By taking general relativity into higher dimensions, a trio of physicists has proven that a mathematical pattern of ripples in space-time geometry could give rise to naked singularities and microscopic black holes.

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

In theory, this question can be answered by extracting the properties of merging black holes — mass, spin, and the like — from gravitational wave observations and comparing these properties against model predictions from different formation pathways. In reality, this is exceedingly difficult, as certain merger pathways can produce a wide variety of results, depending on assumptions or fine tuning.

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.

Their modeling tests combinations of multiple populations, including mergers in isolated binary systems, triple-star systems, and dense environments like star clusters. They also include a potential contribution from higher-mass mergers involving black holes that have merged previously. Using this framework, Stegmann’s team found that the observed spin–orbit tilt distribution is best matched by a model dominated by mergers in triple-star systems, with some contribution from other sources. Specifically, this finding suggests that most mergers occur in hierarchical triple systems, which naturally predict an excess of 90-degree spin–orbit tilts without any fine tuning. Hierarchical triples contain an inner close binary with a distant outer companion; in these systems, relativistic spin precession, gravitational wave emission, and oscillations in eccentricity and inclination work to tilt the black holes in the inner binary by 90 degrees.

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

The post Third Star’s the Charm: Most Merging Black Holes Might Be in Triple Systems 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: 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).

When astronomers look at different active galaxies (read: galaxies with active supermassive black holes at their core), we see a range of phenomenologies related to their brightness, spectra, morphologies, and more. The unified model of AGNs seeks to explain these different AGN appearances simultaneously by positing that they all have the same physical structure, and we are just viewing them from different angles, hence seeing different features.

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).

To explain the observed morphology in Figure 1, the authors compare three different interpretations based on this new high-resolution imagery together with the results of previous studies looking at other scales and the spectrum of the AGN core. Each interpretation is illustrated and briefed in Figure 3. The first interpretation is in keeping with the unified model of AGNs: a geometrically and optically thick torus of dust surrounds the inner region. In this interpretation, the surface of the dusty torus re-radiates light from the accretion disk to produce most of the mid-infrared emission. Additional mid-infrared emission could come from localised concentrations of gas or interactions between the outflow and the jet. The authors immediately disfavour this explanation, as other studies have shown bright ionised emission at the location of the would-be torus, which is not expected if an optically thick torus were to be present. Hence, these new observations somewhat challenge the one “flavour” of the unified model of AGNs.

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.

The post I Spy with My Large Binocular Eyes: A Dusty Torus Around a Supermassive Black Hole? appeared first on AAS Nova.

The core of the brightest galaxy in the cluster Abell 402 contains a curious void. New observations suggest that an ultra-massive black hole could have excavated this feature.

At the Center of the Center of a Cluster

Abell 402 is a galaxy cluster located roughly 4 billion light-years away, and at its center is a giant elliptical galaxy called A402-BCG. Zooming in on the heart of this galaxy, astronomers using the Hubble Space Telescope discovered a dark region that they suspected was due to a cloud of dust blocking the starlight from the galaxy’s center.

In a recent research article, a team led by Michael McDonald (Massachusetts Institute of Technology) investigated this dark region to test the dust-cloud hypothesis and explore other explanations.

McDonald’s team compiled new JWST Near-Infrared Camera data, archival Hubble imaging, and spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope. The new JWST images show a prominent dark feature at the center of A402-BCG, plus a bright source directly beside it.

Not Hidden, but Missing

If the dark feature at the center of A402-BCG is a dust cloud, the cloud would be less obscuring at the near-infrared wavelengths captured by JWST than at the optical wavelengths sampled by Hubble. However, the feature was equally dark in the JWST images, leading the team to rule out the dust-cloud hypothesis.

Instead, they favor a scenario in which the dark feature is due to an absence of stars rather than the presence of obscuring dust. The team estimated that 2 billion solar masses of stars are missing — equivalent to 1% of the stellar mass of the galaxy. What’s more, the cavity is situated in a larger region of constant surface brightness called a core, in which there are fewer stars than expected.

The Dynamical History of A402-BCG

McDonald and coauthors suggested that the missing stars in A402-BCG’s core and cavity were ejected by at least one supermassive black hole binary. They estimated that the core region, which is roughly 6,500 light-years across, was excavated by a 50 billion solar mass black hole. This epic black hole may be the result of a past merger and is likely located at the infrared-bright spot on the border of the cavity, as this source’s spectral energy distribution resembles that of an actively accreting black hole.

