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M33

Galaxies pull in and pump out gas as they form and evolve, but distinguishing between the two directions is tricky. A recent study used emission lines and dust absorption to try to pin it down.

Inflow or Outflow?

Throughout their lives, galaxies churn gas into stars, stars fuse new metals, supernovae blow enriched material back out, and the cycle repeats. To maintain this process and sustain star formation, a galaxy must fuel up by accreting gas from its surroundings. However, catching galactic gas accretion has proven difficult — both emission from gas falling into the galaxy (inflows) and gas blown out by supernovae (outflows) can appear blueshifted or redshifted along an observer’s sight line, depending on if the flowing material is in front of or behind the galaxy.

While direct evidence of inflows has been identified in the Milky Way, only a few direct detections of inflowing gas in other galaxies exist due to the degeneracy of inflow and outflow emission-line features. Relying on additional absorption measurements, some studies have teased out inflows in other galaxies, but these star formation fuel pumps remain overwhelmingly evasive. The angle at which we observe a galaxy also limits our ability to detect both inflows and outflows, with face-on galaxies best oriented to detect these shifted spectral features. How then do we uncover this critical component of a galaxy’s evolution?

Breaking Through with the Balmer Decrement

Balmer decrement diagram

A diagram illustrating the degeneracy in emission spectra of galaxies, with the top panel showing an inflowing component and the bottom panel showing an outflowing component. While the Hα emission is similar, the Hβ emission is more affected by extinction due to dust in the galaxy’s disk, making it possible to identify inflow versus outflow based on the Balmer decrement. Click to enlarge. [Sitaram et al 2026]

To try to break through the confusion between inflows and outflows, Meghna Sitaram (Columbia University) and collaborators explored how the strengths of hydrogen emission lines vary depending on the location of the emitting gas. Referred to as the Balmer decrement, the ratio between the Hα (redder) and Hꞵ (bluer) emission lines is sensitive to dust between the emitting gas and the observer. Because dust preferentially absorbs bluer photons, an inflow or outflow behind a galaxy is expected to have a higher Hα/Hꞵ ratio due to the intervening dust in the galaxy’s disk absorbing some of the Hꞵ emission.

Testing this idea, the authors performed a hydrodynamic simulation of an isolated, face-on Milky Way–like galaxy and tracked inflows and outflows over a billion years. From the simulation, they extracted mock spectral observations to measure the ionized gas motions and Hα and Hꞵ emission lines along different sight lines throughout the galaxy. Separating gas components into three categories — inflow, outflow, and in the disk — the authors found that dust extinction does cause noticeable differences in the Balmer decrement depending on a component’s location with respect to the disk.

histograms

The distribution of Balmer ratios between different components in the interstellar medium and in front of the galaxy (left) and behind the galaxy (right). Material in front of the galaxy shows lower Hα/Hβ ratios. Click to enlarge. [Sitaram et al 2026]

Front Inflow Finds

What does this mean for identifying the inflows that provide galaxies with star-forming fuel? The authors reported that components in front of the galaxy — redshifted inflows and blueshifted outflows — tend to exhibit lower Hα/Hꞵ ratios compared to components behind the disk, aligning with the expectation that dust in the disk absorbs Hꞵ. In particular, these front inflows appear to be the most readily distinguished from gas in and behind the galaxy’s disk.

However, things get more complicated for gas behind the galaxy. Because the dust in the simulation is distributed nonuniformly in small clumps throughout the galaxy, it is difficult to distinguish between disk gas and gas behind the galaxy. While future simulations with improved dust modeling are necessary to resolve this issue, this study offers a useful method to distinguish inflow and outflow in dusty face-on galaxies.

Citation

“Identifying Signatures of Inflow onto Face-On Galaxies Using Balmer Decrement,” Meghna Sitaram et al 2026 ApJ 1001 87. doi:10.3847/1538-4357/ae5222

illustration of a stellar-mass object crashing through the accretion disk around a supermassive black hole

In 2019, a supermassive black hole in a galaxy 300 million light-years away woke up. Now, it’s puzzling astronomers with an unexpected slowdown in its X-ray bursts.

ZTF19acnskyy host galaxy

The fuzzy yellow galaxy at the center of this image is home to ZTF19acnskyy. [Sloan Digital Sky Survey]

Ansky Awakens

Nearly seven years ago, the Zwicky Transient Facility saw the galaxy SDSS J133519.91+072807.4 suddenly brighten at optical wavelengths, with the source given the moniker ZTF19acnskyy or “Ansky.” Within the next few years, Ansky brightened at other wavelengths, possibly signaling the first recorded case of a slumbering supermassive black hole grumbling to alertness.

