rays, all consistently explained by the same disk model. [Adapted from Guolo et al. 2026]

Not an Intermediate, but a Supermassive Black Hole

From their fit, the authors found a black hole mass of about one million solar masses. Black holes above about 100,000 solar masses are considered supermassive, while those below that threshold but above about 100 solar masses are called intermediate-mass black holes. So, this puts AT2024tvd in the supermassive category. This matters because the two previously known off-nuclear TDEs, called 3XMM J2150-05 and EP240222a, were both powered by intermediate-mass black holes. Those black holes were found inside small, dense collections of stars called ultra-compact dwarf galaxies that were orbiting larger host galaxies.

AT2024tvd is different. When the authors looked at deep images of the location where the TDE happened, they found no star cluster or small galaxy there. Whatever group of stars once surrounded this black hole has been almost entirely pulled apart by the gravity of the much larger parent galaxy. The ratio of the black hole’s mass to the mass of any remaining stars around it is extreme: greater than 3%, which is far above what we normally see. This is the signature of a “wandering” supermassive black hole, one that was brought in during a past galaxy merger and has been slowly sinking toward the center of its new host ever since, losing its surrounding stars along the way.

The authors compared AT2024tvd to other TDEs using established relationships between accretion disk properties and black hole mass (Figure 3). In terms of its disk temperature, luminosity, and inferred mass, AT2024tvd behaves like a typical nuclear TDE powered by a supermassive black hole. However, when placed on the black hole mass versus host stellar mass relation, it stands out as a strong outlier. The black hole mass is far too large for the small amount of surrounding stellar mass detected at its location.

Figure 3: AT2024tvd (yellow star) plotted on the relationship between black hole mass and host galaxy stellar mass. Red squares show nearby galaxies with dynamically measured black hole masses plotted against galaxy bulge stellar mass, while blue squares show the relation using total galaxy stellar mass. Purple points and green diamonds represent nuclear TDE host galaxies with black hole masses inferred from different TDE modeling techniques. Yellow diamonds mark the two previously known off-nuclear TDEs. AT2024tvd stands out as a clear outlier, with a very high black hole mass compared to the upper limit on any surrounding stellar mass. [Guolo et al. 2026]

The Big Picture

This discovery matters for several reasons. It shows that off-nuclear TDEs are not limited to intermediate-mass black holes sitting in small satellite galaxies. Some are powered by fully supermassive black holes that have been displaced from their original galactic centers. It also shows that TDE modeling, when done carefully during the plateau phase of the light curve (when the emission is dominated by well-understood accretion disk physics), can provide reliable black hole masses on its own, without assuming any relationship between the black hole and its host galaxy. This is particularly important for wandering black holes, where those relationships do not apply.

Looking ahead, upcoming surveys like Vera C. Rubin Observatory’s Legacy Survey of Space and Time are expected to find many more off-nuclear TDEs. Combined with X-ray follow-up from telescopes like XMM-Newton, these events could become our main tool for mapping out the population of displaced black holes in the nearby universe. One disrupted star at a time, we are starting to find black holes that theory told us should exist but that had, until now, stayed hidden.

Original astrobite edited by Kelsie Taylor and Veronika Dornan.

About the author, Serat Saad:

Serat is a first-year PhD student in astronomy at The Ohio State University. His research is on stellar and galactic dynamics, where he uses observational data to understand gravity. He also has interests in active galactic nuclei and tidal disruption events.

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Microlensing surveys have discovered plenty of regular exoplanets, but more surprisingly, they’ve also turned up many solo Neptunes with no star nearby. New research suggests that first impressions might be deceiving, however, and that at least some of these planets might not be so alone: they just have a complicated family history.

An Abundance of Exo-Neptunes

There are simply too many Neptune-like exoplanets in our galaxy. Or at least that’s the current feeling astronomers get from gravitational microlensing surveys, which look for exoplanets during short-lived magnification events caused by chance alignments between stars. These surveys have now found about a dozen so-called “free-floating” planets, and while this doesn’t sound like that many, running the numbers reveals that this tiny sample implies that there are about two free-floating Neptune-size planets for every star in the galaxy.

An illustration of how exoplanets are found via microlensing. The broad first bump is caused by the host star magnifying the light from a background star; the narrow second bump is caused by the planet acting as a lens as well. “Free-floating” planets create only one bump. [Adapted from NASA, ESA, and A. Feild (STScI)]

However, new research by Sam Hadden (Canadian Institute for Theoretical Astrophysics) and Yanqin Wu (University of Toronto) presents an alternative idea: what if at least some of these free-floating planets aren’t fully on their own, but instead remain estranged but weakly bound to their parent stars?

Simulated Scattering

Two celestial objects need to align nearly perfectly in order to create a microlensing pulse that we can detect. For an exoplanet orbiting a star, we should observe two of these pulses: one when the host star drifts in and out of alignment with a background star, and one when the nearby bound planet does the same. In the case of a free-floating planet, there’s only one pulse, and we therefore assume that there is no host star. Hadden and Wu noticed that since the alignment has to be so precise for microlensing to occur, it’s possible that a seemingly free-floating planet is simply widely separated from its host star, and the star managed to dodge the magnification effect. In other words, these planets might not be free floating at all, just on wide and eccentric orbits.

The orbital evolution of a five-planet system that undergoes planet–planet scattering. Each line represents one planet; note that in the end two are ejected, two end up on wide detached orbits, and the fifth ends up on a tightly bound inner orbit. Click to enlarge. [Hadden & Yu 2026]

They found that both types of simulations readily created the “detached” objects needed to mimic free-floating planets. In fact, the most common outcome was for two or three planets to be bullied into far-out orbits by a planet that then plunges onto a tight inner orbit extremely close to the star.

Though the authors caution that this process likely doesn’t explain all of the free-floating planets observed to date, this is an exciting model that would dramatically lower our estimates of the number of Neptunes roaming alone between the stars.

Citation

“Free Floating or Merely Detached?,” Sam Hadden and Yanqin Wu 2026 ApJ 1000 70. doi:10.3847/1538-4357/ae6508

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Fullerenes — a class of molecules composed entirely of interconnected carbon atoms — are the largest molecules definitively detected in space. Researchers using JWST to study a planetary nebula have found new spectral features from a fullerene composed of 60 carbon atoms, offering another way to study how these molecules form and survive in space.

Full of Fullerenes

Planetary nebula Tc 1 as seen by JWST. [NASA / ESA / CSA / Western University, J. Cami]

Since that discovery, Tc 1 has been a hot spot for studies of buckyballs. However, researchers are still puzzling over how these large molecules form and survive in harsh space environments.

A closeup of the center of Tc 1, showing the region observed with JWST’s Mid-Infrared Instrument (black-to-yellow color scale) and Near-Infrared Spectrograph (white outline). The background color scale shows the nebula’s H-alpha emission as seen by the Very Large Telescope. [Adapted from Giese et al. 2026]

From Spitzer to JWST

Morgan Giese (The University of Western Ontario) and collaborators recently reported on the results of a JWST observing program that aimed to understand how fullerenes respond to changes in their environment. The team mapped the distribution of C₆₀ molecules at varying distances from the powerful ionizing radiation of Tc 1’s central star.

The team successfully spotted the emission features from the fullerene C₆₀ seen in earlier observations, but they also turned up something unexpected: a handful of prominent emission features from 3.5 to 5.2 microns that had not been reported previously.

Feature Presentation

What’s the source of these emission features? The distribution of the emission provides a strong clue: known spectral features from fullerenes C₆₀ and C₇₀ are concentrated in a narrow, bright ring around the center of the nebula, with diffuse emission suffusing the rest of the nebula — and the newfound spectral features follow the same distribution.

JWST spectrum of Tc 1 (black line) extracted from the area indicated by a black circle in the previous image. The orange and blue dashed lines show fits to the newfound emission bands, and the results of the anharmonic calculations are shown as the teal line below the JWST spectrum. Click to enlarge. [Giese et al. 2026]

Giese and coauthors found that 17% of the energy emitted by the C₆₀ molecules in Tc 1 is released in these  combination bands, suggesting that these features must be taken into account when modeling the cooling of C₆₀ molecules. The discovery of new fullerene spectral features also has implications for future studies of these molecules: since these features appear in a wavelength range where features from other complex molecules like polycyclic aromatic hydrocarbons are weak, these newly identified bands provide a promising way to spot and study fullerenes across space environments.

Citation

“Detection of C₆₀ Combination Bands in the Near-IR Spectrum of Tc 1,” Morgan M. Giese et al 2026 ApJL 1004 L32. doi:10.3847/2041-8213/ae76d5

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: A GLIMPSE of Intermediate Mass Black Holes in the Epoch of Reionization: Witnessing the Descendants of Direct Collapse?
Authors: Qinyue Fei et al.
First Author’s Institution: University of Toronto
Status: Published in ApJ

In the late 2010s, astronomers were getting hints of something strange going on in the early universe. Using the most powerful telescopes on the ground, we were able to find black holes in the centers of some of the most distant galaxies. The light from these active galactic nuclei (AGNs) was emitted over 12 billion years ago, revealing conditions close to the beginning of cosmic time.

To an astronomer, that’s the mundane part. I’m only half joking — thousands of AGNs had already been identified in the previous half century. However, the most distant of these sources were startling because their central black holes appeared much more massive than expected. To be specific, we know how much mass black holes can start with, and we can write down equations to predict how quickly they should grow. The AGNs we observed seemed to violate these predictions. This raised some serious questions and was highlighted as a major point of inquiry to focus on going into the 2020s.

Then JWST launched, and the mystery grew deeper. No matter where we looked, enormous black holes kept cropping up in astonishing numbers. Astronomers who model the universe with equations and computer simulations have tried to explain these results, but this has been a serious challenge. Some researchers have broken the emergency glass and reached for a highly theoretical tool: the direct-collapse black hole. Unlike the normal pathway for forming black holes (the deaths of massive stars), this model suggests that an enormous cloud of gas could directly collapse into a black hole without forming a star at all. The resulting black holes could have as much mass as a hundred thousand Suns put together — orders of magnitude more than a “normal” black hole. Although this pathway can explain the presence of huge black holes so early in the universe’s history, we’ve never directly seen this happen, so for now it remains just a theoretical possibility.

However, if direct-collapse black holes were widespread at early times, there is one indirect signature we might be able to detect: a large population of intermediate-mass black holes with masses between a hundred thousand and a million times that of the Sun. If we can find such a population, we’ll have strong evidence for the direct-collapse model. Let’s go looking!

Intermediate Mass, Impossible Difficulty

Identifying intermediate-mass black holes requires a tricky combination of spectral resolution and sensitivity. Light from an object must be examined very finely in order to detect the telltale features of an intermediate-mass black hole. However, these sources are already quite faint, so spreading their emission this thin means that any potential signal is very likely to get lost in the noise.

The authors of today’s article use an unprecedented set of observations to leap over this hurdle and directly probe intermediate-mass black holes. They not only use the most sensitive spectroscopic instrument (NIRSpec) on the most powerful space telescope (JWST), but they take advantage of a phenomenon known as gravitational lensing.

According to Einstein’s general theory of relativity, gravity is the result of matter curving spacetime. Areas with more concentrated matter will experience stronger curvature. When an object traveling in a completely straight line moves through curved space, its path appears bent. This same effect happens to light. Intriguingly, a large concentration of matter can redirect diverging rays of light to a focus, acting like an enormous magnifying glass.

Astronomers take advantage of gravitational lensing by pointing telescopes at massive clusters of galaxies. The intense gravity of these regions can magnify sources in the background by tens or even hundreds of times. Galaxies that would be impossibly faint to see under normal conditions can thus be observed if they are strongly lensed, making this a powerful technique to examine otherwise hidden objects.

Putting Faint AGNs Under a Lens

The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) program took extremely powerful observations of a galaxy cluster called Abell S1063 using JWST. The long exposure time, combined with the lensing power of the cluster, allows extremely faint sources in the background to be seen in unprecedented detail. The researchers scoured the data to search for signs of active black hole growth in the observed galaxies. Specifically, they carefully studied the emission lines in the spectrum of each object.

Normally, emission lines appear narrow. However, gas surrounding a massive black hole circulates at rapid speeds. A phenomenon known as the Doppler effect then comes into play. This is the same effect responsible for the characteristic rise and fall in the pitch of a siren from an emergency vehicle passing by. Emission from gas moving toward our line of sight appears bluer than it otherwise would, and gas moving away from us appears redshifted. The net effect is that a single emission line is widened, and we see characteristic “broad wings.” The width of the emission line can be used to estimate the mass of the central black hole, where broader wings imply a more massive black hole.

The researchers uncover 10 AGNs that display broadened Balmer series lines. Strikingly, they estimate that these galaxies have central black holes with masses as low as 400,000 times that of the Sun. While that might sound like a lot, it’s practically nothing compared to the monstrous 100-million-solar-mass black holes that JWST consistently turns up in other studies. Detecting such lightweight black holes, pushing into the realm of intermediate-mass black holes, is only possible due to the incredible sensitivity of these observations.

The researchers also compute what’s known as the black hole mass function. This is a measure of how many black holes exist at each mass. In other words, the black hole mass function measures how common lightweight black holes are compared to heavy ones. The mass function computed in this work and several other points of comparison are shown in Figure 1.

Figure 1: A comparison of black hole mass functions from various previous works and today’s article. The red hexagons are data points computed using the AGNs observed in this work, while blue circles and yellow squares are measurements computed using AGNs observed in previous articles. The red, green, and blue shaded areas represent the expected black hole mass function from various theoretical models. [Adapted from Fei et al. 2026]

Amazingly, this is exactly the measurement you would get if direct-collapse black holes (the hypothetical kind of massive black holes mentioned earlier in this article) were common in the early universe. If you scatter huge seeds across a large field, then you shouldn’t be surprised to see a sea of barely larger plants a few months later. Likewise, since these black holes start off so massive, they only need to grow a tiny bit to reach the threshold of that first red hexagon.

So is this proof that the early universe was filled with direct-collapse black holes, with this study probing the tip of an astonishing iceberg? It’s too early to tell for sure. While this is certainly an exciting result that sheds light on a previously unexplored population of objects, one can only do so much with a sample size of 10. More follow-up observations will be needed to measure the black hole mass function more precisely. Still, it’s amazing to think how much has changed in just a few years. JWST continues to provide unprecedented insight into some of the most breathtaking questions in all of astronomy.

Original astrobite edited by Tori Bonidie.

About the author, Ansh Gupta:

I’m an astronomy graduate student at the University of Texas at Austin working with Steven Finkelstein. I use data from JWST to study the formation and growth of the first galaxies and black holes in the universe. In my spare time, I enjoy playing piano, reading, and making YouTube videos.

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The image above shows a newly discovered molecular cloud. This cloud was discovered through the Milky Way Imaging Scroll Painting project, which uses a 13.7-meter millimeter telescope to survey molecular clouds in our galaxy. Xuepeng Chen (Purple Mountain Observatory; University of Science and Technology of China) and collaborators came upon this cloud in survey data from a region of the Milky Way opposite the galactic center. The newfound cloud is roughly 5,400 light-years away, spans an area of 245 by 294 light-years, and contains an estimated 80,000 solar masses. The most remarkable feature of the cloud is its structure: it appears to have a central cavity, an elliptical disk-like body, and spiral arms. Chen’s team has suggested that the cloud owes its surprising structure to density wave theory — the same process thought to govern the formation of spiral arms in galaxies — but other possibilities such as collisions between molecular clouds can’t yet be ruled out. To learn more about the properties of this unusual molecular cloud, be sure to check out the full research article linked below.