MUSE spectroscopy provided evidence for a second black hole. These data revealed two pockets of ionized gas — one coincident with the infrared-bright source, the other on the opposite side of the cavity — as well as two distinct sets of emission lines consistent with a black hole binary totaling 60 ± 20 billion solar masses. (The team noted that alternate explanations for the second source, like a compact starburst, were less likely but couldn’t be ruled out.)

The team favors a scenario in which these black holes are slowly spiraling toward one another, ejecting stars from the galaxy’s center as they move and carving out a deep deficit of stars. This stellar cavity sits within a larger region of stellar scarcity that was scooped out by a past supermassive black hole merger that created the ultra-massive black hole present in the galaxy today. Simulations suggest that only about 0.5% of massive galaxies are in this phase of evolution at a time, so we may have caught A402-BCG in a fascinating moment — one that provides new clues about how to search for ongoing black hole mergers in other galaxies.

Citation

“A Kiloparsec-Scale Stellar Cavity in the Center of A402-BCG May Be Caused by Dynamic Interactions with an Ultramassive Black Hole,” Michael McDonald et al 2026 ApJL 1002 L19. doi:10.3847/2041-8213/ae5bbe

The post Into the Void: Investigating the Heart of a Giant Elliptical Galaxy appeared first on AAS Nova.

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.

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

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

The post A Black Hole’s Puzzling X-Ray Bursts appeared first on AAS Nova.

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

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.

(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

The post How Tilted Orbits Impact Supermassive Black Hole Collisions appeared first on AAS Nova.

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.

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.

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

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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

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.

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

The post Signs of a Supermassive Black Hole Merger in NGC 4486B appeared first on AAS Nova.

Researchers have undertaken a new search for a supermassive black hole binary, placing limits on its properties and exploring a promising technique for simultaneously analyzing electromagnetic and gravitational wave data.

Narrowing the Search for Supermassive Black Hole Binaries

In 2023, astronomers announced the discovery of compelling evidence for the gravitational wave background: the collective murmurs and rumblings of distant supermassive black hole binaries. The time may now be ripe for the natural next phase of discovery: the detection of gravitational waves from an individual supermassive black hole binary.

One of the most promising candidates for this search is 3C 66B, a poetically named elliptical galaxy roughly 300 million light-years away. More than 20 years ago, researchers discovered that the radio source at the heart of this galaxy wobbles to and fro in a way that’s consistent with the elliptical paths of supermassive black holes in a close binary. Further work predicted that the gravitational waves produced by this binary would have a frequency of about 60 nanohertz and potentially be within the observational reach of current methods.

Pulsar Timing Array

Jacob Cardinal Tremblay (Max Planck Institute for Gravitational Physics and Leibniz University Hannover) and collaborators conducted a search for gravitational waves from the candidate supermassive black hole binary in 3C 66B using the Parkes Pulsar Timing Array (PPTA).

A pulsar timing array is a collection of pulsars monitored for signs of passing gravitational waves. Pulsars are the condensed, rapidly spinning cores of high-mass stars that exploded as supernovae. Named for their characteristics radio pulses, these extreme stars spin with exceptional regularity, and the passage of a gravitational wave can shrink or expand spacetime enough to speed up or delay the arrival of a pulsar’s pulses. By searching for coordinated changes in pulse arrival times from a collection of pulsars, researchers hope to detect low-frequency gravitational waves that are inaccessible to observatories like LIGO.

Researchers have previously searched for gravitational waves from 3C 66B in data from other pulsar timing arrays, such as the North American Nanohertz Observatory for Gravitational Waves, and no black hole binary has been detected. This is the first search of the third PPTA data release, which contains measurements of 32 pulsars over 18 years, providing a long baseline to search for the slow undulations of low-frequency gravitational waves.

Placing Limits

Using Bayesian statistical methods to analyze their pulsar timing data, the team was unable to confirm or rule out the presence of a supermassive black hole binary in 3C 66B. However, they were able to place limits on its properties, such as the chirp mass and the amplitude of the signal, and certain limits were more stringent than those placed by existing electromagnetic data.

While this analysis didn’t result in the first-ever detection of gravitational waves from a single supermassive black hole binary, it did allow the team to test a new method that could someday play a role in precision cosmology. This method simultaneously analyzes electromagnetic and gravitational wave data from known supermassive black hole binaries, establishing these sources as “standard sirens” that can complement standard candles like Type Ia supernovae for measurements of the expansion rate of the universe.