In 2024, Ansky entered a new phase of behavior, exhibiting a series of semi-regular X-ray flares called quasi-periodic eruptions. The leading explanations for these flares, which have been detected from several nearby galaxies, involve a star-sized object spiraling toward a supermassive black hole. The repeating X-ray flares arise when the object crashes through an accretion disk around the black hole, or when the object loses mass each time it passes closest to the black hole. In either scenario, the time between flares is expected to decrease over time — but as new work shows, Ansky is behaving in ways that fail to fit existing theories of quasi-periodic eruptions.

An Unexpected Slowdown

plot of Ansky's X-ray flares

Soft X-ray observations of Ansky’s bursts from 2024 to 2026. These plots clearly show that in 2025 and 2026, the peak luminosities of the bursts have remained roughly constant while the time between bursts has increased. Click to enlarge. [Chakraborty et al. 2026]

Astronomers first reported on Ansky’s strange behavior in 2025, finding evidence that the time between eruptions was increasing rather than decreasing as expected. To investigate this emerging trend, Joheen Chakraborty (Massachusetts Institute of Technology) and collaborators analyzed data from the Neil Gehrels Swift Observatory’s X-ray Telescope, XMM-Newton, and the Neutron star Interior Composition Explorer (NICER).

This X-ray monitoring campaign spanned from January 2025 to January 2026 and captured 23 bursts, including 19 consecutive bursts — the most seen from a quasi-periodic eruption source to date. The bursts each lasted about three days, and the burst luminosity and total energy remained roughly constant, but the time between bursts increased smoothly from 9.9 days in January 2025 to 13.5 days in January 2026.

Possible Explanations

What physical process can produce X-ray bursts that are roughly consistent in energy and peak luminosity, last for approximately three days, and become more spaced out over time? The team considered five possibilities:

  1. A star orbiting a black hole could transfer a bit of mass to the black hole each time it draws close… but it’s not clear whether the energy of each burst would remain the same as the star loses mass, nor is it clear how a three-day eruption duration could be achieved.
  2. A star partially disrupted by a black hole could be kicked progressively farther from the black hole due to asymmetric mass loss or the reformation of its core… but this scenario cannot explain the bursts’ consistent energies and luminosities.
  3. An object orbiting a black hole with an accretion disk could be experiencing general relativistic precession… but no combination of known sources of precession can reproduce Ansky’s behavior.
  4. A second supermassive black hole could cause reflex motion of the inner black hole, changing how far the signal must travel… but even though this scenario can increase the time between bursts, the rate of increase is three orders of magnitude too small.
  5. Instabilities in the black hole’s accretion disk could trigger recurrent bursts of accretion… but it’s not yet clear how an instability scenario could produce such predictable behavior.

While none of these models can fully solve the mystery of Ansky’s slackening X-ray flares, this work provides new avenues for exploration. In the meantime, we may get new clues simply from waiting to see what this source does next!

Citation

“A Positive Period Derivative in the Quasiperiodic Eruptions of ZTF19acnskyy,” Joheen Chakraborty et al 2026 ApJL 1001 L6. doi:10.3847/2041-8213/ae548b

three images of the Sun

The Sun’s activity history, the sources of tiny jets, and how magnetic fields might impact space weather forecasts: today’s Monthly Roundup introduces a trio of recent research articles from the Astrophysical Journal that tackle hot topics in solar physics.

From 1755 to 2020: Reconstructing Centuries of Solar Activity

Since the 1970s, regular monitoring of the Sun’s magnetic field has allowed researchers to decipher the Sun’s behavior as it cycles through periods of low and high activity. But what resources exist for studying the Sun’s past behavior? To investigate the long-term behavior of the Sun, researchers reach for historical records of sunspots, which stretch back to the 1700s.

maps of simulated photospheric magnetic fields

Example maps of the simulated photospheric radial magnetic field during a period of low (top) and high (bottom) solar activity. Click to enlarge. [Jha et al. 2026]

Bibhuti Kumar Jha (Southwest Research Institute) and collaborators explored whether historical records and modern statistics could be used to reconstruct the behavior of the solar magnetic field centuries into the past. Jha’s team used recorded sunspot numbers from 1755 to 2020 as an input for their newly developed Synthetic Active Region Generator, which generates synthetic solar active regions based on known statistics of these regions. This catalog of active regions becomes the input for the Advective Flux Transport model, which simulates the active regions as they emerge and evolve, allowing for an estimation of the magnetic field across the Sun’s disk.

Jha and coauthors found that this method successfully reproduced the expected large-scale behavior of the Sun’s magnetic field across multiple solar cycles, such as the reversal of the polarity of the solar magnetic field near the peak of the activity cycle. While this work highlights the impressive results obtained from combining historical sunspot records with modern sunspot statistics, the team pointed out that this method cannot accurately reproduce all quantities because of the nonlinear nature of the underlying physics. Future work will refine the model further, and in the meantime, the team’s simulated historical magnetic field maps will be made publicly available.

Where Do the Tiniest Coronal Jets Come From?