Citation

“Discovery of a Giant Spiral Molecular Cloud in the Galactic Anticenter,” Xuepeng Chen et al 2026 AJ 172 4. doi:10.3847/1538-3881/ae6800

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Editor’s Note: This week we’re at the 248th AAS meeting in Pasadena, CA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on Bluesky for more coverage. The usual posting schedule for AAS Nova will resume on 22 June

Table of Contents:

• Plenary Lecture: Ian Roederer, The Ultraviolet Path to the Origin of the Elements

Plenary Lecture: Ian Roederer, The Ultraviolet Path to the Origin of the Elements (by Susanna Kohler)

When the universe first formed, the only elements present were the three lightest — hydrogen, helium, and lithium. Today, there are 118 confirmed chemical elements that make up the periodic table. So where did the heavier elements come from, when were they first created, and what can they tell us about the first stars that formed in the universe? In the final plenary of AAS 248, Ian Roederer (North Carolina State University) walked us through how ultraviolet observations are the key to understanding the origin of the elements.

We know that hydrogen, helium, and lithium were cycled through the earliest stars in the universe, where fusion and other processes produced the first heavy elements that were spit back out into the cosmos when these stars ended their lives as supernovae. According to Roederer, within just the first two or three generations of stars, every element with stable or long-lived isotopes had already been created. For the heaviest of these elements, the dominant source is likely a process called r-process nucleosynthesis, in which a rapid burst of neutrons bombards atomic nuclei, resulting in the quick capture of the neutrons to form very massive nuclei that subsequently decay to stable isotopes.

Illustration of two neutron stars approaching a merger, emitting gravitational waves as they draw closer together. [ESO/L. Calçada/M. Kornmesser; CC BY 4.0]

But remember all those news headlines about how binary neutron star mergers produce gold and platinum? Roederer points out that these were all inferred results — we didn’t actually observe direct evidence of gold and platinum in the aftermath of this explosion. That’s because it’s very difficult to detect the spectroscopic emission lines of heavy elements. To do so effectively, Roederer argues, requires high-resolution ultraviolet (UV) spectroscopy. He showed that in a cool star, high-resolution UV spectra provide a 50% increase in the number of elements you can detect. The heaviest of elements are only detectable with spectra in the UV range.

An example spectrum for a second-generation star shows how the UV is critical for identifying a broad range of elements. [Roederer 2026]

Roederer ended his talk with a look ahead at the future of UV spectroscopy and the path to the universe’s first stars. Right now, the only mission we have that produces high-resolution UV spectroscopy is Hubble. NASA’s next big flagship mission with a high-resolution spectrograph, the Habitable Worlds Observatory (HWO), will be transformational in the ability to detect — or verify the absence of — heavy elements in stellar atmospheres. An observatory like HWO will provide our best shot at identifying low-mass, metal-free stars that survive from the first generation of stars in our universe. As Roederer concluded, “The future of studying the origin of the elements is bright in the UV.”

You can read Astrobites’s interview with Ian Roederer here.

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Editor’s Note: This week we’re at the 248th AAS meeting in Pasadena, CA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on Bluesky for more coverage. The usual posting schedule for AAS Nova will resume on 22 June.

Table of Contents:

• Plenary Lecture: Eliza Kempton, Common Worlds, Uncommon Complexity: Sub-Neptune and Super-Earth Atmospheres in the JWST Era
• Press Conference: Stars Reshaping Galaxies: Clusters, Feedback, and Explosive Aftermaths
• Plenary Lecture: George Helou, The Cosmic Infrared Window: Photons, Technology, and People
• Plenary Lecture: Carolyn Kuranz, Creating Astrophysical Conditions at High Energy Density Facilities
• Plenary Lecture: Cara Battersby, Our Galaxy’s Dynamic Center

Plenary Lecture: Eliza Kempton, Common Worlds, Uncommon Complexity: Sub-Neptune and Super-Earth Atmospheres in the JWST Era (by Lexi Gault)

Eliza Kempton began her talk addressing the undergraduates in the room, showing the meeting website from AAS 200, which she attended as an undergraduate in 2002. Searching this page, there were no presentations on exoplanets — a stark difference from the boom of exoplanet science that we see 24 years later at AAS 248, marking how significantly a field can transform from the start of your career.

Situating us outside of the solar system, Kempton showed the quintessential mass–period plot of all 6,000+ detected exoplanets thus far. Strikingly, we have discovered new types of planets that are not seen in our own solar system, but uncovering exoplanet populations is heavily skewed due to detection limits. While it is much easier to find large planets closely orbiting their stars, occurrence rate studies have shown that small planets on close-in orbits are much more common and typically come in two sizes: gas-rich sub-Neptunes and rocky super-Earths. However, actually deciphering their compositions relies on detailed studies of their atmospheres, which is the primary research work Kempton dove into.

How do we study exoplanet atmospheres? Thankfully, JWST provides the wavelength range and collecting area necessary for observing the minute details in exoplanet atmospheres. Beginning with sub-Neptunes, Kempton laid out four important takeaways from recent work coming from her team:

1. Sub-Neptune atmospheres composed of heavier elements and molecules are common.
2. Clouds and hazes are pervasive for planets that get a moderate amount of light from their host star. Early JWST observations showed signatures that may point to soot formation in sub-Neptune inner atmospheres; this soot can rise, making the upper atmosphere we observe hazy.
3. Sub-Neptune atmospheres may provide a window into their interiors. Observed atmosphere compositions may indicate no solid planetary surface, but rather magma, water, and/or gas that can mix more readily with the upper atmosphere.
4. Tying atmospheric observations to formation scenarios is still a challenge. Constraints on planets’ bulk composition has not provided clear answers.

Moving down to super-Earths, Kempton introduced the idea of the cosmic shoreline — the empirical relationship between planetary escape velocity and stellar irradiation shows a stark dividing line between planets with and without atmospheres in our solar system. Does this concept of a cosmic shoreline exist for exoplanets? Kempton highlighted three takeaways for the study of super-Earth atmospheres:

1. Spectroscopy of super-Earth atmospheres presents degeneracies in determining their characteristics. A featureless spectrum could be due to the presence of heavy molecules and clouds, or it could just mean the planet has no atmosphere.
2. Thermal emission is a powerful tool for identifying candidate atmospheres. The eclipse depth of a transiting planet is directly related to the day-side temperature of the planet. Planets with and without atmospheres will have different day-side temperatures — hotter without an atmosphere, cooler with an atmosphere.
3. Many (but not all) transiting super-Earths are bare rocks. 

Clearly, JWST has allowed astronomers to make significant progress in understanding exoplanet composition and subsequently their possible formation and evolutionary histories. Kempton ended with reminding us where we came from 24 years ago — the field of exoplanet science has boomed, and we can wonder how much we’ll continue to uncover in the next 24 years.

Return to Table of Contents.

Press Conference: Stars Reshaping Galaxies: Clusters, Feedback, and Explosive Aftermaths (Briefing video) (by Niloofar Sharei)

This press conference brought together four very different views of star-forming environments: the most distant galaxy cluster caught strongly lensing a background galaxy, the dense young star clusters tucked inside the rings of nearby galaxies, the extreme feedback physics inside the closest luminous infrared galaxy merger, and the first known pair of supernova remnants born from a binary star system.

A New Era of Galaxy Cluster Analysis at Cosmic Noon: JWST’s View of a Distant Galaxy Cluster

Kyle Finner (IPAC/Caltech), presented the discovery of strong gravitational lensing in XLSSC 122, the most distant known galaxy cluster, seen as it was about 10.3 billion years ago. When the team got their JWST imaging back, they noticed bright blue arcs around the brightest cluster galaxy, a clear signature of strong lensing from a background galaxy sitting in just the right place behind the cluster. Using those arcs, the team measured the radial dark matter profile and found that XLSSC 122 is much more centrally concentrated than cosmological simulations predict. To check whether the cluster itself is unusual, they combined the JWST result with multiwavelength data. All of those tracers show an elongated structure pointing the same way as the dark matter, which is a strong sign that XLSSC 122 is a merging cluster. But mergers usually lower concentration rather than boost it, so the question of why this early cluster looks so concentrated is still open. The team plans to follow up with more strong-lensing measurements. | Press release

This two-panel image shows a distant galaxy cluster as it has been observed by NASA’s Hubble Space Telescope and JWST. [NASA, ESA, CSA; Kyle Finner (Caltech/IPAC) Image processing: Robert Hurt (Caltech/IPAC-SELab)]

Sajia Shahrin Neha (University of Kentucky) presented a study of young massive clusters in the circumnuclear rings of two nearby galaxies: NGC 3351, a normal spiral, and NGC 1097, which hosts an active galactic nucleus. Young massive clusters are extreme star-forming systems that pack hundreds of thousands to millions of stars into a small region, and the ring-shaped star-forming zones around these galactic nuclei provide exactly the kind of dense gas and dust reservoir these clusters need. Because the clusters are heavily obscured, optical, ultraviolet, and infrared light cannot pass through cleanly, so Neha and collaborators turned to radio continuum imaging with the Atacama Large Millimeter/submillimeter Array and the Very Large Array, which can see through the dust. Their team identified 53 young massive cluster sources across the two rings. They also placed them on an evolutionary sequence: heavily embedded “starless” clumps, newborn clusters that are just starting to become visible, and older “exposed” clusters that have already burned through much of their gas. All evolutionary stages are present in both galaxies, regardless of whether the host has an active nucleus. | NRAO press release | U. Kentucky press release

Dusty and Over-Pressured: Measuring Stellar Feedback in the Closest Luminous Infrared Galaxy

Deb/Debosmita Pathak (The Ohio State University/IPAC) presented new measurements of pre-supernova stellar feedback in NGC 3256, the closest luminous infrared galaxy and a merger between two roughly Milky Way–mass galaxies. NGC 3256 forms stars about 60 times faster than the Milky Way, which makes it a useful nearby laboratory for the intense, clumpy star formation that dominated the early universe. Using JWST plus multiwavelength data, the team measured feedback pressures around roughly 1,700 young star clusters and compared them with what we see in quieter, normal star-forming galaxies. The results break the standard picture in two ways. First, the feedback and interstellar medium pressures in NGC 3256 are about a hundred times higher than what is typical in normal star-forming galaxies. Second, the dominant feedback mode is different: instead of warm ionized gas pressure doing most of the work, ultraviolet and infrared radiation pressure on dust dominates in these much dustier environments. Even at these much higher pressures, most clusters are still over pressured relative to their surroundings, meaning radiation is strong enough to drive expansion against a dense ambient interstellar medium. | NRAO press release | OSU press release

Unveiling the First Binary-System Supernovae

Miltiadis Michailidis (Kavli Institute for Particle Astrophysics and Cosmology (KIPAC)/Stanford University/SLAC National Accelerator Laboratory) closed the session with the discovery of what appears to be the first known supernova remnant pair born from a binary star system. The starting point is IC 443, one of the best-studied supernova remnants and one of the brightest gamma-ray sources in the sky, thanks to its interaction with a dense nearby molecular cloud. Recent eROSITA observations showed that the faint X-ray “shell” long noticed next to IC 443 is in fact a second, overlapping supernova remnant. The question was whether the two are physically related or just a chance alignment on the sky. They used 15 years of Fermi gamma-ray data and modeled and subtracted IC 443’s contribution and uncovered a distinct, hidden gamma-ray source associated with the new remnant.

The gamma-ray emission is strongly spatially segregated: its northern boundary, where it overlaps the same molecular cloud that IC 443 illuminates, is dominated by accelerated protons colliding with dense gas, while its southern boundary is dominated by accelerated electrons. The team also showed that the optical filament along the northern boundary is a radiative shock that has cooled past the point of efficient particle acceleration. Combined with the fact that both remnants sit at the same distance (about 6,000 light-years), and that a population-synthesis run with a million massive binaries reproduces the observed separation and age difference, the team argues that the two remnants are the remains of a true binary pair. | Press release

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Plenary Lecture: George Helou, The Cosmic Infrared Window: Photons, Technology, and People (by Kerry Hensley)

George Helou (Caltech) gave a sweeping overview of infrared astronomy over the past 40 years, including the impressive role of the Infrared Analysis and Processing Center, or IPAC, which is celebrating its 40th anniversary.

The infrared portion of the electromagnetic spectrum is broad, encompassing wavelengths from 1 to 1,000 microns. In that wavelength range, there’s a lot going on in our universe: redshifted emission from distant galaxies, stars revealed by the drop in dust extinction, rotational and fine structure lines, molecular transitions, and fully half of the radiation density in the universe.

An example of how infrared capabilities have improved over time. [NASA/JPL-Caltech; MIRI: NASA/ESA/CSA/STScI]

Helou introduced a few science areas in which infrared missions have contributed greatly. First was the study of polycyclic aromatic hydrocarbons (PAHs), which are a class of molecules containing interconnected rings of carbon atoms. Thanks to infrared instruments, astronomers showed that various unassigned spectral features arose due to PAHs and that these molecules were important for the heating and cooling of the interstellar medium. As infrared instruments became more capable, observations showed how the fraction of carbon that is locked up in PAHs changes with metallicity and revealed novel species like deuterated hydrocarbon nanoparticles.

In the field of exoplanets, IRAS found evidence of excess infrared emission around Vega, hinting at a disk of debris that was later confirmed. (IPAC was instrumental in this discovery; the star Vega was being used for calibration, and the calibration wouldn’t converge because of the unexpected infrared excess.) Later, ISO used spectroscopy to investigate stellar debris disks and showed that they were similar in properties to solar system comets. Though Spitzer wasn’t initially expected to be used for exoplanet studies, the telescope made the first detection of photons from the surface of a planet and helped to discover several planets in the TRAPPIST-1 system. (Here, IPAC played an integral role again; instrument teams and flight engineers worked to ready the spacecraft for exoplanet observations by modifying the heaters on the spacecraft for pointing stability and finding “sweet spots” for photometric stability.) Today, JWST continues to advance the field with sensitive measurements of exoplanet atmospheres.

Finally, Helou touched on the work that IPAC has done to archive data. IPAC maintains the NASA/IPAC Extragalactic Database, or NED, which receives at least three queries per second. It’s also responsible for the Infrared Science Archive, data from which is used in more than 50% of research articles. IPAC also manages the NASA Exoplanet Archive, showing that the center isn’t limited to infrared astronomy!

As for the future of IPAC and infrared astronomy, it’s clear that there is much left to explore and lots of exciting work to be done; the Roman Space Telescope is scheduled to launch in a few months, and within a few years the Near-Earth Object Surveyor will follow. The Ultraviolet Explorer, for which IPAC will provide the UVEX Science Data Center, is slated to launch in 2030, and the PRobe far-Infrared Mission for Astrophysics (PRIMA) is under final review.

Read Astrobites’s interview with George Helou.

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Plenary Lecture: Carolyn Kuranz, Creating Astrophysical Conditions at High Energy Density Facilities (by Lucas Brown)

While astronomy and astrophysics are often considered primarily observational sciences, with most targets of interest being millions to trillions of miles away from us — Carolyn Kuranz’s plenary talk helped to challenge this idea, demonstrating how we can sometimes bring the heavens down to Earth with high energy density (HED) facilities. The basic idea behind Kuranz’s work, and the field of HED laboratory astrophysics more broadly, is that some extreme astrophysical environments, particularly plasmas, can indeed be studied in the lab by producing smaller-scale analogs — so long as we choose the right types of experiments.

Kuranz structured her talk around three big questions she commonly gets asked about her field: firstly, why would astronomers want to do laboratory experiments? Then, what defines the “high energy density” in HED astrophysics? And finally, how do we actually do these experiments in practice? Starting with the why, Kuranz notes that studying systems in astrophysics is inherently difficult as a result of the fact that they are far away, and theoretical models can suffer from a lack of data or missing physics. Experiments can bridge the gap here, providing the ability to collect more data on specific systems of interest, complementing both theoretical models and observations.