Citation

“A Multimessenger Search for the Supermassive Black Hole Binary in 3C 66B with the Parkes Pulsar Timing Array,” Jacob Cardinal Tremblay et al 2026 ApJL 998 L42. doi:10.3847/2041-8213/ae3c98

The post A Search for a Supermassive Black Hole Binary 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 z = 7.08 quasar ULAS J1120+0641 May Never Reach a “Normal” Black Hole to Stellar Mass Ratio
Authors: Meredith A. Stone et al.
First Author’s Institution: University of Arizona
Status: Published in ApJ

The first galaxies in the universe emerged out of an archaic age of darkness. Like luminous factories, they started rapidly churning out stars, spilling light into the cosmos. This process of star formation continues to the present day. In some galaxies, it occurred at astonishing rates, with the equivalent of thousands of times the mass of the Sun being assembled into stars in a single year. At other times, it came to a slow crawl, with all fresh reserves of star-building gas seemingly exhausted. Yet when the gears of star formation ground to a halt, certain events were able to send them spinning again.

One of the most spectacular of these is a merger, a train-wreck collision between two galaxies. Images of these events are often breathtaking, showing arms of light twisting together and vast stellar streams being violently cast away. Mergers directly increase the stellar mass (the mass of all stars) of galaxies by combining two into one. The intense gravitational interactions between the galaxies involved can also disrupt stagnant pools of gas, igniting a new burst of star formation. Thus, interactions between galaxies can be a significant driver of their growth.

Sometimes, a reservoir of matter is driven toward the center of a galaxy due to a “secular” process (one that occurs without external intervention) or from a merger. At the galactic nucleus, the infalling streams of matter encounter a supermassive black hole. The matter falls into a swirling accretion disk, heating to extreme temperatures and furiously glowing. If the black hole is massive enough and the gas falls in quickly enough, the accretion disk can outshine all of the stars in the galaxy, and we call such a source a quasar. The intense radiation produced by a quasar can impact the entire rest of the galaxy, either suppressing the formation of new stars or sometimes igniting it.

Thus, a galaxy has an important role in the growth of its central supermassive black hole, and vice versa. This connection manifests in complicated ways. Most strikingly, it is thought to be the cause of the correlation between a galaxy’s stellar mass and its central black hole mass. In the nearby universe, galaxies have stellar masses around a thousand times greater than their black hole masses. JWST, our most powerful tool for investigating early galaxies, has given us unprecedented insight into whether this holds up in the distant universe. Though the jury is still out, many researchers are convinced that the answer is a resounding no. We’ve found distant black holes that appear to be nearly equal in mass to their host galaxies, something that’s unfathomable in the local universe.

However, this raises a key question. Black holes and their galaxies grow together, and they started on nearly equal footing. So why do all of the galaxies in the nearby universe appear so much more massive than their black holes? Today’s article underscores this puzzle, pushing it to the breaking point. The authors examine a well-studied quasar, ULAS J1120+0641 (hereafter J1120), which we see as it appeared just 750 million years after the Big Bang. This source has a supermassive black hole containing an astounding 20% the mass of its host galaxy. The shocking part is that, even after carefully accounting for all of the ways this galaxy could grow in the future, there appears to be no way for J1120 ever to reach “normal” proportions.

Through the Looking Glass, ULAS J1120

First, the authors analyze the key observations of J1120 obtained to date. In addition to observations from JWST, this source has been targeted by some of the most powerful astronomical facilities, including the Hubble Space Telescope (optical and near-ultraviolet), the Chandra and XMM-Newton observatories (X-rays), the Atacama Large Millimeter/submillimeter Array (radio/millimeter), and numerous other ground-based telescopes. This incredible dataset provides a detailed picture of J1120 across the electromagnetic spectrum, spanning X-rays to radio emission.

The authors compare various measurements of the black hole’s mass and find that multiple methods yield a similar result of about a billion and a half times the mass of the Sun. Turning to the host galaxy, they estimate the mass of the visible stars, which is more complicated than it sounds — you can’t exactly count them, since the enormous distance between us and J1120 causes it to appear as just a fuzzy blob. They combine this mass with the mass of newly forming stars that are buried in dust and obscured from our view. The mass of a nearby galaxy that’s actively merging with J1120 is added to this sum. Finally, the authors compute how many stars could form in the future from all of the gas left in the galaxy, and they throw this into the total.