The Sun’s atmosphere is filled with an ever-shifting maze of magnetic field lines, which reconfigure and release pent-up magnetic energy in a process called magnetic reconnection. Magnetic reconnection can launch particles and heat plasma, and it’s thought to be responsible for driving jets on a variety of scales in the Sun’s tenuous outer atmosphere, or corona. Annu Bura (Indian Institute of Astrophysics; Pondicherry University) and coauthors investigated the physical origins of the smallest of these reconnection driven jets, picoflare jets, using data from the Extreme Ultraviolet Imager on board Solar Orbiter. Solar Orbiter has ventured within 0.3 au of the Sun, and its Extreme Ultraviolet Imager has returned exceptionally precise high-energy images of our home star.

Examples of coronal jetlets

Examples of jets identified in this study. You can see an animation of this figure. [Bura et al. 2026]

Bura and collaborators identified picoflare jets by the presence of a hot, bright spire coupled with a cool, dark streak, forming a structure shaped like the letter “Y” upside down. They found that the bright and dark features were on average 650 and 490 kilometers wide, respectively, with a typical jet length of 16,900 kilometers. They also found that the bright features moved more quickly than the dark features, and the jets tended to last about 6 minutes. Overall, these measurements place the jets in between the scales expected for picoflare jets and slightly larger features called jetlets, though the energies are consistent with expectations for picoflare jets.

Using radiation magnetohydrodynamics simulations, the team explored the origins of their sample of jets. The simulations suggested that the bright features arose from hot, tenuous coronal plasma, while the accompanying dark features were due to cooler, denser plasma venturing upward from deeper in the Sun’s atmosphere, in the chromosphere. Overall, the simulations and observations support a picture in which picoflare-scale jets are driven by magnetic reconnection after magnetic flux emerges through the Sun’s surface. This echoes the formation route of larger coronal jets, suggesting that this process may apply to a wide range of physical scales.

Investigating the Influence of the Solar Polar Magnetic Field

The vast majority of our observations of the Sun have come from within a few degrees of the ecliptic plane, either from telescopes situated on Earth’s surface or from spacecraft that stuck close to the plane of our solar system. With rare but notable exceptions — the Ulysses spacecraft, which measured the Sun’s magnetic field and plasma environment from a near-polar orbit, and Solar Orbiter, which took the first-ever image of the Sun’s poles in November 2025 — the Sun’s poles have remained hidden from our instruments.

Our limited knowledge of the Sun’s polar magnetic field has consequences for our ability to model space weather events like coronal mass ejections. A team led by Xiao Zhang (Chinese Academy of Sciences; University of Chinese Academy of Sciences) has used numerical simulations to investigate how solar polar magnetic field conditions influence the propagation of a coronal mass ejection (CME) through the solar system.

Simulation results showing the propagation and expansion of a coronal mass ejection

Simulation results showing how the propagation and expansion of a CME are affected by the polar magnetic field strength. Click to enlarge. [Zhang et al. 2026]

The team simulated a CME from 4 December 2021, which was observed by the BepiColombo spacecraft at Mercury and Tianwen-1 and MAVEN at Mars. The simulations showed that as the polar magnetic field strength increases, the CME’s movement through the solar system becomes slower. CMEs typically expand as they billow outward from the solar corona and sweep past the planets; increasing the polar magnetic field strength slowed the CME’s expansion as well. A stronger polar magnetic field also alters the background solar wind, making it slower and denser. Overall, these results demonstrate that the strength of the Sun’s poorly constrained polar magnetic field can have a significant impact on the movement and evolution of a CME. In future work, Zhang’s team plans to expand their investigation to a larger sample of CMEs.

Citation

“Historical Reconstruction of Solar Surface Magnetism from Cycles 1–24 Using the Synthetic Active Region Generator and the Advective Flux Transport Model,” Bibhuti Kumar Jha et al 2026 ApJ 997 279. doi:10.3847/1538-4357/ae279a

“On the Origin of Coronal Picoflare Jets,” Annu Bura et al 2026 ApJ 1000 94. doi:10.3847/1538-4357/ae48e6

“Influence of Solar Polar Magnetic Fields on the Propagation of Coronal Mass Ejections,” Xiao Zhang et al 2026 ApJ 1000 200. doi:10.3847/1538-4357/ae4c54

JWST unfolded against a black background.

How do galaxies grow? A massive survey from JWST can help astronomers answer that fundamental question about galaxy evolution.

Time Machines

A photograph of thousands of galaxiesin one frame.