While this philosophy can apply to a variety of laboratory astrophysics areas, such as laboratory-based studies of the chemistry of planetary atmospheres, Kuranz focused specifically on the emerging role of HED laboratory astrophysics. Typically, high energy density refers to systems with more than 1 million atmospheres of pressure and temperatures above 1 million K. Generally, this means we’re in plasma territory. In some ways, it’s only natural that studies of these sorts of environments would eventually help astrophysicists, given that around 99.9% of the matter in the universe is in plasma form. Despite this, the laboratory astrophysics side of HED physics has really only emerged over the past 30 years, with its origins being traced to work out of Lawrence Livermore National Lab, the current site of the National Ignition Facility (NIF).

Today, the NIF is only one of a few dozen facilities in which HED laboratory astrophysics experiments are conducted. This is because the type of equipment needed to reproduce environments analogous to various astrophysical systems can vary greatly. This gets to Kuranz’s third question of how these experiments are conducted. The process begins by answering a set of questions, including: do the astrophysical and proposed laboratory environments obey the same governing equations (conservation of mass, momentum, etc.)? Is one able to re-scale the physical parameters in each system (timescale, size, density, pressure, etc.) in a way that retains relevant dynamics like viscosity, Reynolds number, and so on? Once these details have been nailed down, a researcher can assess what types of facilities they may need. For example, the NIF, which uses symmetrical arrangements of lasers to compress and heat up millimeter-scale pellets containing gases that can undergo nuclear fusion, provides a fairly natural environment for studying processes in the cores of stars, which are also hot, dense, and neutron-rich environments where fusion is actively occurring.

As for the future, things look promising for HED laboratory astrophysics — since the NIF achieved “ignition” in 2022, producing a net gain of energy from one of these pellet-crushings for the first time, a huge amount of interest and investment has been flowing into facilities studying HED physics. These facilities range from private companies working to achieve sustained nuclear fusion power generation to longstanding federal research centers working on understanding nuclear weapons and stockpile management, but they all provide astronomers with the opportunity to do what was once unthinkable: bring the universe’s most extreme environments down to Earth.

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Plenary Lecture: Cara Battersby, Our Galaxy’s Dynamic Center (by Niloofar Sharei)

Cara Battersby (University of Connecticut) used her plenary to walk us through her group’s ongoing effort to understand one of the most extreme environments in our own galaxy: the central molecular zone (CMZ), which is a dense, turbulent gas reservoir at the heart of the Milky Way. Her talk pulled together large surveys, new high-resolution zoom simulations, and machine-learning methods designed to bridge between the two.

She opened with the PRobe far-Infrared Mission for Astrophysics (PRIMA), the far-infrared probe mission concept she is a co-investigator on. This mission concept was developed in response to NASA’s recent billion-dollar probe mission call, and selection is expected later this year. PRIMA covers roughly 1.8–25 microns with imaging and spectroscopy, and galactic ecosystems make up about a quarter of its science case.

Battersby paused mid-talk to speak directly to early-career people in the audience about work-life balance, including bringing her daughter and sister with her to the meeting, and the SPARK program at UConn that supports women and underrepresented groups in physics. Her message: astronomy should be done from a place of joy, and visible work-life balance is something the community should be more open about.

Battersby framed the Milky Way as the natural laboratory for star formation across a huge range of environments, and briefly reviewed the ALMAGAL survey, which observed roughly 1,000 high-mass star-forming regions across the disk. But her main focus was the CMZ, which she argued is essentially a different kind of galaxy embedded inside our own. About 80% of all the dense molecular gas in the Milky Way sits in the CMZ, and its gas properties — density, turbulence, temperature, and pressure — are extreme compared to the rest of the disk. Because nearby starburst and high-redshift environments share many of these properties, the CMZ is the closest place we can actually resolve individual star-forming cores under conditions that resemble the early universe.

She showed that gas in the CMZ is extremely filamentary across all scales, and that the relationship between dense gas and star formation rate is unusual: when individual clouds in the CMZ actually form stars, they form them much like clouds elsewhere in the galaxy, but a large fraction of the dense gas in the CMZ never engages in star formation at all. Battersby argued that this is likely because so much of that gas is being shaped by flows toward the black hole and the strong turbulence and dynamics of the central environment, and it never cools and collapses into stars.

She closed with the simulation and machine-learning side of the program. Her group runs zoom simulations that can follow individual star-forming regions and can resolve down to CMZ scales while still capturing the full ~5 kpc bar driving gas inward. To extract more from these simulations than just side-by-side image comparisons, the team built a GPU-accelerated radiative transfer code that runs roughly 10,000 times faster than existing codes. They generate hundreds of thousands of synthetic observations and use them to train an encoder–decoder convolutional neural network that learns to predict the top-down structure of a region from the side-on view we actually observe. Applied to the CMZ, the network produces 3D reconstructions that are physically plausible and broadly consistent across independent training runs.

Read Astrobites’s interview with Cara Battersby.

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Editor’s Note: This week we’re at the 248th AAS meeting in Pasadena, CA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on Bluesky for more coverage. The usual posting schedule for AAS Nova will resume on 22 June.

Table of Contents:

• Helen B. Warner Prize Lecture: Kyle Kremer, Globular Clusters: Astronomical Factories of Gravitational-wave and Electromagnetic Transients
• Press Conference: Our Changing Galaxy and the Skies We See
• High Energy Astrophysics Division Early Career Prize Lecture: Carolyn Kierans, Developing Next-Generation MeV Telescopes
• Press Conference: Fire and Ice in Planetary Systems Near and Far
• Solar Physics Division George Ellery Hale Prize Lecture: Yi-Ming Wang, The Sun as a Laboratory for Astrophysical Magnetic Fields
• Plenary Lecture: David Jewitt, The Interstellar Interlopers

Helen B. Warner Prize Lecture: Kyle Kremer, Globular Clusters: Astronomical Factories of Gravitational-Wave and Electromagnetic Transients (by Lucas Brown)

Kyler Kremer (University of California, San Diego) kicked off day two of AAS 248 with a “dynamic” talk on the complex interactions and environments that exist within globular clusters — the most massive category of stellar clusters, which can contain upwards of one billion stars. Because of the extreme stellar density of these environments, they are thought to be good factories of systems ranging from accreting white dwarfs to millisecond pulsars, which are often spun up to high speeds via accretion from companion stars. Such accretion, whether onto pulsars or other compact objects, can often generate bright X-rays, and as Kremer noted early on in his talk, it was in fact these X-ray sources that provided some of the earliest evidence of the abundance of exotic systems within globular clusters. By the early 2000s, hundreds of X-ray sources had been identified in globular clusters.

Along with these brightly emitting compact binary systems, we expect globular clusters to be home to a vast population of darker, more elusive objects — black holes. Kremer noted that because about one out of every thousand stars is thought to be massive enough to evolve into a black hole, older globular clusters are thought to produce tens or hundreds of thousands of black holes over time. These black holes are then expected to gradually sink towards the centers of the clusters through dynamical friction, where they will increasingly find themselves in the company of other black holes, or black hole binaries. As these massive objects swing by each other, they can occasionally merge or eject black holes out of clusters entirely. This leads to a complex evolutionary history, leaving many open questions in regards to how many black holes should persist in globular clusters today and with what properties.

Luckily, strong evidence for the presence of black holes in globular clusters began to come in around the early 2000s as a result of the direct measurements of stellar orbits around an invisible, at least 4-solar-mass object in NGC 3201. Since this discovery, multiple others have been made via similar techniques. The role of black holes in shaping our observation of globular clusters may go well beyond these isolated systems, however. Theoretical work has also shown that the presence of black hole binaries in the centers of globular clusters may contribute to dynamical heating of the overall cluster. This suggests that globular clusters that have not undergone core collapse, which represents over 80% of clusters, should retain significant black hole populations today.

While individual black holes can often be hard to spot, black hole binaries are becoming increasingly easy to hear, thanks to the advent of gravitational wave astronomy. At facilities like LIGO, Virgo, and KAGRA, merging black hole binaries are now regularly detected, creating a population-level catalog of black hole binary properties. While many of these systems can be well explained by black holes formed in the “isolated” channel, meaning originating from a preexisting binary star system, some mergers show signs of a “dynamical” formation history, which can arise in the sort of dense environments globular clusters provide. As one example, there seems to be more black holes in the 40-solar-mass and above range than many models predicted. At these high masses, more potential progenitor stars actually become too large to form black holes thanks to a phenomenon called pair instability. However, such massive black holes could be formed from the repeated mergers of smaller black holes — a hierarchical process that simulations have consistently shown can be highly efficient in globular clusters, especially the most massive ones. On top of this, Kremer noted that individual gravitational wave signals have recently shown other telltale signs of hierarchically formed binary black holes, such as asymmetric masses and spin–orbit misalignment.

Finally, Kremer turned to another class of exotic astrophysical objects to explore other ways globular clusters can generate interesting phenomena: pulsars. Pulsars, like black holes, form from the collapse of massive stars. This rapidly rotating sub-category of neutron stars beams radiation from their poles, which gradually slows them down and depletes the strength of their radio emission over millions or billions of years. Because of this, one would expect older globular clusters to have a slowly rotating and mostly invisible population of pulsars. Instead, we see many rapidly rotating millisecond pulsars in these environments, suggesting that the dense cluster environment allows for many of these systems to be spun back up through accretion from other stars. In contrast, we also see young globular clusters which contain slowly rotating pulsars — another puzzle, yet one that may again be explained by the dense environment. Some researchers believe that these pulsars are formed via the direct merger of multiple white dwarfs, rather than from the collapse of a massive star. Such systems may also be the source of some fast radio bursts; the first fast radio burst associated with a globular cluster was discovered in 2020. It seems like globular clusters may be the gift that just keeps on giving!

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Press Conference: Our Changing Galaxy and the Skies We See (Briefing video) (by Niloofar Sharei)

This press conference walked through four very different ways our view of the Milky Way and our skies are changing right now — from extreme gas physics at the Galactic Center, to the hidden stellar populations of a cluster, to the rapid flickers of dying stars, and finally, to a very practical question: what are dark night skies actually worth to the public?

Resolving the Supersonic-to-Subsonic Gas Transition in the Galactic Center for the First Time

The galactic center and the surrounding central molecular zone make up the most active star formation region in the Milky Way. [NRAO/AUI/NSF; CC BY 4.0]

Buddhacharya mapped how gas transitions from highly turbulent, supersonic motion to calmer, subsonic motion across a region in the CMZ. This transition is well known in nearby clouds, where it usually precedes gravitational collapse, but it had never been clearly resolved in the CMZ before. Their team found a “calm island” of subsonic gas embedded in the otherwise turbulent sea. This is the first observation of its kind in the galactic center.

The Multi-Age Stellar Populations of Terzan 5 as Revealed by JWST

R. Michael Rich (University of California, Los Angeles) presented new JWST and Hubble Space Telescope observations of Terzan 5, an unusual stellar system near the center of the Milky Way that looks like a globular cluster but doesn’t act like one. Earlier work had already shown that Terzan 5 hosts at least two distinct stellar populations with very different ages and chemical abundances, which is unusual for a typical globular cluster.

Because Terzan 5 sits behind a thick screen of foreground stars and dust, separating real cluster members from contamination is one of the hardest parts of the analysis. The team combined JWST and Hubble imaging to measure stellar proper motions, then used a vector point diagram to isolate the stars that move together with the cluster. They identified two additional stellar populations beyond the two already known. Rich argued that Terzan 5 may be a “fossil fragment,” possibly the leftover core of a small galaxy or early bulge structure that was accreted long ago.

Sub-Day Periodic Variability of Two Central Stars of Planetary Nebulae

Gaoyang Du (Dalian University of Technology) reported the discovery of new short-period signals in the central stars of two planetary nebulae. These central stars are the hot, exposed cores left behind by Sun-like stars at the end of their lives, and finding rapid brightness variations in them tells us about their interior structure and pulsation physics.

Short-period signals well under a day are very hard to recover from the ground because Earth’s rotation introduces strong one-day aliasing, so the team turned to the Transiting Exoplanet Survey Satellite, which observes continuously from space. Using a neural-network pipeline designed to handle the crowded, contaminated backgrounds these stars sit in, they recovered the previously known variability in NGC 1501 and detected a new signal at roughly half an hour. Follow-up spectroscopy will be needed to pin down whether the signals come from pulsations, rotation, or something else, but the result opens a new window on the rapid variability of dying-star cores.

Artificial Light at Night Significantly Degrades the Value of Public Lands

Jordan Smith (Utah State University) closed the press conference with a very different kind of measurement: the economic value of dark night skies. While astronomers usually treat light pollution as an observing problem, Smith and his collaborators are asking what the public is actually losing and what people would pay to keep dark skies on public lands. The team surveyed 634 visitors across International Dark Sky-certified parks, asking detailed questions about visitation behavior, motivations, and willingness to pay. Combining those surveys with satellite-based sky-brightness data, they estimated how the actual darkness of a site translates into the value visitors place on a trip. Based on the survey results, they found that visitors were willing to pay $45 more per visit to go to a park with skies one level darker on the Bortle scale. That sounds small per visitor, but scaled across all visits to all dark-sky public lands, it represents a very large economic value tied to a public good that current policy frameworks rarely account for.

An illustration of the Bortle scale, which quantifies the degree of light pollution at a given location. [ESO/P. Horálek, M. Wallner; CC BY 4.0]

High Energy Astrophysics Division Early Career Prize Lecture: Carolyn Kierans, Developing Next-Generation MeV Telescopes (by Niloofar Sharei)

Carolyn Kierans (NASA Goddard Space Flight Center) was awarded the AAS High Energy Astrophysics Division Early Career Prize for her work on developing the next generation of megaelectronvolt (MeV) gamma-ray telescopes. Her talk laid out why the MeV band is so valuable (it contains nuclear emission lines like the 511 keV positron-annihilation line that traces high-energy processes in our galaxy) and why it has been so technologically difficult to observe well, since photons at these energies do not focus easily and the dominant interaction in the detector is Compton scattering. She walked through her work using balloon-borne Compton telescopes to mature the technology, the tools her team has developed in recent years to improve event reconstruction, and the broader roadmap for the next generation of MeV instruments.

Read Astrobites’s interview with Carolyn Kierans.

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Press Conference: Fire and Ice in Planetary Systems Near and Far (Briefing video) (by Kerry Hensley)

An image from the Galileo spacecraft of a volcanic plume on Jupiter’s moon Io. [NASA/JPL/University of Arizona]

The team modeled Io’s plumes in order to explain the moon’s lack of impact craters, understand how certain plumes have persisted on Io for more than 45 years, and motivate a possible mission concept that includes a plume flythrough and sample return. They modeled the formation of ash as magma rises in a volcanic vent as well as the trajectory of the ash once it’s ejected into the plume, aiming to 1) match the plume observations from the Galileo spacecraft and 2) understand how an ash-filled plume might look different from one filled only with sulfur dioxide. While Turner found that Galileo data couldn’t discern between the two scenarios, ash makes a dramatic difference at the sub-millimeter wavelengths accessible to the Atacama Large Millimeter/submillimeter Array, which the team hopes to use to test this prediction. Finally, returning to the development of the mission concept, Turner proposed using a probe to first fly through the shadow of a plume to assess the particle size before sending the spacecraft through to collect a sample.

Up next, Tunhui Xie (University of California, Los Angeles) turned to Io’s neighbor, Europa. Europa and the other large icy moons of Jupiter are of interest to researchers because they might have subsurface oceans. Observations of Europa from ~30 years ago show that the moon has strange radar properties: its radar albedo is large, and the return signal retains the strong circular polarization of the outgoing signal.