Even with all of these components, the host galaxy would only be 10 times more massive than the black hole at the center. This ratio is a far cry from the factor of a thousand we expect for normal galaxies in the local universe!

A Train Wreck of Train Wrecks

Well, if one merging galaxy won’t do it, what if J1120 merges with literally every single other nearby galaxy? The authors use new JWST data to count all sources near the quasar (Figure 1) and measure their stellar masses. Going further, they estimate how many galaxies their technique may have missed and add all of these to the pile. Not done yet, they finally conclude by making a rough approximation of how much loose gas is in these nearby galaxies, and compute how much extra mass could exist in stars born from this fresh material. Assuming that J1120 survives the full-frontal assault, being battered by mergers from each of its neighbors in turn, its total stellar mass would grow by quite a large factor.

What’s the final result? Shockingly, even after all of this growth, the stellar mass of J1120 would still only be about 40 times that of the central black hole. That’s 25 times less than we’d expect from a nearby galaxy! Even if the black hole never grows again, it appears that this galaxy will never reach “normal” proportions. So why is it that, when we look around at the local universe, there’s nothing like J1120? The authors point out that galaxies near J1120 would be missed by their methods if they are obscured by thick shrouds of gas and dust. Such sources would increase the estimated mass that could be contributed by mergers. On the other hand, maybe J1120 will adopt the strategy of the blue whale, filter feeding on the extremely sparse matter between galaxies, yet growing to enormous proportions.

A fascinating final possibility is that galaxies like this one do exist in the nearby universe. With their black hole switched off, all we would be able to see is a relatively small package of stars. Place such an object far enough away, and we might miss it entirely! Whether galaxies like J1120 achieved normal proportions through unknown mechanisms or are lurking in the far fringes of the local universe, studies like this one shine light on the amazing connection between black holes and their host galaxies. In the future, they will be one key piece in the puzzle of the endlessly complicated past of our own galaxy and the universe at large.

Original astrobite edited by Will Golay.

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.

The post Forever Alone: A Black Hole Destined to Stay Too Big appeared first on AAS Nova.

Where do the mysterious cosmic messengers called neutrinos come from? Researchers search for a connection between neutrinos and accretion flares from black holes.

Seeking Connections

Neutrinos — neutral, nearly massless elementary particles — are generated by natural particle accelerators across the universe. Facilities like the IceCube Neutrino Observatory, which employs detectors buried a mile deep in Antarctic ice, spot neutrinos from distant astrophysical sources, but matching these neutrinos to their sources is no easy task.

Thus far, researchers have discovered a compelling connection between neutrinos and distant active galactic nuclei, which are powered by the accretion of gas onto supermassive black holes. The active galactic nucleus phase of a black hole tends to be long lived, with activity lasting hundreds of thousands of years or more, making these nuclei lasting sources of neutrinos.

Sampling Flares

Recently, researchers have found tentative evidence for coincident neutrinos from short-lived accretion events like tidal disruption events, in which a star is torn apart and accreted by a black hole. These studies have uncovered a potential connection between neutrinos and tidal disruption events with mid-infrared echoes, signaling the presence of obscuring dust.

To investigate whether there is any connection between neutrinos and short-lived accretion events, Megan Wang (Massachusetts Institute of Technology) and collaborators first compiled a sample of 99 black hole flares observed by NEOWISE. These flares were selected for their strong mid-infrared emission, location in the nuclei of galaxies, and a fast rise and slow decline. The team applied additional selection criteria to remove other bright transients, such as supernovae, and retain only tidal disruption events and active galactic nucleus accretion flares.

For the neutrino side of the equation, Wang’s team turned to IceCube’s most recent catalog of neutrino events from astrophysical sources. In total, they compiled a sample of 68 events for which the odds of the source being astrophysical was greater than 50%, and for which the directional uncertainty was below 50.

No Coincidences

For a flare and a neutrino to be considered spatially and temporally coincident, the neutrino must arrive within one year of the flare, and the flare must fall within the 90% certainty contours of the neutrino. Ultimately, Wang’s team found no neutrinos that fulfilled both criteria and only one that was spatially but not temporally coincident with a black hole flare.