An image taken by JWST’s NIRCam instrument, the primary instrument behind the COSMOS-Web survey, of Pandora’s Cluster. Click to enlarge. [NASA, ESA, CSA, Ivo Labbe (Swinburne), Rachel Bezanson (University of Pittsburgh); Image Processing: Alyssa Pagan (STScI)]

When astronomers look into the night, they are greeted by a sky full to bursting with galaxies. But immediately after the Big Bang, none of these grand structures could have existed in our universe: all of the matter was too hot and dense to collapse into the whirlpools and ellipses we see today. We know that it took time for dark matter to collapse into halos, for gas to cool and fall into those halos, and even more time for those halos to merge together and galaxies to form. However, quantifying that story is tricky. How long did it take for the gas to cool and collapse? How often did small galaxies merge? How did the birth and death of stars play into all of this?

One way astronomers could go about answering these deep, fundamental questions in galaxy evolution would be to look at many galaxies spread across different distances. Famously, since the speed of light is fairly slow (cosmically speaking), we can only see distant objects as they appeared in the past. (This is why any aliens looking toward Earth from 65 million light-years away — from within the Virgo Cluster, perhaps — would see our planet as it was when dinosaurs roamed free.) In principle, then, by looking at a progression of galaxies farther and farther away, astronomers could convert these still images into a sort of movie of how typical galaxies look moving further and further back in time.

Seeing Red

There is a complication to this strategy, however. The farther away an object is, the more the light it emits is stretched towards redder wavelengths. As a consequence, any telescope designed to detect visible light won’t see anything; to take pictures of these galaxies, we need to build detectors that are specifically sensitive to stretched-out, near-infrared light.

This is one of the primary reasons that JWST was designed, constructed, and flung into space. It was purpose-built to collect and analyze near-infrared light from distant galaxies, and now after several years of observations and data crunching, astronomers are finally getting some answers to those fundamental questions.

The results of how galaxies’ masses relate to their total size in different redshift bins. Click to enlarge. [Yang et al. 2025]

A Massive Survey

Recently, a team led by Lilan Yang, Rochester Institute of Technology, released their analysis of one of the earliest and largest surveys JWST has undertaken, a program called COSMOS-Web. The researchers mined a patch of sky about the size of the full Moon and extracted more than 30,000 distant galaxies, most of which had never before been seen by human eyes. They measured the brightness and size of each one and grouped them according to their redshift (a proxy for their distance) and whether they were actively forming stars or not.

The team found that, unsurprisingly, galaxies tend to grow over time. Excitingly, however, they also found that for star-forming galaxies, the relationship between a galaxy’s mass and its size is fairly constant for redshifts of z = 2–8. The scaling law between them also nicely matches up with measurements taken by the Hubble Space Telescope at smaller redshifts. Beyond that, though, for redshifts of z = 8–10, it’s possible that the scaling changes, though the authors emphasize that their sample is much smaller in these distant bins.

While more data are needed to confirm whether the youngest of these galaxies grow at a different pace than their later counterparts, we can be comforted that studies like this represent just our very first peek into a whole new era of galactic evolution, and that many more insights are sure to come as JWST keeps snapping images.

Editor’s Note: This article previously contained an error relating to the size of the Milky Way. This error was corrected on 4 May 2026.

Citation

“COSMOS-Web: Unraveling the Evolution of Galaxy Size and Related Properties at 2 < z < 10,” Lilan Yang et al 2025 ApJS 281 68. doi:10.3847/1538-4365/ae0e1b

merging galaxies

What factors impact how long it takes for a supermassive black hole binary to merge? New research investigates the influence of orbital inclination on the population of merging black holes in our universe.

One Merger Leads to Another

NGC 6240

This image from the Hubble Space Telescope shows NGC 6240, the result of a three-galaxy merger that contains three nuclei, two of which appear to have active supermassive black holes. [NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)]

When galaxies merge, the supermassive black holes at their centers are thought to link up in a binary system and eventually merge as well. Evidence for these supermassive black hole pairs and their collisions is piling up: researchers have identified a small but growing number of galaxies containing two accreting supermassive black holes, and the compelling evidence for the gravitational wave background points to the existence of an immense population of supermassive black hole binaries.

With observational evidence for supermassive black hole mergers taking shape, theorists are exploring the details of these mergers. One aspect of this process that hasn’t yet been examined fully is how the relative inclination of the merging galaxies impacts the time it takes for their central black holes to merge — a factor that has the potential to shape the demographics of merging supermassive black holes across our universe.

Ready, Set, Spiral

Sena Ghobadi (Georgia Institute of Technology) and collaborators used 3D dynamical models to explore how the angle at which galaxies collide — and therefore how the black holes’ orbits are tilted relative to one another — impacts the time it takes the supermassive black holes at their centers to merge.

In the simulations, Ghobadi’s team placed a 106–108-solar-mass black hole at the center of a disk galaxy. Then, they sent a second, smaller black hole spiraling toward it from a distance of 1 kiloparsec (3,300 light-years).