To investigate the moon’s radar weirdness further, Xie’s team observed Europa from 2011 to 2024 and showed that the moon’s albedo (fraction of light reflected from its surface) is roughly constant with longitude. There is some evidence of differences between Europa’s hemispheres, which could be a sign of spiky ice structures called penitentes protruding from the frosty surface; Europa’s trailing hemisphere might be subjected to more particles from Jupiter’s magnetosphere, which could suppress the growth of penitentes in that region and cause a difference in the albedo. Xie also addressed the polarization behavior of the radar signal, showing that this is likely due to the coherent backscatter opposition effect. Finally, Xie showed how observations helped to place an upper bound of 32 meters for the penetration depth of X-band radar photons into Europa’s icy shell.

Penitentes in the Atacama Desert. [ESO/B. Tafreshi (twanight.org); CC BY 4.0]

In some of the earliest spectroscopy taken by a large-aperture telescope, Bolin’s team found cometary volatiles like CN, but not C₂ or C₃, which are common in comets, giving them a green color. These missing species emerged a couple of months later, which coincided with the comet taking on a greener appearance. As the comet retreated from its encounter with the Sun, these emission features faded. This presentation by Bolin showed how early and continuing monitoring of an interstellar object by a large-aperture telescope can reveal how these objects are affected by their journeys through our solar system.

Moving out of the solar system entirely, Tiffany Kataria (NASA JPL/Caltech) turned the discussion toward exoplanets. Kataria discussed HD 80606b, a 4.1-Jupiter-mass planet on an extremely eccentric (e = 0.93) orbit with a period of 111 days around a solar-type star. Kataria used JWST to observe HD 80606b’s phase curve, which revealed different parts of the planet as it travels along its orbit. Each time the planet makes its extremely close approach to its host star, it gets “flash roasted” and experiences a rapid increase in temperature. This rapid heating event is complex, depending on factors like the planet’s atmospheric chemistry and winds. The JWST data revealed that HD 80606b’s temperature skyrockets an incredible 1,100℉ over the course of its orbit. There’s still much more to learn from the rich spectroscopic dataset from JWST, so keep an eye out for more findings about this flash-roasted exoplanet in the future!

Finally, Aurora Kesseli (IPAC/Caltech) discussed another toasty exoplanet called CoRoT-2b, which is a hot Jupiter on a 1.7-day orbit around its star. Because hot Jupiters orbit their hosts so closely, astronomers expect all of these extreme exoplanets to be tidally locked, with one side of the planet perpetually facing the star and the other side in perpetual darkness. However, CoRoT-2b might be breaking that trend. In 2018, researchers reported that CoRoT-2b had winds that blew in the opposite direction from all other known hot Jupiters. They drew this conclusion from the location of the hottest point on CoRoT-2b, which appeared just after the planet ducked behind its star, rather than just before — unlike all other hot Jupiters studied so far. At the time, researchers hypothesized that the unusual location of the hotspot was due to clouds on one side of the planet, a magnetically induced westward wind, or a lack of tidal locking.

Using new data from the Very Large Telescope and Gemini South, Kesseli found that the planet’s strange properties can be explained best by a lack of tidal locking. CoRoT-2b appears to rotate at 2.24 km/s — far slower than the 4.37 km/s expected if the planet were tidally locked. There are no theories yet that explain why CoRoT-2b wouldn’t be tidally locked, so it remains a mystery for now!

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Solar Physics Division George Ellery Hale Prize Lecture: Yi-Ming Wang, The Sun as a Laboratory for Astrophysical Magnetic Fields (by Kerry Hensley)

Yi-Ming Wang (Naval Research Laboratory) gave the AAS Solar Physics Division’s George Ellery Hale Prize Lecture for “sustained, foundational contributions to understanding solar magnetism, the solar cycle, and the solar wind.” Wang is perhaps most known for the Wang–Sheeley–Arge solar wind model, which is widely used in space weather forecasting.

Wang began by musing on how his winding career path brought him to solar physics. Initially a theorist who modeled neutron stars, Wang was later hired to do radio astronomy but arrived for the position later than expected, so he was roped into working on solar physics instead — where he learned many things about magnetic fields that he wished he’d known when working on neutron stars!

This 19.3-nanometer image, taken by the Solar Dynamics Observatory on 11 December 2023, shows at the center of the Sun’s disk the remnant of a large coronal hole. [NASA/SDO and the AIA, EVE, and HMI science teams]

Next, Wang discussed the source of coronal heating. The solar corona is famously extremely hot, running at a few million degrees compared to the ~6000K solar photosphere. For decades, the Parker nanoflare model has been the leading explanation for how the corona gets so hot. In this model, the places where coronal loops touch down in the solar photosphere are continually wiggled around by random motions of the photosphere, which tangles up the magnetic field lines in the coronal loop. When the current sheets in this system dissipate, the corona is heated. Instead, Wang favors an observationally based model in which the heating comes from magnetic reconnection with underlying small-scale fields.

Finally, Wang briefly touched on the connection between the Sun’s magnetic field and the speed of the solar wind. The solar wind has been measured at Earth since the 1960s, and these measurements have shown that the mass and energy flux density of the solar wind scales with the strength of the footprint magnetic field strength, but the observed solar wind speed is independent of the footprint field strength. Instead, the speed scales inversely with the rate of magnetic flux-tube expansion in the corona. Thus, the solar wind speed at Earth can be calculated from the rate of flux-tube expansion along open magnetic field lines using maps of the photospheric magnetic field.

In the end, Wang’s work on the solar magnetic field did connect back to his earlier work in high-energy astrophysics, with relevance to period changes in binary pulsar systems and other areas. Magnetic fields really do connect all parts of astrophysics!

Read Astrobites’s interview with Yi-Ming Wang.

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Plenary Lecture: David Jewitt, The Interstellar Interlopers (by Niloofar Sharei)

David Jewitt focused his plenary talk on a rare kind of small body: the three confirmed interstellar objects that have passed through the solar system so far. He opened with the Oort cloud as a framing device. Comets in the Oort cloud did not form there — they formed near the giant planets and were scattered out by gravitational interactions. The same process leaks comets to interstellar space very efficiently: only about 1–10% are trapped into a star’s own Oort cloud. Across the galaxy, that implies a free-floating population on the order of 10²⁴–10²⁵ objects. Seeing some of them pass through our solar system is exactly what we should expect.

Artist’s impression of the first known interstellar object to visit our solar system. ʻOumuamua. [ESO/M. Kornmesser; CC BY 4.0]

Jewitt then turned to what the three objects tell us as a population. The strongest constraint comes from ʻOumuamua, precisely because its discovery was such a near miss: catching one in that brief visibility window implies roughly 1,000 similar objects crossing the solar system per year. The three objects look very different in size, activity, and composition, which is consistent with sampling a broad galactic population, and their velocity dispersion lines up with the disk-heating picture, in which older galactic populations are kinematically hotter. The leading origin story is the same one he set up at the start: scattering from the protoplanetary disks of giant planets around other stars.

Read Astrobites’s interview with David Jewitt.

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Editor’s Note: This week we’re at the 248th AAS meeting in Pasadena, CA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on Bluesky for more coverage. The usual posting schedule for AAS Nova will resume on 22 June.

Table of Contents:

• Fred Kavli Plenary Lecture: Richard Teague, Revealing the Dynamics of Planet Formation
• Press Conference: The Science of Stellar Remnants
• Plenary Lecture: Sanmi (Oluwasanmi) Koyejo, The Measurement Gap: What AI Can Get Wrong and Why Astronomers Are the Fix
• Press Conference: Variable, Windy, and Disruptive: The Behavior of Supermassive Black Holes
• Plenary Lecture: Mario Juric, Early Results from the Rubin Observatory: Mapping the Solar System and Beyond
• Plenary Lecture: Esra Bulbul, Cosmology and Baryons Across Scales: Probing Halo Mass Function to Cosmic Filaments with eROSITA

Fred Kavli Plenary Lecture: Richard Teague, Revealing the Dynamics of Planet Formation (by Lexi Gault)

Richard Teague (Massachusetts Institute of Technology) gave the Fred Kavli Plenary Lecture on his groundbreaking work in the dynamics of planet formation. The study of planet formation, as Teague introduced, has advanced significantly in the last two decades with the discovery of thousands of exoplanets and the launch of cutting-edge instruments. While planets are found everywhere orbiting a wide variety of stars, not all planetary systems look the same. Our solar system looks very different from other exoplanetary systems, challenging our understanding of planet formation and requiring us to build a picture that works across the board.

Where do we look to build a better understanding of planet formation? Planets are inherently the byproduct of star formation, forming in protoplanetary disks around new stars. These disks are filled with gas and dust, concentrating mass into rings that then eventually form planets. Exactly how this process proceeds is variable, and the resulting planetary system depends on how the material in the protoplanetary disk mixes and combines into planets. Teague compared planets to bread: we know the simple list of ingredients that it takes to make them, but what you end up with depends on how you bring those same ingredients together. We need to study what is happening in the planetary mixing bowls to understand how planets form.

The full exoALMA sample. All 15 disks show evidence of substructure in their gas emission. [Teague et al. 2025]

The first science results from exoALMA have started to reveal that the planet formation process is highly dynamical — precise kinematic measurements uncover dynamical perturbations within protoplanetary disks across their sample. These perturbations point to the impacts protoplanets have on disk kinematics and mass distributions as they continue to form, and the high resolution of ALMA observations unlocks the inner workings of protoplanetary disks.

Looking forward, Teague emphasized that the future is broad for planet formation science. The upcoming Wideband Sensitivity Upgrade on ALMA will enable even more detailed maps of protoplanetary disks, unlocking the mysteries of planet formation while it happens.

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Press Conference: The Science of Stellar Remnants (Briefing video) (by Lucas Brown)

In AAS 248’s very first press conference session, we heard from a variety of scientists and research teams on all sorts of stellar remnants: white dwarfs, supernovae, pulsars, and beyond. Basically, if it came from a dying star, it was fair game for this session.

Boron and Beryllium as Unlikely Probes of Extrasolar Planets

First up was Ben Zuckerman (University of California, Los Angeles), who updated us on ongoing research into the presence of boron and beryllium in certain white dwarf systems. For some context, there exist many white dwarf systems in which a companion object — sometimes a planet — can have its material accreted onto the surface of the white dwarf due to tidal disruption during close approaches in its orbit. This deposition of material can then be detected via spectral signatures in observations of the white dwarf.

In 2021, evidence was first presented for two white dwarfs being “polluted” with trace amounts of beryllium, which is a particularly rare element, cosmically speaking. This raises the question of how so much beryllium ended up in these systems. In the hunt for answers, however, another mystery has emerged: missing boron. As Zuckerman went on to describe, boron was also recently discovered in some of these white dwarf systems, but at an abundance roughly equal to that of the beryllium. This is despite boron being about a hundred times more common in the universe, further muddying the waters of what exactly is causing such a strange pattern of heavy metals in these systems. Work remains ongoing to find a physical model that can reconcile these observations.

White Dwarf Kicks via Episodic Mass Ejection from Red Giant Stars

In the model explored by Jim Fuller and collaborators, repeated mass-ejection events can cause red giant stars to be “kicked” up to a relatively high velocity before they collapse to form white dwarfs, explaining the high velocities many white dwarfs are observed to have. [Jim Fuller]

Additionally, this random ejection process predicts that red giants in binary systems will experience a sort of “random walk” in their orbital parameters, not just their overall velocity. This can lead to the complete dissociation of binaries, or to the direct collision of a red giant with its companion — leading to predictions about how many widely spaced white dwarf binary systems should exist. | Press release

Probing Intrabinary Material in a New Spider Millisecond Pulsar

Rebecca Kyer (Michigan State University) gave an update on research into so-called “spider” millisecond pulsars. These rapidly rotating neutron stars are a sub-class of pulsar characterized by their very high spin rate and the presence of a companion from which the pulsar is accreting material. Such systems are further sub-classified as either “Black Widows,” which have very low-mass companions (~3% solar mass), “Redbacks,” which have larger companions at ~10-80% solar mass, and “Huntsmans,” which have more massive red-giant companions. These Huntsman pulsars are the newest category, with only two known cases — until now!

Kyer presented evidence collected by their team that may indicate the discovery of a third Huntsman pulsar. The evidence involves radial velocity measurements of the companion star, which shows an orbital period of 3.64 days and variable H-alpha emission. In these systems, the radio emission typically associated with the pulsar can be blocked from our view for unpredictable amounts of time due to clouds of hot gas and dust that emerges from the complex interaction between the pulsar and red giant winds. Despite this, Kyer hopes that with enough targeted observations with the Green Bank Telescope, a radio signal will eventually be detected, confirming the pulsar’s presence.

Image of Messier 83 in both X-ray and optical light. Prominent X-ray sources can be seen as small colorful blobs strewn throughout the galaxy. Some of these X-ray sources are supernova remnants, a subset of which have recently been found to show variability in their brightness. [X-ray: NASA/CXC/SAO; Optical: NASA/ESA/AURA/STScI, Hubble Heritage Team, W. Blair (STScI/Johns Hopkins University) and R. O’Connell (University of Virginia); Image Processing: NASA/CXC/SAO/A. Jubett, L. Frattare and P. Edmonds]

Finally, we heard from a team of three researchers — Andrea Prestwich (Catholic University of America / NASA Goddard SFC), Roy Kilgard (Wesleyan University), and Zoe Hoiland (Vassar College) — on an unexpected supernova discovery. Traditionally, supernovae are modeled as having a relatively constant or slightly decreasing luminosity, at least after their initial explosion. As the stellar material is blasted away from the progenitor’s core, it interacts with the surrounding interstellar medium and a blob of hot, shocked gas is left over. This blob will eventually cool and dim, but often over a long time period, leading to the aforementioned prediction of constant or slightly decreasing brightness.

However, in 14-year Chandra observations of a supernova remnant in Messier 83, Prestwich and her collaborators actually found significant X-ray variability, with the remnant occasionally even increasing in brightness. In a follow-up study, it was found that supernova remnants in Messier 51 likewise show this up-and-down variability. In contrast, an analysis of remnants in Messier 101 showed zero variable remnants. Notably, the former two galaxies are very actively star-forming, while the latter is not. Some possible theoretical models to explain this variability include the possibility of stellar material falling back on the compact object leftover by the supernova, creating an accretion disk that can generate variable emission. Alternatively, it has been proposed that there could be a neighboring star to the remnant object, forming an accreting X-ray binary system that could also induce variability. | Press release

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Plenary Lecture: Sanmi (Oluwasanmi) Koyejo, The Measurement Gap: What AI Can Get Wrong and Why Astronomers Are the Fix (by Lexi Gault)

Sanmi (Oluwasanmi) Koyejo, a professor of computer science at Stanford University, focused this plenary talk on the limitations of AI as it becomes more integrated with science and how astronomers can help solve these problems. Koyejo began by addressing the question of why an AI researcher is talking to astronomers. His research explores how to set AI standards and how to best assess the performance of an AI model, which becomes particularly important when these models are used to do science.

Evaluating the performance of an AI model relies on benchmarks, a fixed set of questions with known answers that are used to score the AI. These benchmarks are simple, reproducible, and comparable, but passing a benchmark does not equate to getting a meaningful scientific result. Benchmarks assume cheap checks, fast feedback, and fixed questions, but science is none of those things; answering astronomy questions relies on telescope time, and ground truth cannot be found quickly.

Much like telescopes, AI benchmarks are measuring instruments with noise that can compound. If you run an AI model many times, the goal is often convergence on an agreed-upon answer, but getting to an agreed-upon answer does not mean that the answer is correct. Koyejo’s recent research found that AI models more often agreed with each other than they did with the actual truth. This is made worse when AI is used to evaluate itself. For example, Koyejo notes the rising number of academic paper submissions due to AI-written papers greatly exceeds the capacity of human reviewers. If AI tools are used to evaluate AI-generated paper submissions, the AI will tend to favor AI-written materials, ignoring the actual scientific merit. Making evaluation of AI an AI problem compounds its failures, straying further from a correct answer.