The team varied the inclination of the incoming black hole’s orbit relative to the disk of the target galaxy from 0 to 75 degrees. They also explored the impact of changing the black hole masses and the galaxy’s central gas density, disk rotation speed, and gas mass fraction. For each simulation, they recorded how long it took for the incoming smaller black hole to get within 10 parsecs of the larger black hole.

simulated black hole orbits

Simulated orbits of black holes with initial inclinations of 0 (top), 25 (center), and 45 (bottom) degrees. For the 0-degree simulation, the black holes merge in 5.75 billion years. For the 25-degree simulation, the merger occurs at 7.90 billion years. The 45-degree simulation fails to merge within the lifetime of the universe. [Adapted from Ghobadi et al. 2026]

(Dis)inclined to Merge

The simulations showed a clear trend with changing inclination: a black hole with an orbital inclination greater than 20 degrees took longer to merge than those with inclinations of 0–20 degrees. For black holes approaching the merger on slightly inclined orbits, dynamical friction between the black hole and the stars and gas of the galaxy worked to drag the black hole down into the disk, decreasing its inclination over time and guiding it toward a merger. Aside from the influence of inclination, the team also found that higher-mass supermassive black holes and more rapidly rotating galactic disks tended to lead to faster mergers.

For inclinations greater than roughly 45 degrees, a dramatic transition took place, with the orbits of the incoming black holes becoming more inclined over time rather than settling down into the disk. These simulated black holes failed to merge in the allotted time of 14 billion years.

With highly inclined binaries failing to merge within the lifetime of the universe, this suggests that the dual active galactic nuclei and the supermassive black hole binaries that produce gravitational waves in the universe today are the result of binaries with initial inclinations of 20 degrees or less.

Citation

“Evolution of Supermassive Black Hole Pairs on Inclined Orbits in Postmerger Galaxies,” Sena Ghobadi et al 2026 ApJ 999 131. doi:10.3847/1538-4357/ae40bc

blue supergiant

Prior to exploding, massive stars advance through action-packed evolutionary stages that are exciting but often difficult to fully decipher. A recent study focuses on a unique late-stage star to better understand its properties and evolution.

To B[e] a Supergiant

HD 62623 disk image

Very Large Telescope Interferometer image of the circumstellar disk around the B[e] supergiant star HD 62623. The colors indicate the rotation of the disk with blue coming toward us and red going away. [ESO/F. Millour; CC BY 4.0]

After depleting their cores of hydrogen, massive stars journey off the main sequence through a series of evolutionary phases before ending in dramatic supernova explosions. A massive star’s post-main-sequence evolution is intense, often sloughing off layers of material that can settle into a circumstellar disk. The B[e] supergiant phase describes a blue supergiant star surrounded by a cool, dense circumstellar disk where oxygen is more abundant than carbon. These environments often lock up carbon atoms in carbon monoxide molecules, leaving excess oxygen available to form other molecules including SiO, TiO, and water vapor. These molecules can survive under different physical conditions, making them key tracers of the environments around B[e] supergiants.

One particularly interesting B[e] supergiant, LHA 115-S 18, has been the subject of numerous studies but remains poorly constrained. The star exhibits significant variability both in brightness and emission features on timescales of days to years, and previous works have suggested that the star may have an as-yet unconfirmed binary companion. Molecular line emission from CO and TiO have been identified in LHA 115-S 18, indicating a circumstellar disk, but to date, water vapor emission has not been identified in any B[e] supergiant. Identifying more complex oxygen-bearing molecules like water will further reveal the physical properties and possible binary companion of LHA 115-S 18.

Identifying Emission in LHA 115-S 18

To characterize the emission around LHA 115-S 18, María Laura Arias (Institute of Astrophysics La Plata; National University of La Plata) and collaborators obtained high-resolution near-infrared spectroscopy of the star using the Immersion Grating Infrared Spectrometer on the Gemini South telescope. From the high-resolution spectra, the team identified several atomic emission lines indicative of the star’s gaseous envelope, revealing the structure of material around the star: an inner hot disk of ionized material and an outer cool disk of neutral material. Looking at molecular emission from carbon monoxide — a tracer of both gas motions and stellar age — the authors confirmed the presence of a rotating ring of gas around LHA 115-S 18 and determined that the star is an evolved, post–red supergiant object.

LHA 115-S 18 spectrum

Spectrum of LHA 115-S 18 (black) with the model spectrum composed of water vapor (red, top three panels) and water vapor, CO, and hydrogen emission (red, bottom two panels) overplotted as well as residuals (gray). [Arias et al 2026]

Through computing a synthetic spectrum to compare to the observed spectrum, the authors identified many water vapor emission lines in the circumstellar environment around LHA 115-S 18. While water vapor has been detected in other evolved late-type stars, this is the first detection of water vapor from a B[e] supergiant star. For water vapor to survive the star’s intense radiation, it must exist in a dense, cool, heavily shielded disk around the B[e] supergiant.

Sustaining a cool disk around such a hot star indicates that the circumstellar environment around LHA 115-S 18 is complex and likely shaped by binary interaction. With emission features characteristic of both cool and hot evolved stars, this particular B[e] supergiant presents itself as a unique object holding critical insights into the late-stage evolution of massive stars. Further multiwavelength observations of LHA 115-S 18 will constrain its potential binarity and reveal a possible evolutionary link between B[e] supergiants and other late-stage evolutionary phases of massive stars.

Citation

“High-resolution Near-Infrared Spectroscopy of the B[e] Supergiant LHA 115-S 18: Discovery of Hot Water Vapor Emission,” María Laura Arias et al 2026 ApJL 1000 L49. doi:10.3847/2041-8213/ae524a

The Submillimeter Array at the summit of Maunakea in Hawaiʻi.

The Event Horizon Telescope (EHT), the facility that delivered humanity’s first-ever picture of a black hole, can produce some of the sharpest images in all of astronomy. But turning the EHT’s raw data into images is a complex process involving messy statistics and powerful algorithms. Recent work presents a potential upgrade to that process: for the first time in long-baseline interferometry, it may be possible to model everything everywhere all at once.

The Hardest Eye Test

The EHT has some of the sharpest eyes in all of astronomy. With its effective resolution of just 20 microarcseconds, in principle you could use it to read a newspaper in New York while sitting at a cafe in Paris. But this planet-spanning instrument (it relies on data from radio telescopes on four continents) doesn’t snap pictures like an ordinary camera. Instead, each pair of telescopes measures something called an “interferometric visibility,” which is related to a single Fourier component of the actual underlying image.

A photograph of an orange ring surrounding a dark center.

The first image of a black hole, constructed from Event Horizon Telescope data taken in 2017. [EHT Collaboration; CC BY 4.0]

Combining these components into an image is a process fraught with assumptions and modeling choices. Since the EHT doesn’t have an infinite number of telescopes, each measurement can be mapped to infinitely many images. This forces researchers to choose how to “regularize” this space of images to select one best picture. Making things harder, they also must contend with all the typical issues of real-world data collection. Each telescope has slight calibration errors, and every data point is affected by weather and temperature-dependent processes.

Typically researchers break the problem down into several stages: first calibrate the data, then regularize and construct the best-fitting image, then analyze that image to constrain the actual physics you care about like the width of the ring surrounding a black hole. This is how the original EHT publications went about their groundbreaking work on the now-iconic glowing ring around the supermassive black hole in the galaxy Messier 87 (M87*).

A New Approach

Recent work led by Paul Tiede (Black Hole Initiative at Harvard University) suggests an alternative process. Instead of separating the stages of analysis as described above, the team demonstrated that one could fit everything simultaneously in a framework they call hierarchical interferometric Bayesian imaging, or HIBI.

A multi-panel plot of images of an orange blob with a tail. All images are very similar.

A comparison of the new HIBI technique (referred to as “Comrade” here) and a traditional algorithm called CLEAN. Click to enlarge. [Tiede et al. 2026]

By fitting all parameters that go into an image together, the method doesn’t select one “best” image. Instead, by allowing the pixel-by-pixel intensities, calibration parameters, and underlying physics to inform one another during inference, HIBI explores the full range of images consistent with the data. This prevents the degeneracies that plague the traditional approach, where image and calibration estimates can trade off against each other in misleading ways. The team validated HIBI on synthetic data mimicking the EHT’s 2017 setup, showing that it reliably recovered a range of source shapes with well-calibrated uncertainty estimates.

Even more exciting, the team demonstrated that it’s possible to skip the image construction step altogether and go straight to the science. By fitting parameters describing the physics underlying a scene, the team was able to constrain the width of the ring around M87* without any reference to a picture. They predict that this technique could be crucial for extracting information when future instruments like the Next Generation Event Horizon Telescope observe more distant black holes that are only marginally resolved. Though we’ll likely have to wait years for these next-generation telescopes, work like this ensures that astronomers will be able to squeeze as much science from them as possible once these new facilities are ready.

Citation

“Hierarchical Interferometric Bayesian Imaging,” Paul Tiede et al 2026 ApJ 997 262. doi:10.3847/1538-4357/ae2749

comet C/2023 P1

Researchers tracked the tail of comet C/2023 P1 (Nishimura) as it interacted with a string of coronal mass ejections, leading to the first-ever quantitative analysis of a cometary tail detachment event.

C/2020 F3 (NEOWISE)

A photo of comet C/2020 F3 (NEOWISE) showing its narrow bluish ion tail and broader white dust tail. [Juan lacruz; CC BY-SA 4.0]

A Comet’s Journey

When comets journey into the inner solar system, they tend to do so sporting two tails: a dust tail that sweeps back from the comet along its curved trajectory and an ion tail that points away from the Sun, in the direction of the interplanetary magnetic field.