This is where astronomers come in. Having the expert knowledge of what “correct” looks like, being able to judge which errors matter, access to expensive ground truth (telescope time), and a culture of blind analysis (not knowing exactly what the answer should be), astronomers are well equipped to build standards for AI evaluation. We can define what good AI is for astronomy and use our expertise to help build the standards. Koyejo left the audience with the charge to engage with AI (engagement does not mean endorsement), so that astronomers can help set the standards for appropriate AI use in science.

Read Astrobites’s interview with Sanmi Koyejo.

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Press Conference: Variable, Windy, and Disruptive: The Behavior of Supermassive Black Holes (Briefing video) (by Niloofar Sharei)

This press conference focused on what supermassive black holes do to the world around them, from relativistic jets of the most famous black hole, to the multi-phase winds launched from active galactic nuclei, to temperature-shifting coronae, and even the radio burps that are produced years after a black hole tears apart stars.

Chandra Tracks the Evolving Jet from Messier 87’s Black Hole: 

Camille Poitras (Laval University) presented the largest Chandra X-ray movie of jet evolution in the famous supermassive black hole Messier 87 (M87). M87 has been studied across the electromagnetic spectrum, but X-ray observations of its jet have always suffered from blur because high-energy photons are hard to focus. Using improved Chandra calibrations and deconvolution techniques, the team produced a 13-year X-ray movie of M87’s jet from 2012 to 2025. Tracking a bright knot within the jet, Poitras’s team saw it split into two components in 2023, with one component moving at an apparent five times the speed of light (which is a known illusion called superluminal motion). That allowed the team to look into where and how the particles are being accelerated to extreme energies along the jet. | Press release

Watching a Black Hole Wind Grow: Chandra and Hubble Reveal the Early Stages of Galaxy

Multiwavelength images of two nearby quasars show that the hot X-ray (red) and warm ionized (green) gas are far more extended in the bottom system. Click to enlarge. [Anna Trindade Falcao]

The three types of wind launched from an accreting supermassive black hole. Click to enlarge. [Xin Xiang]

Xin Xiang (University of Michigan) presented the most detailed X-ray portrait of the winds flowing out of NGC 4151, an active galaxy roughly 16 million light-years away with a 30-million-solar-mass black hole. Every major X-ray observatory has observed this galaxy before, but earlier instruments could not separate its multiple wind components. With the high-resolution X-Ray Imaging and Spectroscopy Mission (XRISM) spectrometer, Xiang resolved three wind populations by velocity: warm absorbers (100–1,000 km/s), very fast outflows (1,000–10,000 km/s), and ultra-fast outflows (over 10,000 km/s). Across 14 XRISM observations over a year, they found that the fast winds turn on three hours after each bright X-ray flare, matching the predicted timescale for magnetically driven wind. | Press release

NuSTAR Reveals a Significantly Variable Active Galactic Nucleus Corona

Xiurui Zhao (Caltech) presented the first observational evidence of significant temperature variation in the corona of an AGN. The corona produces about 90% of all X-ray photons from an AGN, but its temperature can only be measured with X-ray missions sensitive to high-energy spectral curvature like NASA’s NuSTAR. They compared NuSTAR’s observations across multiple years and found that despite having the same luminosity in 2015 and 2024, the 2024 corona was significantly cooler than the 2015 corona. In follow-up observations in 2025, it was back at its earlier temperature. This is the first clear observation of coronal temperature variability in an AGN. | Press release

New Surprises from Radio Observations of Tidal Disruption Event Outflows

Kate Alexander (University of Arizona) presented new radio observations of tidal disruption events (TDEs). TDEs occur roughly once every 100,000 years in a given galaxy. It happens when a star drifts too close to the black hole, is stretched and squeezed into a long stream of debris (a process astronomers call spaghettification) and some of that debris falls onto the black hole while the rest is thrown outward and lights up in radio. Alexander and her team used six years of Very Large Array monitoring of several dozen nearby TDEs. They found that many TDEs unexpectedly turn on in the radio years after the original event, even long after their optical light has faded. Their team combined radio data with X-ray and optical accretion-rate measurements and found that these late-time radio flares appear when the black hole is eating either very quickly or very slowly, but not at moderate rates! This pattern matched what is seen in stellar-mass black holes and this suggests that accretion physics may operate similarly across many orders of magnitude in black hole mass. | Press release

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Plenary Lecture: Mario Jurić, Early Results from the Rubin Observatory: Mapping the Solar System and Beyond (by Kerry Hensley)

Mario Jurić (University of Washington; PI of the University of Washington Rubin operations element) began by remarking on how our collective concept of what an astronomer is has been transformed over the past 25 years. While a Google image search for “astronomer” yields an array of people pointing small telescopes at the night sky, today’s version of professional astronomy looks quite different: huge telescopes with enormous cameras covering vast swaths of the sky, with analysis aided by software and data deposited in massive databases.

This rapid transition was first spurred by enterprises like the Sloan Digital Sky Survey, which collected 20 terabytes of raw data from 1.2 billion observations. Now, digital sky surveys are common, and they’re becoming ever larger. The next massive digital sky survey will be the Legacy Survey of Space and Time from the NSF–DOE Vera C. Rubin Observatory — an observatory that can “download the universe” and is poised to transform our understanding of everything from asteroids to dark energy.

Rubin released its first images on 23 June 2025, and among these stunning images is a broad view that contains thousands of galaxies in the Virgo cluster, a golden tangle of four colliding galaxies, a nearby galaxy cluster, a distant galaxy cluster, and a handful of nearby spiral galaxies bursting with star formation. As fantastic as this image is, Jurić emphasized that it’s just one still image in a movie: as Rubin returns to the same fields of view time and time again, it’ll spot things that change brightness (like variable stars and transients) and things that move (like asteroids).

Jurić highlighted four areas in which Rubin has already contributed greatly, focusing on discoveries within our solar system:

1. 1. Asteroid variability: Rubin has already collected hundreds of thousands of observations of asteroids, resulting in the discovery of extremely fast rotators like 2025 MN45, which must have an extremely high tensile strength not to fly apart.
   2. Observations of interstellar object 3I/ATLAS: During the observatory’s commissioning survey, the Rubin team realized that they had observed 3I/ATLAS before it was discovered — but in observations that were technically under embargo. Recognizing the high impact of the data, the team found a way to share their findings, leading the 150-person collaboration to write a paper on their findings in a mere three days.
   3. High-precision asteroid photometry: While analyzing the commissioning data, the Rubin team discovered systematic offsets in the positions of asteroids — but no other types of objects. They found that this effect varied across the sky and was worse in the south. They eventually discovered that because most asteroids are observed from the north, that catalogs of asteroid orbits are systematically biased at a level of 20-40 milliarcseconds. Luckily, Rubin will provide the much-needed southerly data necessary to clean up these catalogs within about a year.
   4. Outer solar system studies: Researchers discovered 380 new trans-Neptunian objects in Rubin’s commissioning data. (Compare that to just 5,000 known trans-Neptunian objects in total!) In the time since the commissioning data were collected, hundreds more candidate objects were discovered.

With such enormous data yields from Rubin, how do we efficiently turn data into science? Jurić outlined strategies for handling massive datasets using well-crafted data formats, computing tools, and AI. In particular, Jurić highlighted the Astronomical Catalog Inference Driver, or ACID, which he built in four weeks on his phone using Claude. The tool is comparable to “a product developed in >3 years by extremely capable human professionals” and can rapidly handle immense data tables, showing how AI can accelerate the development of tools to handle tomorrow’s datasets.

Read Astrobites’s interview with Mario Jurić.

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Plenary Lecture: Esra Bulbul, Cosmology and Baryons Across Scales: Probing Halo Mass Function to Cosmic Filaments with eROSITA (by Lexi Gault)

Esra Bulbul (Max Planck Institute for Extraterrestrial Physics) began her plenary talk at the beginning of time — the Big Bang marked the start of the universe, and from there we attempt to constrain cosmological parameters in order to understand how the universe was born and how it has evolved. Bulbul notes that a lot of work has been done to constrain cosmology from the cosmic microwave background (CMB), and we must compare those early time measurements to those from later times to build a full picture. In cosmology, tensions have arisen between early-time and late-time probes. CMB measurements of the Hubble constant and S8, the “clumpiness” parameter of the universe, do not agree with late time probes that find that the universe is accelerating faster with smaller fluctuations than the CMB predictions. How do we work toward resolving this tension?

The extended ROentgen Survey with an Imaging Telescope Array (eROSITA) is a space telescope that has performed the first imaging all-sky survey in the medium X-ray range, seeking to map the large-scale structures of the universe to better constrain cosmological constants. eROSITA focuses on finding galaxy groups and clusters via the hot X-ray gas within and between them across the last 5-7 billion years of the universe. Since its launch in 2019, eROSITA has completed more than four full-sky surveys. Of the million X-ray sources detected by eROSITA, only 12,247 (1%) are galaxy clusters and groups.

From the observed X-ray emission from the galaxy clusters and groups, the eROSITA team has been able to measure the temperature of the intercluster medium within the sample. Working with weak gravitational lensing surveys, they have been able to measure the masses of the newly discovered clusters and groups. These measurements show that eROSITA has detected sources across three orders of magnitude in mass, reaching from the galaxy level to large-scale clusters.

The galaxy cluster and group observations allow them to constrain a few cosmological parameters including S8 (density fluctuations), Ωm (matter density), and w0 (dark energy). From the impressive eROSITA data, Bulbul showed that they could constrain S8 and Ωm to five times better precision than ever before! These late-time results are fully consistent with what has been measured from the early-time CMB measurements. Additionally, the dark energy measurements agree with what has been measured thus far from the Dark Energy Spectroscopic Instrument survey.

Bulbul then switched us from the exciting cosmological results to those regarding baryon detection. A striking result from eROSITA was the detection of hot gas well beyond what is typically considered the gravitational extent of a galaxy cluster — reaching out to 16 million light-years, often larger than the galaxy cluster itself. This underscores the importance of X-ray surveys in detecting the very extended gas encapsulating the largest-scale structures of the universe.

Looking forward, Bulbul discussed the future work planned for eROSITA. Transitioning now to working with the deepest data of the survey, the team expects to find about 40,000 galaxy clusters with about half of those being used for cosmology. They anticipate obtaining even higher precision on cosmological parameter measurements, comparable to that obtained from CMB observations. The work of eROSITA is revolutionizing cosmology at later times in the universe, and the future is exciting.

Read Astrobites’s interview with Esra Bulbul.

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This week, AAS Nova and Astrobites are attending the American Astronomical Society (AAS) summer meeting in Pasadena, CA.

AAS Nova Editors Kerry Hensley and Susanna Kohler and AAS Media Fellow Lexi Gault will join Astrobites Media Intern Niloofar Sharei and Astrobiter Lucas Brown to live-blog the meeting for all those who aren’t attending or can’t make it to all the sessions they’d like. We plan to cover all of the plenaries and press conferences, so follow along here on aasnova.org or on astrobites.org! You can also follow Astrobites on Bluesky at astrobites.bsky.social for more meeting content.

Where can you find us during the meeting? We’ll be at the Astrobites booth in the Exhibit Hall all week — stop by and say hello! You can also find Susanna, Kerry, and Lexi at the press conferences in Ballroom H Monday and Tuesday at 10:15 am and 2:15 pm PDT and Wednesday at 10:15 am PDT. AAS press conferences are open to all attendees, and they can also be found on the AAS Press Office YouTube channel for anyone not attending the meeting.

In addition to the usual press conferences, the AAS Press team has collaborated with Los Angeles’s own Griffith Observatory to arrange a special live recording of the Observatory’s acclaimed astronomy program, All Space Considered. This event is open to all AAS 248 attendees and will take place Wednesday, 17 June, at 2:15 pm PDT in Ballroom H. We hope to see you there!

Finally, you can read the currently published AAS 248 keynote speaker interviews, which were conducted by Astrobiters Niloofar Sharei, Amaya Sinha, Sowkhya Shanbhog, Katya Gozman, and Natalie Price. Be sure to check back all week as the remainder are released!

Education, Outreach, and More at AAS 248

AAS 248 features a broad range of sessions related to education and outreach. For a comprehensive and curated list of sessions, check out this post from AAS Director of Education Programs Tom Rice. Here are a few highlights (all times PDT; must be logged in to aas.org for links to work correctly); note that times and locations are subject to change:

On Monday, kick off the meeting with the Astronomy Education, Outreach, and Night-Sky Stewardship iPoster session, 9:00–10:00 am in Exhibit Hall A. Wrap up your day by attending the Reception for Astronomy Educators from 6:30 to 8:00 pm in Room 107.

Tuesday morning, hear about pressing issues relating to climate change at the Special Session What Astronomers Can Do About Climate Change: Infrastructure, Education, and Communication, from 10:00 to 11:30 am in Ballroom G. That afternoon from 2:00 to 3:30 pm, tune in to the Pathways into Modern Space Science oral session in Ballroom C.

On Wednesday, learn how to Make Your Voice Heard as an Advocate for Science in a Special Session co-sponsored by the AAS and the American Institute of Physics from 10:00 to 11:30 am in Ballroom G. Throughout the week, check in with the League of Women Voters in the Exhibit Hall — they’ll be conducting a voter registration drive during the meeting.

Thursday, the final day of the meeting, closes with a look at a local institution in the 40 Years of Community Engagement at IPAC: Lessons Learned Special Session from 2:00 to 3:30 pm in Ballroom F.

If you’re sticking around Pasadena after the meeting, consider heading to Griffith Observatory for their open house on Saturday, 20 June, 2:00–10:00 pm, which will showcase accessible observing techniques like tactile images, 3D models, live camera feeds, and sonification.

And remember, you can find a longer curated list of education-related sessions here!

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The 248th meeting of the American Astronomical Society, to be held in Pasadena, CA, 14–18 June, is nearly here. The AAS Publishing team looks forward to connecting with meeting attendees, and you can find representatives from the publishing and journals’ editorial staff at the AAS booth in the Exhibit Hall in the Pasadena Convention Center. AAS Director of Scholarly Publishing Kerry Kroffe will be available at the AAS Publishing booth, so be sure to stop by to say hello, chat about the journals, and pick up some swag!

AAS Nova Editors Kerry Hensley and Susanna Kohler, AAS Media Fellow Lexi Gault, Astrobites Media Intern Niloofar Sharei, and the rest of the Astrobites team will also be available periodically at the Astrobites booth in the Exhibit Hall. We look forward to seeing you there!

AAS Peer Review Workshop

This workshop led by the scientific editors of the AAS journals will teach participants about the peer review process, give them the opportunity to see both poor and exemplary referee reports, and provide them with hands-on experience in writing a peer review report. Participants will receive a graduation certificate. While signups for the AAS 248 peer review workshop are closed, more workshops are planned for future AAS meetings, so keep an eye out for more information about upcoming opportunities!

Open Science, Data, and AI in Astronomy: Sessions to Look for at AAS 248

Note: The links in this section take you to the corresponding entries in the AAS 248 block schedule. You must be logged in for the links to work correctly; otherwise, they will take you to the main block schedule page. Note that times and locations are subject to change.