The ion tail, which forms when ultraviolet light from the Sun ionizes gas in a comet’s fuzzy coma, interacts with structures in the solar wind, causing it to shift, sputter, and sometimes even disconnect entirely. Now, for the first time, researchers have quantified the timescales involved when a comet loses — and regrows — its tail.

The Tale of a Tail

Shaheda Begum Shaik (George Mason University; US Naval Research Laboratory) and collaborators studied this phenomenon in observations of the comet C/2023 P1 (Nishimura) from 1 to 14 September 2023. In high-resolution images from the Solar Orbiter Heliospheric Imager, Shaik’s team analyzed the dynamics of C/2023 P1’s tail as the comet braved blustery solar wind conditions in the inner solar system.

In a two-week period, the comet underwent four separate tail disconnection events, in which the connection between the ion tail and the comet was severed. Each of these events coincided with the passage of a coronal mass ejection: a tangled mass of solar plasma and magnetic fields ejected from the Sun’s outer atmosphere.

tail disconnection event observations

Solar Orbiter Heliospheric Imager observations of the 11 September 2023 tail disconnection event, which was driven by a passing coronal mass ejection (CME). [Shaik et al. 2026]

Lizard-Like Regrowth

Focusing on the tail disconnection event with the highest-resolution and highest-cadence data, Shaik’s team observed constant small-scale fluttering of the ion tail, reflecting the buffeting of the tail by the solar wind. The tail then developed a kink, which the team speculated is due to compressed solar wind plasma piling up in front of an oncoming coronal mass ejection. The wide-field images show the coronal mass ejection advancing upon the comet and the comet’s tail seemingly being sliced in two.

The free-floating tail segment sped away from the comet at roughly 295 km/s, likely indicating that the tail became caught up in and was transported by the flank of the coronal mass ejection as it barreled past the comet. The timescale and geometry of the event suggest that the interaction of the coronal mass ejection’s magnetic field with the comet’s tail was responsible for the disconnection.

Over the following 24 hours, the comet’s tail slowly regrew at a rate of 86 km/s to its original length of 1.9 million kilometers. The rate of regrowth is likely determined by several factors, such as the rate at which the comet produces ions and the local magnetic field configuration. This work represents a first look at the quantitative behavior of a tail disconnection event, paving the way for future investigations of cometary behavior and a greater understanding of the complex magnetic and plasma environment of the inner solar system.

Citation

“The First Quantitative Study of Cometary Tail Regrowth Following a Coronal Mass Ejection-Driven Disconnection Event,” Shaheda Begum Shaik et al 2026 ApJ 999 60. doi:10.3847/1538-4357/ae3bdb

merging galaxies

The galaxy NGC 4486B appears calm and collected, but its center may have been roiled by a recent merger of supermassive black holes. New modeling explores the stellar dynamics that support this hypothesis.

Strange Center

NGC 4486B double nucleus

Kinematic maps of NGC 4486B showing the locations of the two peaks of its double nucleus. Click to enlarge. [Adapted from Tahmasebzadeh et al. 2026]

Astronomers have known for 30 years that NGC 4486B, a compact elliptical galaxy near the center of the Virgo cluster, has a double nucleus. More recently, JWST observations revealed that the galaxy houses a black hole of 360 million solar masses, which is unusually large compared to the galaxy’s stellar mass of 9 billion solar masses. The two nuclei are roughly 40 light-years from the apparent center of the galaxy, and the black hole also appears to be offset from the galactic center by 20 light-years.

Now, a team led by Behzad Tahmasebzadeh (University of Michigan; Villanova University) has investigated the possibility that NGC 4486B’s double nucleus and off-center black hole can be traced to the aftermath of a supermassive black hole merger.

Simulating Kinematics

In this scenario, the black hole is displaced from the galaxy’s center because of a “kick” it received when it underwent a merger. The double nucleus is a sign of an eccentric nuclear disk: a central disk of stars on aligned elliptical orbits created when merging supermassive black holes disturb an initially orderly disk of stars.

plot of kick magnitude versus mass ratio

Estimated black hole kick magnitude as a function of the initial mass ratio of the black hole binary. Click to enlarge. [Tahmasebzadeh et al. 2026]

Tahmasebzadeh and collaborators performed dynamical modeling to test this hypothesis and understand what types of stellar orbits would be necessary to reproduce the kinematic signature of NGC 4486B’s center seen with JWST. The simulation results called for a blend of prograde and retrograde stellar orbits that closely resembled what is expected for an eccentric nuclear disk. From the properties of the simulated stellar disk, the team estimated that the mass ratio of the merging black holes was >0.15.

To explore this scenario further, the team carried out N-body simulations of the post-merger black hole’s behavior. These simulations showed that after being booted from the galactic center by the post-merger kick, the black hole returns to the center quickly — within 10–80 million years, depending on the kick strength. Because NGC 4486B’s supermassive black hole is notably off center, this suggests that the merger occurred recently.