The upcoming AAS meeting has a number of sessions, workshops, and lectures for those interested in open-source tools, data management strategies, and AI’s role in astronomy. Sunday, 14 June, will feature a trio of data-related workshops. (Note that these workshops require an additional fee and can be added to your registration.) The “Euclid Data in the Cloud: Access, Analysis, and Science Opportunities” workshop (10:00 am – 11:30 pm PDT in Room 101) will introduce participants to accessing and analyzing data from Euclid, a European Space Agency mission with NASA participation. The overlapping workshop “High Energy Science Analysis with HEASARC Services” (10:00 am – 12:00 pm PDT in Room 102), organized by the High Energy Astrophysics Science Archive Research Center (HEASARC), is targeted toward early-career scientists and anyone curious about HEASARC services. The workshop will begin with an overview of available services before transitioning into hands-on experimentation with these tools. Finally, “An Introduction to Fornax: Scalable Data and Compute for Scientific Analysis” (2:00–4:00 pm PDT in Room 101) will introduce attendees to NASA’s new Astrophysics Science Platform through live demonstrations and guided exercises.

Of particular interest regarding AI in astronomy is Monday morning’s plenary lecture from Sanmi (Oluwasanmi) Koyejo titled “The Measurement Gap: What AI Can Get Wrong and Why Astronomers Are the Fix.” This session will take place from 11:40 am to 12:30 pm PDT in Ballroom DE.

The “AI-Driven Science in the Survey Era” Special Session will take place on Tuesday, 16 June, from 2:00 pm to 3:30 pm in Ballroom F. This session will highlight recent breakthroughs in a broad range of astronomical sub-fields that have greatly benefited from the use of AI and machine-learning techniques. Also on Tuesday, check out recent work on imaging and data-handling methods at the “Observational Imaging Methods and Data Pipelines” iPoster session from 5:00 pm to 6:00 pm in the Exhibit Hall.

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Zooming through the galaxy faster than they should, hypervelocity stars are a curious population of stars whose origins are often difficult to determine. A recent study presents the first evidence of an old, low-mass hypervelocity star launched from the Milky Way’s center, providing clues into this elusive set of fast-moving stars.

Flinging Fast Stars

Image of the hypervelocity star HE 0437-5439 that was launched from the Milky Way’s core. [Illustration: NASA, ESA, and Z. Levay (STScI); Science: NASA, ESA, O. Gnedin (University of Michigan, Ann Arbor), and W. Brown (Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.)]

However, constraining a hypervelocity star’s origin to the galactic center is limited by uncertainties in distances and proper motions, muddling how well researchers have been able to trace their orbits backward. Among a number of candidate galactic center–origin hypervelocity stars, only one has been confidently identified as having been kicked from the galaxy’s center. Intriguingly, this hypervelocity star and most galactic center–origin candidates are young, massive stars — old, low-mass hypervelocity stars from the galactic center have yet to be identified.

What does this dearth of old, low-mass zooming stars mean? Either stars in the galactic center are preferentially young and massive, with fewer than expected old and small stars, or low-mass hypervelocity stars are missed by selection effects, challenging to detect in current surveys. Searching for hypervelocity stars with higher precision and sensitivity may allow astronomers to tease out this missing population and trace back more zooming stars to a Hills mechanism origin.

Discovering An Old Hypervelocity Star

Leveraging high-quality spectra from the Dark Energy Spectroscopic Instrument (DESI) survey and precise astrometry from Gaia, Shunhong Deng (University of Chinese Academy of Sciences; China West Normal University) and collaborators reported the discovery of the hypervelocity star DESI-HVS1. From the spectroscopic and astrometric analyses, the authors determined that DESI-HSV1 is a ~14-billion-year-old low-metallicity star with a mass about 80% that of the Sun’s, moving through the galaxy at 523 km/s.

Backward-integrated orbits of DESI-HVS1 for three different galactic potential models. The blue, red, and green points show the star’s current position, closest approach to the galactic center, and position 50 million years ago, respectively. Click to enlarge. [Deng et al 2026]

While more refined galaxy models and comparison to other candidate galactic center–origin hypervelocity stars are necessary to fully confirm its origins, DESI-HVS1 provides the first compelling evidence for an old, low-mass hypervelocity star candidate consistent with a galactic center launch. This suggests that the observed lack of such stars is likely not a reflection of the Milky Way’s central stellar population, but rather a consequence of observational constraints making such small hypervelocity stars particularly difficult to detect. As large spectroscopic and astrometric surveys continue to advance, the sample of galactic-center hypervelocity star candidates will grow, enabling further exploration of the stellar environment and dynamical processes at the Milky Way’s core.

Citation

“An Old, Low-mass, Metal-poor Hypervelocity Star Candidate Consistent with Galactic Center Origin,” Shunhong Deng et al 2026 ApJL 1003 L9. doi:10.3847/2041-8213/ae6505

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What’s the story behind the longest gamma-ray burst ever observed? Researchers explore how repeated interactions between a white dwarf and an intermediate-mass black hole could explain GRB 250702B’s unusual properties.

An Exceptional Gamma-Ray Burst

An image of GRB 250702B’s location within its host galaxy. [NASA, ESA, CSA, H. Sears (Rutgers). Image Processing: A. Pagan (STScI)]

These characteristics have been challenging to explain with typical models of long gamma-ray burst formation, such as collapsing massive stars, but researchers have developed numerous promising alternatives. In a new research article, astronomers have shown how GRB 250702B’s behavior might be explained by repeated close encounters between a white dwarf and an intermediate-mass black hole.

Eccentric Close Encounters

Yuri Sato (Tohoku University) and collaborators modeled the source of GRB 250702B as a white dwarf that has been captured into orbit around an intermediate-mass black hole. In their model, the white dwarf travels on an extremely eccentric orbit, drawing close to the black hole roughly once an hour. Each time the white dwarf ventures close, the black hole’s tidal forces strip away part of the star until, after about 40 such encounters, the white dwarf is completely destroyed.

Schematics showing the orbit of the white dwarf (WD; left) and the geometries that produce observable and unobservable jets. Click to enlarge. [Sato et al. 2026]

Jet Precession and Model Predictions

The discrepancy can be resolved if the angle between the jet and the black hole’s spin axis precesses over time so that only some of the jets are pointed toward us. This can occur if the accretion disk is misaligned relative to the black hole’s spin. As an alternative, disk instabilities or other processes could keep all but a few of the expected jets from being launched.

Predicted strength of the radio afterglow for the jet precession case (maximum case) and the case in which only four jets were launched due to disk instabilities or jet choking (minimum case). The x-axis shows the time since the burst was detected in X-rays by the Einstein Probe (EP). [Sato et al. 2026]

This work by Sato and collaborators demonstrates how the repeated partial tidal disruption of a white dwarf by an intermediate-mass black hole can match the properties of one of the most remarkable recent transient sources — one that has pushed astronomers to consider new ways of producing gamma-ray bursts.

Citation

“Successive Partial Disruptions with Orbital Precession in a White Dwarf–Black Hole System for Repeating GRB 250702B,” Yuri Sato et al 2026 ApJL 1003 L44. doi:10.3847/2041-8213/ae6a8f

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Dynamics of Planetary Rings Under Thermal Forces
Authors: Wen-Han Zhou et al.
First Author’s Institution: The University of Tokyo
Status: Published in ApJL

If you ask anyone what their favourite planet is, the answer you’ll most likely hear is Saturn. Why? Why else than the beautiful and intricate ring system surrounding the gas giant. The other gas and ice giants in our solar system — Jupiter, Uranus, and Neptune — have ring systems themselves but none quite as striking as Saturn’s. Would it surprise you to learn that astronomers’ best models have not yet totally explained why Saturn’s rings look the way they do?

In contrast, it may not surprise you to hear that people have been trying to explain the rings for as long as we have seen them with telescopes. We now know that planetary rings are collections of relatively small particles (think micrometre up to metre sized), most likely having once been the material of a larger body that was disrupted either by collisions or tidal forces. This material, due to the gravity of its local planet, is sculpted into a flat disc where more subtle interactions then lead to substructure forming within the disc such as gaps and ringlets. Many of these substructures are explained by well-understood physics — for example gaps being carved by embedded moonlets or resonances sculpting ring edges — though there remain some outstanding problems in our understanding.

The authors of today’s article set their sights on the problematic inner edge of Saturn’s A ring (Figure 1). They describe some mechanisms — namely the collisions of micrometeoroids within the rings — by which a sharp ring edge can be maintained, but there exists a gap in the understanding of how such an edge can form in the first place. All hope is not lost, though, as today’s authors reintroduce a physical process they call the “eclipse–Yarkovsky” effect, which seems to explain these phenomena.

Figure 1: A horizontally sliced image of Saturn’s rings shows the rich substructure and gaps within the various rings. Saturn, which is not shown here, would be to the left of the image. The authors of today’s article are particularly concerned with the bright and sharp inner (left side) edges of the A and B rings. Click to enlarge. [NASA/JPL/Space Science Institute]

Billions of Rocket-Powered Bumper Cars

The idea behind this process revolves entirely around light. When sunlight hits a particle within a planetary ring, non-absorbed sunlight imparts a little “bump” onto a particle, ever so slightly altering its trajectory. At the same time, some of the sunlight is absorbed into the particle, which heats it up; light is soon re-emitted via thermal radiation, which, again, can slightly change the trajectory of these tiny particles. From a point on the surface of each ring particle (see rightmost side of Figure 2), the photons from this thermal radiation are all emitted in random directions; however, across the whole surface of the particle there is a net force! These tiny particles are spinning, and so the side just near “sunset” is hottest and emitting the most thermal photons. In this way, the pressure from the sunlight plus the thermal radiation of each particle imparts a net torque on the ring itself which changes the angular momentum of the ring.

Figure 2: Starlight is the main source of light onto the particles that make up a planetary ring (right panel) though reflected light from the planet’s surface hits it too. This light “heats up” the ring and forms an asymmetry as the ring is eclipsed by the planet, which produces a net force. [Zhou et al. 2026]

After today’s authors detailed all of the math involved in this process (and there is a lot), they put it into practice to try to help explain Saturn’s curious rings. Including the eclipse–Yarkovsky effect together with other known effects that drive ring evolution allowed them to reproduce the optical depth profile (how thick the ring looks) of Saturn’s A ring better than ever before (notably the sharp inner edge in Figure 3). On top of this, the effect provides another avenue for moonlet formation in the outer edges of ring systems as the positive torque from the effect drives material out toward and away from the Roche limit.

Figure 3: The authors try to explain the current structure of Saturn’s A ring by initialising it with a Gaussian profile of optical thickness versus radius (black dot-dashed line) and evolving it for 81 million years under different effects. When viscous effects are included (blue dashed line), the ring spreads out, but it’s only when the eclipse–Yarkovsky (EY) effect is included (red line) that the model closely matches the observed data (grey line). [Zhou et al. 2026]

Original astrobite edited by Wasi Naqvi.

About the author, Ryan White:

I am a first-year PhD student at Macquarie University in Australia, working mainly on binary/multiple systems with massive stars (Wolf–Rayets in particular!). Outside of study, I’m probably drinking coffee, baking, reading, or going for a run. You can also find me procrastinating on Bluesky @astroryan.bsky.social.

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When the third known object from the galactic space beyond our Sun barreled through the solar system last year, Earth was in a terrible spot to view its flyby. Thankfully, however, a spacecraft that was previously busy mapping Mars took advantage of much better positioning for a closer look.

Cheap Seats

Astronomers have now observed three interstellar objects as they’ve flown through the solar system: 1I/ʻOumuamua, which shocked astronomers in 2017; 2I/Borisov, which followed in 2019 and behaved almost identically to a solar system comet; and now 3I/ATLAS, which was found buzzing toward the Sun in July 2025. As soon as 3I/ATLAS was spotted, pretty much every telescope on the planet took a look. The data swiftly revealed much that intrigued astronomers: while 3I/ATLAS was behaving essentially like a standard comet, its chemistry was nothing like its solar system counterparts, and its coma and dust outflow were strangely shaped. Among other oddities, it seemed to counterintuitively have a dust tail that pointed toward the Sun.

3I/ATLAS’s path across the sky as seen from Earth versus the clearer line of sight from Mars. The shaded region represents the times where the comet was too close to the Sun for viewing. [Xin Ren et al. 2026]

Better View from Mars

The Tianwen-1 spacecraft, which entered Martian orbit in early 2021 and has been diligently mapping the Red Planet ever since, has a high-resolution camera that’s normally pointed at the planet’s surface. By spinning the spacecraft around, a team of researchers led by Xin Ren (National Astronomical Observatories, Chinese Academy of Sciences) repurposed the camera to act as a small telescope when 3I/ATLAS flew by. In another cosmic coincidence, 3I/ATLAS happened to pass very near Mars last fall, and this close approach gave Tianwen-1 a great out-of-plane view of the coma. The orbiter managed to capture 57 images of 3I/ATLAS over three days last fall, representing China’s first-ever observations of an object from an asset in deep space.

Stacked images of 3I/ATLAS from the Tianwen-1 orbiter across three epochs; the tail’s apparent shape shifts as the viewing geometry changes. Click to enlarge. [Xin Ren et al. 2026]

As new surveys begin to turn up interstellar interlopers more often, this improvised observation makes a tidy point: the spacecraft already scattered across the solar system can double as a fleet of opportunistic comet-watchers, each offering a view we simply can’t get from home.

Citation

“Interstellar Object 3I/ATLAS Observed from Mars by China’s Tianwen-1 Spacecraft,” Xin Ren et al 2026 ApJL 1003 L10. doi:10.3847/2041-8213/ae61b3

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Planets that get too close to their host stars are liable to be engulfed and consumed. New research explores how to identify stars that have had a planetary snack.

It’s Snack Time

Being a planet that closely orbits its star is dangerous, and various dynamical processes can draw a planet inward past the point of no return. When a planet vanishes beneath the surface of its host, it eventually disintegrates within the star, its atoms mixing into the blazing stellar soup.

This outcome is likely extremely common across the universe, and researchers have begun to see evidence for it: stars that appear to have absorbed angular momentum from their planets, white dwarfs with uncanny metals in their spectra, and stars with chemical abundances that don’t match those of their siblings. Now, in a recent publication led by Kaitlyn Lane (Vanderbilt University), researchers seek to find observational signatures of planetary engulfment of rocky exoplanets by main-sequence stars.

Modeling Engulfment

Lane’s team focused on main-sequence stars in the range of 0.5 to 1.4 solar masses, using one-dimensional analytical models to determine which of these stars will most readily display signs of having engulfed a planet. They simulated the stars as they consumed either an Earth-like planet or a super-Earth with the same composition as Earth but 15 times its mass.

Diagram showing a planet being engulfed by its star and beginning to disintegrate before migrating inward. The boundary between the star’s outer convective zone (CZ) and inner radiative zone is shown. Click to enlarge. [Lane et al. 2026]

After that relatively lengthy phase, the process proceeds rapidly: as the planet inches deeper into its star, the drag forces grow stronger and the planet’s demise accelerates, with the planet disintegrating over the course of hours. In the last phase, the planet makes its final plunge and is destroyed in a half hour.

Signs of Planets Past

Lane’s team found that the planets tended to be destroyed fully within the outer convective layer of their stars, except in the case of the most massive stars studied here. For more massive stars, the outer convective zone is shallower than it is for the less massive stars, allowing a chunk of each planet to survive the passage through the convective zone to reach the radiative zone below.

The trajectories of three example cases, showing how the planet loses mass as it spirals inward. In the 1.4-solar-mass case, part of the planet survives to reach the radiative zone, but the shallowness of the star’s convective zone means that the disintegrated planetary material is easier to observe. Click to enlarge. [Lane et al. 2026]

While the authors acknowledge that there’s more work to be done — they plan to investigate the impacts of planetary engulfment on stellar structure more closely, for example — this work represents an important foray into identifying targets for future studies of stars that have eaten their planets.

Citation

“Observable Metal Pollution in Main-Sequence Stars: Simulations of Rocky Planets Engulfed by Stars in the 0.5 to 1.4 M_⊙ Range,” Kaitlyn T. Lane et al 2026 ApJ 1003 67. doi:10.3847/1538-4357/ae5b9a

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: A Panchromatic JWST Spectrum of a Giant Starspot on the Fully Convective M Dwarf TOI-3884
Authors: C. A. Murray et al.
First Author’s Institution: University of Colorado Boulder
Status: Published in ApJ

We often picture stars as smooth, glowing spheres, as if they’ve been run through an Instagram filter. But real stars have spots: cooler, darker regions on a star’s surface caused by strong magnetic fields.