Galaxy Merger Versus Black Hole Merger

Tahmasebzadeh’s team tested two other theories that could explain the appearance of NGC 4486B’s nucleus: dynamical buoyancy and a pre-merger supermassive black hole binary. Neither of these scenarios could reproduce the offsets seen in the center of the galaxy.

The team noted that NGC 4486B appears to be in equilibrium, with no sign of a recent merger that could have plunked a second supermassive black hole into the galaxy. How can this fact be reconciled with the evidence for a recent black hole merger? Turning again to simulations, the team found that if the black hole binary’s orbit was aligned with the galaxy’s rotation, the binary could have become trapped in a resonance that greatly delayed the merger of the black holes. This makes it possible that NGC 4486B underwent a galaxy merger in the distant past, but its central black hole merged only recently, leaving signs of a long-ago merger that has otherwise faded from view.

Citation

“JWST Observations of the Double Nucleus in NGC 4486B: Possible Evidence for a Recent Binary SMBH Merger and Recoil,” Behzad Tahmasebzadeh et al 2026 ApJL 1001 L14. doi:10.3847/2041-8213/ae52ef

gas giant orbiting white dwarf

Orbiting a white dwarf, the exoplanet WD 0806b is the subject of a recent study using JWST to measure the atmospheric conditions governing the planet.

Directly Imaged Exoplanet WD 0806b

Most of the 6,000 and counting exoplanets discovered thus far have been detected due to their impacts on their host star — passing in front of the star and causing it to dim, or gravitationally tugging on the star and causing it to wobble. On rare occasions, though, astronomers have been able to catch the exoplanet itself through direct imaging. Directly imaged exoplanets offer key insights that cannot be obtained through indirect detection methods. Luminosity measurements and spectral emission features allow astronomers to more directly measure planet mass, radius, and composition otherwise inferred from the host star.

WD 0806b system

NIRCam image showing host star WD 0806 circled in orange and the location of exoplanet WD 0806b marked by the orange arrow. [Lew et al 2026]

Included in the about 90 distant planets that have posed for a picture is WD 0806b, a rare exoplanet companion trotting around a white dwarf at an orbital distance of 2,500 au (50 times the distance from the Sun to the Kuiper belt!). Originally discovered with the Spitzer Infrared Array Camera in 2011, WD 0806b is the second-coldest directly imaged exoplanet to date. With JWST’s high-precision photometric and spectroscopic capabilities, WD 0806b provides a unique opportunity to probe the atmospheric chemistry of cold giant planets and take steps toward understanding the co-evolution of white dwarfs and their surviving exoplanets.

WD 0806b’s Atmospheric Abundances from JWST

Aiming to characterize the physical properties and atmospheric composition of WD 0806b, Ben W.P. Lew (Bay Area Environmental Research Institute; NASA Ames Research Center) and collaborators used JWST’s Near-Infrared Camera (NIRCam) and Near-Infrared Spectrograph (NIRSpec) to obtain high-resolution imaging and spectroscopy of the exoplanet. Combining these observations, prior lower-resolution observations, and evolutionary planet models, the authors estimated the physical properties of WD 0806b including mass, radius, surface gravity, and effective temperature.

WD 0806b spectrum

NIRSpec spectrum of WD 0806b with best-fit model spectra overlaid. [Lew et al 2026]

From the derived physical properties, the authors modeled the NIRSpec spectrum to estimate molecular abundances and elemental abundance ratios in the atmosphere of WD 0806b. They obtained measurements of multiple molecules including carbon dioxide, carbon monoxide, and ammonia; these molecular abundances offer the opportunity to test chemical equilibrium and disequilibrium as well as eddy diffusion, or bulk mixing, in the planet’s atmosphere. The authors developed a novel chemical analysis framework to determine how bulk mixing varies with altitude in WD 0806b and reported the first observational evidence that mixing becomes weaker at higher altitudes in exoplanet atmospheres. This result points to the need for future studies exploring the impact of these chemical processes on spectra and photometry, which are essential to characterizing cold giant planets.

This study highlights how high-precision JWST data can reveal a rich collection of atmospheric conditions, chemical composition, and physical processes occurring in cold giant planets. With such a wide orbit from its host white dwarf, WD 0806b serves as an interesting case study for how giant planet composition may reflect the formation and evolutionary history of the overall system. Future observations of and comparisons to similarly cold giant planets will further uncover how atmospheric characterization may fit into our understanding of exoplanets and their histories.

Citation

“JWST Spectral Retrieval of Cold Directly Imaged Planet WD 0806b and the First Measurement of Altitude-dependent Kzz in Exoplanet Atmospheres,” Ben W.P. Lew et al 2026 AJ 171 227. doi:10.3847/1538-3881/ae4747

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