Annoyingly, these spots can seriously interfere with how we study exoplanet atmospheres.

How to Probe a Planetary Atmosphere

Planetary atmospheres are often probed through transmission spectroscopy. When a planet transits its star, some starlight passes through the planet’s atmosphere before reaching us. We can distinguish the light that has passed through the planet’s atmosphere by comparing the star’s light in transit versus out of transit. In doing so, we can isolate the atmospheric spectrum and look for absorption features of species like water or oxygen.

Easy, right?

How Starspots Get in the Way

Things get more complicated once we stop thinking of the star as if it’s been smoothed out by an Instagram filter. Starspots are cooler than the surrounding stellar surface, which means they emit a different spectrum. They are also constantly changing: new spots can form, old ones can disappear, and the star’s rotation carries them in and out of view. This changes things.

First of all, your star’s spectrum changes over time, which could mean that the star’s spectrum out of transit is not the same as the star’s spectrum during transit. On the other hand, the planet may transit across a starspot instead of a “normal” stellar region. In this case, the light we measure during the transit is affected by the spot, and it is no longer accurate to directly compare it with the overall stellar light outside the transit.

Ultimately, absorption features that we thought were from the planetary atmosphere could actually be coming from starspot contamination instead.

Starspot Models: Our Solution?

To deal with this, astronomers build starspot models, where they vary the spots in terms of the following:

• The surface covering fraction: this parameter tells us how much of the stellar surface is covered in spots
• The temperature contrast: this parameter tells us how much cooler (in ratio) the spot is compared to the rest of the stellar surface, and by proxy how much dimmer

These models are promising, but how do we know that we have chosen the right parameters?

A Unique Laboratory: TOI-3884

The TOI-3884 system is a unique laboratory for testing our starspot models. As seen in Figure 1, it has very convenient starspot geometry, with a large starspot located close to its pole. On top of that, we observe this star almost completely pole-on, which means that we always see this starspot, no matter how much the star rotates. To top this all off, the star hosts a close-in planet, which orbits the star from pole to pole.

Figure 1: Illustration of the TOI-3884 system. The pole (and rotation axis) of the star is indicated with a black “x,” indicating that we see the star almost pole-on. The polar starspot is indicated in grey, and the transiting planet TOI-3884b is indicated in black. Different dates are shown, illustrating how the system evolves over the span of a few weeks. [Adapted from Mori et al. 2025]

So… How Good Are Our Models?

From the JWST observations, the authors extract a starspot spectrum for the first time. Figure 2 shows this as the spot contrast (how much dimmer the spot is than the surrounding stellar surface) plotted across different wavelengths. To see how well our models are doing, they compare this observed spectrum to two commonly used starspot models. The difference between the data and the models (the residual) is plotted in the lower panel.

Figure 2: The spectrum of TOI-3884’s starspot. The y-axis in the upper panel, the spot contrast, indicates how much dimmer the starspot is compared to the “normal” stellar surface. Different observations taken with JWST are indicated in different colored crosses, and other previous observations are overplotted in various other shapes. Model starspot spectra are shown in dashed or dotted black lines. The residuals between the model spectra and the JWST observations are shown in the bottom panel. [Adapted from Murray et al. 2026]

There’s still work to be done before we can confidently probe planetary atmospheres at optical wavelengths without worrying about stellar contamination, and this observed starspot spectrum provides a unique benchmark to test future starspot models. For now, the near-infrared remains a safer and more reliable window for planet atmosphere studies.

Original astrobite edited by Natalie Price.

About the author, Elise Koo:

I’m a PhD student at the University of Amsterdam, working to detect magnetic interactions between stars and their planets using radio and spectroscopic observations. Outside of research, I like to try out a variety of sports.

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The Antennae galaxies are a nearby pair of interacting galaxies, shown in optical light from the Hubble Space Telescope (left) and in infrared light from JWST (right) in the image above. Between the two galaxies’ bright nuclei, there is a vast and dusty molecular cloud complex that harbors a large number of massive young star clusters — and in a recent article led by Rupali Chandar (University of Toledo), researchers have worked to pin down exactly how many clusters are embedded within the dusty whorls of the Antennae galaxies. The team used JWST to search for emission from star clusters too thickly blanketed with dust to be visible in previous observations by Hubble. They ultimately identified 45 sources, 40 of which were seen for the first time in this study. These star clusters mostly inhabit the overlap region between the two galaxies, are less than 2.5 million years old, and each contain roughly 10⁴–10⁶ solar masses. To learn more about how JWST’s infrared capabilities unveiled young star clusters in these interacting galaxies, be sure to check out the full article linked below.

Citation

“Nowhere Left to Hide: Uncovering All of the Massive Young Embedded Star Clusters in the Antennae with JWST,” Rupali Chandar et al 2026 ApJ 1002 64. doi:10.3847/1538-4357/ae56e8

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The fastest spinning pulsars in the universe are often quite difficult to detect. Leveraging multiple observations from the largest single-dish telescope in the world, researchers have discovered six previously undetected pulsars.

Millisecond Pulsars in Globular Clusters

Globular clusters, compact collections of tens of thousands to millions of stars, are highly dense and rife with dynamical interactions. These active environments are ideal factories for the formation of millisecond pulsars — the extremely fast-spinning cores of once-massive stars, shining beams of radio emission from their poles. One way millisecond pulsars are thought to form is when a pulsar in a binary system steals mass from its companion star, transferring angular momentum and causing the pulsar to spin up. The densely packed environment in a globular cluster provides ample opportunity for a pulsar to acquire a companion to siphon.

However, millisecond pulsars in distant globular clusters are notoriously difficult to detect. Traditional pulsar searches that rely on a single observation tend to miss millisecond pulsars, many of which have signals too faint to be distinguished from noise or radio interference. Instead, researchers must rely on a different method to find these fast-spinning pulsars.

FAST, the 500-meter single-dish radio telescope located in southwestern China. [Wikipedia user SCJiang; CC BY 4.0]

Stack Search Success

To find faint millisecond pulsars, researchers have developed the stack search method, in which multiple radio observations are combined to tease out faint signals and decrease noise. Reliably stacking observations across epochs requires stability; isolated millisecond pulsars, now no longer spinning up after losing their companion, have very stable rotation periods, making them ideal targets for the stack search method. To date, the stack search method has successfully identified nine isolated globular cluster millisecond pulsars using data from the Arecibo, Parkes, and Green Bank radio telescopes.

Power spectra from a discovered millisecond pulsar M15N. The black solid lines show the 19 individual observations of the pulsar, and the red solid line in the top panel shows the stacked spectrum. The stack search method pulls out a clear pulsar signal. [Dai et al. 2026]

While previous studies identified brighter pulsars in the targeted globular clusters, the authors confirmed that all six newly discovered pulsars are too weak to be reliably recovered from single-epoch searches, underscoring the importance of the stack search method. In particular, this search increased the known pulsar populations of NGC 6517 and M15 by 27% and 18%, respectively, suggesting that a meaningful fraction of globular cluster pulsars are easily missed in traditional pulsar searches. Future studies employing this stack search method will continue to detect faint millisecond pulsars, unlocking this elusive population for further exploration.

Citation

“The Stack Search Tests on FAST Data: Discovery of Six Faint Isolated Millisecond Pulsars in NGC 6517 and NGC 7078 (M15),” Yinfeng Dai et al 2026 ApJL 1002 L31. doi:10.3847/2041-8213/ae5dbb

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Where do black hole mergers happen? Recent research finds evidence that most black hole mergers occur in triple systems containing a close inner binary and a more distant third party.

Assembling Merging Black Holes

Thanks to the combined efforts of the LIGO, Virgo, and KAGRA gravitational wave detectors, we’ve now collected the subtle signals from several hundred pairs of merging stellar-mass black holes. As this collection of spacetime ripples continues to grow, researchers are seeking to understand how these merging black hole pairs were assembled.

In the simplest scenario, pairs of high-mass stars independently evolve into black holes, lose momentum by emitting gravitational waves, and meld into one another. But the population of merging black holes likely contains contributions from multiple sources, including multiple-star systems, the disks surrounding accreting supermassive black holes, and black holes that have already experienced a merger. Which of these merging populations is reflected in our catalog of gravitational wave events?

Modeling Challenges

A black hole binary system with aligned spins and orbit (top) and a binary with spins tilted by 90 degrees (bottom). [AAS Nova/Kerry Hensley]

So far, the increasingly large pool of gravitational wave detections tentatively points to a feature that could illuminate the sites of black hole mergers: a peak in the spin–orbit tilt distribution around 90 degrees. This feature has been most confidently extracted from nonparametric analyses, which do not make assumptions about the population of merging black holes, but it has also been hinted at in parametric analyses, which do make population-level assumptions.

Triple-System Feature

To investigate this feature further, a team led by Jakob Stegmann (Max Planck Institute for Astrophysics) performed a new, astrophysically motivated parametric analysis of the most recent catalog of gravitational wave detections from LIGO, Virgo, and KAGRA.

The three populations in the team’s modeling. [Stegmann et al. 2026]

Posterior predictive distribution of black hole spin–orbit tilts. Both the authors’ modeling (solid blue line) and the nonparametric modeling performed by the LIGO–Virgo–KAGRA collaboration (solid green line) find evidence for a peak in the spin–orbit tilt distribution near cosθ = 0. [Adapted from Stegmann et al. 2026]

Stegmann and collaborators pointed out that the triple-system scenario aligns well with other properties of the observed population of black hole mergers, such as the mass and effective spin distributions. This scenario may also be necessary to explain certain merging pairs that might have had slightly eccentric orbits at the moment of merging. If future gravitational wave observations strengthen the evidence for a peak in the spin–orbit tilt distribution near 90 degrees, it will have profound implications for how and where black holes merge in our universe.

Citation

“Gravitational-Wave Observations Suggest Most Black Hole Mergers Form in Triples,” Jakob Stegmann et al 2026 ApJL 1000 L59. doi:10.3847/2041-8213/ae52ec

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Retrieving the Red Edge on Earth-Like Planets with Heterogeneous Clouds and Surfaces
Authors: Zachary Burr et al.
First Author’s Institution: Jet Propulsion Laboratory; ETH Zurich
Status: Published in ApJ

In the next 25 years, astronomers could find signs of life on other planets with the launch of the Habitable Worlds Observatory. Atmospheric signs of life, known as atmospheric biosignatures, are how astronomers currently search for life on other planets. Figure 1 shows examples of atmospheric biosignatures with pictures of each chemical’s origin on Earth. Before E.T. can phone home, though, we have to understand what chemicals make up a planet’s atmosphere. To do this, astronomers can use spectroscopy to observe a planet’s atmosphere in different wavelengths and measure the types and quantities of chemicals present.

Figure 1: Atmospheric biosignatures present in Earth’s atmosphere. More abundant biosignatures include oxygen and ozone (byproducts of photosynthesis in plants and bacteria) and nitrous oxide (byproduct of bacteria that don’t need oxygen to survive). Less abundant biosignatures include isoprene (released from the breakdown of leaves that have fallen from trees) and sulfur gases (byproducts of cyanobacteria). [Kaz Gary]

But are atmospheric biosignatures the only way to tell if life exists on other planets? Short answer: absolutely not. Let’s take Earth as an example. If we imagine Earth as a directly imaged exoplanet and take spectra of the light it reflects, you’ll find that around near-infrared wavelengths (~700 nanometers or just past the red part of the visible light spectrum), the light reflected off of Earth increases sharply. This sharp increase is called the vegetation red edge and is caused by plant and ocean life on Earth’s surface as shown in Figure 2. This is made possible because chlorophyll (the thing that makes plants green) absorbs nearly all visible light but reflects near-infrared light. The vegetation red edge is an example of a surface biosignature. In today’s article, the authors determine if the vegetation red edge will be visible in spectra of Earth-like exoplanets!

Figure 2: Spectra of different sources of the vegetation red edge on Earth. The vegetation red edge is highlighted in gray where the spectra rapidly increase and then level off beyond the visible light part of the spectrum. Each color represents a different source with pictures of each source on the right-hand side of the plot. [O’Malley-James and Kaltenegger 2019]

Snapshots

Planets rotate; that’s how we have morning, noon, and night in 24 hours guaranteed. This means that different parts of the surface will be visible at different times when we take spectra. Sometimes, we may see more ocean than land, other times not. To determine if the vegetation red edge would be visible at all points in Earth’s day, the authors simulated nine different spectra of modern-day Earth representing nine snapshots of Earth’s rotation. Additionally, they also simulated a time-averaged spectrum that shows an entire Earth day in one snapshot without the time variability. These spectra are shown in Figure 3.

Figure 3: Spectra of a directly imaged modern-day Earth at nine different times in its rotation. The y-axis is the ratio of the planet’s signal to the star’s signal and the x-axis is wavelength in microns. Each color represents a time in UTC and the black curve represents the time-averaged spectrum. [Burr et al. 2026]

Arr! There Be… Vegetables?

After running the models, the authors were able to detect a sharp increase in the surface albedo value in every spectrum, including the time-averaged one. This result is shown in Figure 4. The authors take this result one step further in order to validate that the vegetation red edge is actually a result of surface variation of vegetation. They re-run models on each of their spectra but instead include a constant surface albedo instead of a time-varying one. This resulted in incorrectly measured radii, chemicals, and surface gravity in nearly all of the models. Without the vegetation red edge and surface features, the models could not accurately determine if life was present on Earth.

Figure 4: Retrieved surface albedos for the nine time-varying spectra. The surface albedo is broken down into three different values (a₁, a₂, a₃). Each of these values represents a change in the surface albedo at different wavelengths (i.e., how reflective the surface is at three different wavelengths). The nine spectra were broken down by the amount of surface that was visible at that time and color-coded for each category. The time-averaged spectrum is shown in gray. Each category of spectra was able to retrieve an increase in reflected light from the surface at vegetation red edge wavelengths. The spectra that had the majority land visible have the biggest increase in the surface albedo. This makes sense since the amount of visible vegetation is the largest with majority-land planets. [Burr et al. 2026]

Original astrobite edited by Madison VanWyngarden.

About the author, Kaz Gary:

I am a fourth-year PhD candidate at The Ohio State University with a passion for planets. My current work focuses on modeling exoplanet observations for the Habitable Worlds Observatory and understanding planetary atmospheres. Outside of research, I help develop planetarium shows and love all forms of science communication. In my free time, I enjoy playing tabletop RPGs, painting, watching terrible reality TV, and hanging out with my pet hedgehog.

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Each Jupiter-size planet in the galaxy falls into one of three distinct categories: hot, warm, or cold. A new study suggests that despite the apparent differences between these populations, they may have all formed from the same underlying dynamical process: a game of pool played at planetary scales.

A Diversity of Jupiters

Though our solar system has only one Jupiter-size planet, elsewhere in the galaxy we have found three different species of these massive gas giants. Cold Jupiters closely resemble their namesake and orbit far from their host stars; hot Jupiters are the opposite and are found whipping around their stars on extremely close-in orbits. In between these are the warm Jupiters, which tend to orbit in the intermediate space between 0.1 and 1.0 au.

An artist’s depiction of a hot Jupiter. These planets orbit extremely close to their host stars, but likely got to their locations by scattering inward from more distant orbits. [NASA/JPL-Caltech]

Given these differences, it’s often thought that each of these populations arrived at its current location through different dynamical processes and that the history of the warm Jupiters is likely quite different from the history of the hot Jupiters. However, a new study led by Julia Esposito (Georgia Institute of Technology) has proposed an alternative view. Maybe these populations, though they appear different now, were all created by the same process: planet–planet scattering.

Virtual Planetary Billiards

A schematic showing where different planets ended up as a function of where they scattered from during their evolution. Click to enlarge. [Esposito et al. 2026]

At the end of the simulation, the team surveyed the digital carnage. Almost every virtual system ended with only two planets after either ejecting one away from the star or having two planets collide. But, remarkably, the remaining two-planet systems looked tantalizingly similar to what we actually observe, with a mix of hot, warm, and cold Jupiters. Even more exciting, the end populations were highly correlated to where the violent scattering event took place.

For example, the warm Jupiters were almost all produced by “warm scattering” simulations, where the scattering took place between 0.1 and 1.0 au. The planets that survived the simulations and ended up as warm Jupiters matched all of the properties of the real warm Jupiter population: they had nearby companions, were moderately eccentric, and were mostly aligned with their stars. The hot Jupiters, meanwhile, were almost all produced by “cold scattering” events where the flybys happened far from the star and resulted in one planet hurtling inwards. These also matched all of the observed properties of real hot Jupiters.

The researchers concluded that planet–planet scattering can produce both the warm and hot Jupiter populations so long as you let the planets scatter from a variety of different distances. This exciting theoretical insight, if correct, would mean that astronomers could stop searching for different pathways to create each population. Happily, this model also provides testable predictions, and the authors lay out how the theory could be supported or disproven with additional data. Through virtual experiments like these, astronomers continue to build up an understanding of how the wide range of planetary architectures observed across the galaxy came to be.

Citation

“Unified Formation Channel of Hot and Warm Jupiters via Planet–Planet Scattering,” Julia Esposito et al 2026 ApJL 1003 L3. doi:10.3847/2041-8213/ae61b0

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Discovered in December 2024, the roughly 60-meter-wide asteroid 2024 YR4 was initially thought to have a slim chance of striking Earth in 2032. Further observations ruled out an Earth impact but left open the possibility of a Moon impact. New JWST observations show that 2024 YR4 will speed past both Earth and the Moon without a collision.

Another Update on 2024 YR4

In April 2025, we featured a Research Note that described March 2025 JWST observations of 2024 YR4 and characterized the asteroid’s size and albedo. At the close of that article, the authors suggested that further JWST observations in early 2026 could help to refine our understanding of the asteroid’s trajectory and determine whether it would strike the Moon.

On 18 and 26 February 2026, JWST carried out those critical observations. In this dataset, the asteroid is bright enough to be detected confidently, and the background is peppered with a sufficient number of reference stars — two factors necessary to determine the precise track of the asteroid as it zipped through space.

Trajectory Refinement

Difference between the position of 2024 YR4 determined in this work using three different reduction methods (red, blue, and green circles) and the position drawn from the existing orbit from the JPL Horizons database. The different analysis methods yielded consistent results. [Adapted from De Wit et al. 2026]

Combining the latest JWST observations with existing data stretching back to the asteroid’s discovery, de Wit and coauthors determined a new, highly precise orbit for the object — one that definitively shows that the asteroid will safely pass by the Moon at a distance of 22,900 ± 800 km in 2032. In addition to ruling out the upcoming lunar impact, the team also ruled out any collisions with Earth in the next 100 years. Phew!

Position of 2024 YR4 as seen by JWST in February 2026 (white dashed circle) compared to the asteroid’s location estimated from existing data (red circle). [De Wit et al. 2026]

High-Impact Science

This work highlights JWST’s potential as a tool for planetary defense. The February 2026 observations detailed here represent the faintest-ever detection of a near-Earth object, and JWST can detect objects far fainter than ground-based telescopes can. This ability allows JWST to observe potentially hazardous asteroids over a larger swath of their orbits, which translates to earlier trajectory estimation — JWST pinned down 2024 YR4’s orbit two years before the asteroid would have become bright enough for ground-based telescopes to do so.

JWST’s role may be even more important for smaller objects that rapidly become undetectable after discovery. De Wit’s team demonstrated this for a 10-meter-diameter 2024 YR4 clone on the same trajectory; for an object of this size, JWST would be able to rule out an Earth impact before the asteroid became undetectable, but ground-based telescopes could not. With surveys from facilities like Vera C. Rubin Observatory and Near-Earth Object Surveyor set to discover hundreds of thousands of new near-Earth objects, JWST’s role as a hazard assessor will likely be in high demand.

Citation

“JWST Observations of Asteroid 2024 YR4 Rule Out a 2032 Lunar Impact and Demonstrate a New Regime for Planetary Defense Follow-Up,” Julien de Wit et al 2026 ApJL 1003 L21. doi:10.3847/2041-8213/ae6a95

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: Shocks, Winds, and a Torus: The Large Binocular Telescope Interferometer (LBTI) Resolves the Active Nucleus of NGC 4151
Authors: Jacob W. Isbell et al.
First Author’s Institution: University of Arizona
Status: Published in ApJ

At the centre of nearly every galaxy lies a supermassive black hole that dominates this innermost region. Not only is there this millions-of-solar-masses dark beast, but usually too a whole bunch of stuff — stars, gas, dust, and more — which is often quite bright! When there is plenty of this material quite close to the black hole, we believe physics takes control to flatten it into a family of disk and toroidal structures in what we call the unified model of active galactic nuclei (AGNs; see Figure 1).

Figure 1: The unified model of AGNs asserts that there is an inner accretion disk, surrounded by a dusty torus that cohabitates with clouds moving at different velocities (the so-called broad and narrow line regions), and sometimes even relativistic jets extending from the accretion disk to galactic scales; you can read more about AGN structure in this Astrobites guide. [Emma Alexander; CC BY 4.0]

The cores of AGNs are often imaged at the smallest scales (e.g., their accretion disks, viewed with interferometers like the Very Large Telescope Interferometer) and the largest scales (e.g., their relativistic jets, viewed with radio interferometers), but comparatively less effort has gone to directly observing the predicted dusty tori in the mid-infrared. That is exactly what today’s authors set out to do using the Large Binocular Telescope Interferometer (LBTI) — a pair of 8.4-metre-aperture mirrors separated by just over 14 metres and combined to simulate a telescope effectively 29 metres wide. This lets astronomers take direct images at a much higher resolution than a smaller-aperture telescope, and hence directly peer into the region around AGNs where this dusty torus should lie.

Today’s authors turn the LBTI towards NGC 4151, a medium-luminosity AGN. With the large effective aperture of the LBTI, they were able to resolve scales in the AGN region as small as 4.4–9.1 pc, about 14–30 light-years depending on the wavelength (see Figure 2), in the mid-infrared. These observations revealed warm dust emission in a complex structure around the central supermassive black hole. The authors note a central bar at all wavelengths, with a significant extension of cool dust arcing to the west (right in the image) and warmer dust localised to the centre (as evident by 3.7- and 4.8-micron emission only nearest to the supermassive black hole and its accretion disk).

Figure 2: The deconvolved images of the AGN core of NGC 4151 show a very bright central source (the innermost region around the supermassive black hole), as well as some complex surrounding structure particularly at long wavelengths. The interpreted morphology is described in Figure 3. These images are deconvolved, meaning that known optical effects are corrected for on the raw data to produce a sharper image. [Adapted from Isbell et al. 2026]

Figure 3: Three interpretations of the observed morphology are presented by the authors. The left panel illustrates the different regions surrounding the supermassive black hole (together with the results of other studies cited in the article). The right panel shows the suggested interpretations explaining the morphology. [Isbell et al. 2026]

The second interpretation aligns with a different version of the unified model: one in which a geometrically thin disk replaces a thick torus around the AGN core. Provided the disk is optically thin too, the authors favour this approach as it is consistent with the geometry of ionised emission that worked against the first interpretation. While other studies suggest that this thin disk should be optically thick, this morphology is at least better aligned with what we see in other AGNs.

The third interpretation suggests that the emission comes from only the radiation pressure–driven wind emanating from the AGN core. The authors disfavour this explanation, citing previous radiative transfer simulations that show that the flux should fall off with distance from the core too quickly to be consistent with the observations.

No matter the interpretation, these LBTI observations are an important glimpse into the future of mid-infrared AGN studies that will be done with 30-metre-class telescopes (such as the European Southern Observatory’s Extremely Large Telescope). This article, together with the group’s similar study on NGC 1068, is challenging and refining an accepted view of AGN morphology — the consequences of which apply to galaxies near and far — and poses new questions perfect for sophisticated hydrodynamic and radiative simulations.

Original astrobite edited by Margaret Verrico.

About the author, Ryan White:

I am a first-year PhD student at Macquarie University in Australia, working mainly on binary/multiple systems with massive stars (Wolf–Rayets in particular!). Outside of study, I’m probably drinking coffee, baking, reading, or going for a run. You can also find me procrastinating on Bluesky @astroryan.bsky.social.

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The outer solar system is inhabited by swarms of small objects that are challenging to observe and characterize. When one of these objects travels in front of a star, from our perspective, the passage provides a brief chance to study these distant, icy denizens of our solar system. In a recent article, Estela Fernández-Valenzuela (University of Central Florida) and coauthors described how they predicted and observed stellar crossings by Weywot, the largest moon of the dwarf planet Quaoar, which lies roughly 44 au from the Sun. In the image above, the black dashed lines indicate the areas where Weywot was predicted to briefly blot out the light from a star, and the blue lines show the updated regions based on Hubble Space Telescope observations. In each panel, the green squares and red circles show where the occultation was and was not detected, respectively. There were five successful detections of Weywot’s passage across a star, allowing the team to constrain Weywot’s diameter to 116–172 km. The team also found that Weywot is much darker than the body it orbits, which has important implications for how the system formed. To learn more about the planning process for and results of these observations, be sure to check out the full research article linked below.

Citation

“Weywot, an Unusually Low-Albedo Satellite in the Trans-Neptunian Region,” Estela Fernández-Valenzuela et al 2026 ApJL 1002 L37. doi:10.3847/2041-8213/ae6076

The post Featured Image: Chasing Weywot’s Shadow appeared first on AAS Nova.

How do massive galaxies form and evolve? A recent study traces the stellar and dust distributions across evolutionary phases of massive galaxies to better understand how massive dusty star-forming galaxies fit into the picture.

Dusty Massive Galaxies

Massive galaxies, like the Milky Way or even larger, undergo phases of active star formation and quiescent phases of inactivity, but exactly how these galaxies evolve through these stages is not yet fully understood. Dusty star-forming galaxies, which are undergoing a period of intense star formation and shrouded in dust, might be the missing evolutionary step between star-forming and quiescent phases of massive galaxy evolution. 

Currently, the leading explanation for massive galaxy formation and evolution is inside-out growth — star formation and quenching start in the inner regions of a galaxy and progress outward. However, it’s not clear whether dusty star-forming galaxies also follow the favored inside-out pathway, or if they instead proceed outside-in, first growing their disks and then assembling a central bulge.

Example of JWST NIRCam images with ALMA contour lines overlaid for select dusty star-forming galaxies in the sample. [Modified from Bodansky et al 2026]

Multiwavelength Morphological Comparisons

To directly compare the star and dust morphologies across massive galaxies, Sarah Bodansky (University of Massachusetts, Amherst) and collaborators selected a sample of 33 dusty star-forming galaxies from the GOODS-ALMA 2.0 survey that searched the sky for 1.1-mm dust emission as well as star-forming and quiescent comparison samples drawn from JWST observations. Combining the ALMA survey data with JWST imaging, the authors studied the rest-frame optical (stars) and rest-frame near-infrared (dust) morphologies of dusty, star-forming, and quiescent galaxies at redshifts around cosmic noon (a few billion years after the Big Bang).

When comparing optical morphologies, the authors found that dusty star-forming galaxies and typical star-forming galaxies had similar distributions, but their near-infrared morphologies showed clear differences. Dusty galaxies tended to show more compact near-infrared emission, with dust tracing their stellar populations and more concentrated in the galaxies’ central regions. Though clearly different from star-forming galaxies, the authors noted striking similarities between the near-infrared morphologies of the dusty star-forming and quiescent galaxies, especially within their centers.

Average surface brightness profiles for the rest-optical (left) and rest-near-infrared (right) for the dusty (black), star-forming (blue), and quiescent (red) galaxies. In the near-infrared, the dusty star-forming galaxy profile appears very similar to the quiescent galaxy profile. [Bodansky et al 2026]

Citation

“JWST+ALMA Reveal the Buildup of Stellar Mass in the Cores of Dusty Star-forming Galaxies at Cosmic Noon,” Sarah Bodansky et al 2026 ApJ 1001 235. doi:10.3847/1538-4357/ae4f64

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The NSF–DOE Vera C. Rubin Observatory has yet to begin its 10-year Legacy Survey of Space and Time, but it’s already keeping an eye on the sky. Astronomers recently described Rubin’s serendipitous spotting of 3I/ATLAS days before the interstellar object’s discovery.

Interstellar comet 3I/ATLAS as seen by the Hubble Space Telescope on 30 November 2025. [NASA, ESA, STScI, D. Jewitt (UCLA), M.-T. Hui (Shanghai Astronomical Observatory). Image Processing: J. DePasquale (STScI)]

Welcome, 3I/ATLAS

Our solar system has been playing host to a rare interstellar tourist: 3I/ATLAS. Just the third known interstellar object to have passed through our star system, 3I/ATLAS was discovered on 1 July 2025 by the robotic telescope network of the Asteroid Terrestrial-impact Last Alert System (ATLAS). After making its closest approach to the Sun in October 2025, 3I/ATLAS is now journeying out of the solar system and is currently located beyond the orbit of Jupiter.

While astronomers would likely grumble about hosting a human guest for nearly a year, they’ve been thrilled with 3I/ATLAS’s lengthy visit and have turned countless telescopes toward the rare interstellar object. They’ve also turned to the archives, searching for pre-discovery sightings of the object — and finding them in the commissioning data from one of the most highly anticipated observatories on the planet: Rubin Observatory.

A Serendipitous Sight

3I/ATLAS as seen by Rubin Observatory on 3 July 2025. [Chandler et al. 2026]

For most of 2025, Rubin was in its commissioning phase, carrying out science validation observations — a critical period during which instruments, procedures, and pipelines are fine tuned, and the quality and quantity of data collection can vary. On 20 June 2025, the very first night of its science validation survey, Rubin happened to turn toward the small patch of sky containing the as-yet undiscovered 3I/ATLAS.

More to Come

In a recent article, Colin Orion Chandler (LSST Interdisciplinary Network for Collaboration and Computing Frameworks; University of Washington) and collaborators described how they tracked down 3I/ATLAS in Rubin’s commissioning data after the object’s discovery was announced. In total, the observatory serendipitously spotted 3I/ATLAS nine times between 21 June and 2 July, then several more times — some on purpose, some by chance — between 3 and 20 July.

Serendipitous observations of 3I/ATLAS by Rubin. [Chandler et al. 2026]

In their analysis of Rubin’s observations of 3I/ATLAS, Chandler and collaborators found that had the science validation survey started sooner, and had the analysis pipelines been operational, Rubin might have been the first to welcome humanity’s third interstellar visitor. Findings like these heighten the anticipation for the start of the Legacy Survey of Space and Time, during which Rubin will surely build upon its already impressive record of interstellar object observations.

Citation

“NSF-DOE Vera C. Rubin Observatory Observations of Interstellar Comet 3I/ATLAS (C/2025 N1),” Colin Orion Chandler et al 2026 ApJL 1001 L35. doi:10.3847/2041-8213/ae4b3a

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Editor’s Note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org.

Title: A Deep Search for Exomoons Around WISE 0855 with JWST
Authors: Mikayla J. Wilson et al.
First Author’s Institution: University of California, Santa Cruz
Status: Published in AJ