This result appears to be at odds with previous studies that found several neutrinos that were coincident with tidal disruption events. Wang and collaborators noted that while this work finds no association between neutrinos and black hole flares, it’s possible that the team is studying a different population of accretion events.

For example, while the previous neutrino-associated flares were flagged for having strong mid-infrared emission, they differ from the current sample in that they were detected at optical wavelengths. The flares sampled in this work were detected in the mid-infrared and have little to no optical emission, potentially highlighting intrinsic differences compared to previous samples.

Future work, including studies that leverage upcoming datasets from the Vera C. Rubin Observatory, the Roman Space Telescope, and the NEO Surveyor, can address this question further and search for connections with specific populations of black hole flares.

Citation

“Testing the Association of Supermassive Black Hole Infrared Flares and High-Energy Neutrinos,” Megan Wang et al 2026 ApJL 998 L29. doi:10.3847/2041-8213/ae3f90

The post Do Black Hole Flares Generate Neutrinos? 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: X-Ray Investigation of Possible Super-Eddington Accretion in a Radio-Loud Quasar at z = 6.13
Authors: Luca Ighina et al.
First Author’s Institution: Harvard–Smithsonian Center for Astrophysics and Italian National Institute for Astrophysics
Status: Published in ApJL

Quasars are some of the most extreme objects in the entire universe. Despite being as far as tens of billions of light-years away, they nonetheless can appear as bright as some stars in our own Milky Way. To put their brightness in perspective, one just has to consider the Sun. Compared to puny human scales, our star is a truly gargantuan object. It’s a fully functional fusion reactor, churning hydrogen into helium in its core and outputting an unfathomable amount of energy in the process. This glowing furnace is so bright that it can cook us with the heat of an oven during the day, even at a distance of more than 90 million miles (about 8 light-minutes). That distance dramatically dilutes the radiation of the Sun by the time it reaches us, as we only receive a small sliver of its total output, and yet we can still feel its heat pounding down on us when we stand beneath a clear summer sky.

However, if one were to move the Sun about 30 light-years away, it would appear completely unremarkable. You’d need to be under relatively dark skies to even spot it! The vastness of space would simply crush the output of our solar engine; however, if you place a luminous quasar at that same 30 light-year distance, its searing radiation would seem to effortlessly cross the cosmic gulf looming between the stars, scorching us relentlessly with the same heat as the Sun does today. The power of a quasar simply puts our star to shame.

Still, even quasars have limits. The source of power for these objects is a supermassive black hole. The supermassive black hole that lives at the center of our Milky Way is currently dormant. However, many supermassive black holes (especially in the early universe) actively gulp down matter, releasing tremendous energy that escapes in the form of radiation across the electromagnetic spectrum. The escaping photons bump into particles on their way out, exerting an outward pressure. If enough light is unleashed by the quasar, this pressure will actually balance against the pull of gravity, cutting off the food supply for the black hole. This negative feedback loop means that a given quasar has an upper limit to its brightness, called the Eddington luminosity, and to the speed at which it accretes matter, called the Eddington rate. The authors of today’s bite examine a particularly misbehaved quasar that seems to violate even these extreme limits.

It’s a Bird! It’s a Plane! It’s a Jet?

The authors observed the quasar RACS J032021.44−352104.1 (RACS J0320−35 for short) with several radio observatories, including the Giant Metrewave Radio Telescope, the Australia Telescope Compact Array, and the Australian Large Baseline Array. Combining this data with publicly available observations, they find that the source is “radio-loud,” or bright at very long wavelengths. Typically, this kind of emission is expected to be generated by powerful jets that are ejected from the poles of a quasar. For example, the authors compare this radio-loud quasar to similar sources, which show significant variability in the X-ray part of the spectrum. This is a tell-tale sign that the X-ray emission is also generated by these jets (which might come out in fits and spurts and thus cause fluctuations in brightness over time).

However, when the authors examine X-ray data of RACS J0320−35 taken by the Chandra X-ray Observatory, they find surprising results. The quasar is extremely luminous in X-rays, making it one of the brightest in the early universe. But despite the fact that it pumps out a huge number of these energetic photons, it seems to preferentially emit only the lower-energy band of X-rays and completely lacks the highest-energy emission that characterizes similar sources. In technical terms, the X-ray spectrum of RACS J0320−35 is incredibly “soft.” Moreover, this X-ray emission seems to be constant on the timescale of months, though further observations will be required to test if it varies on longer timescales. Still, the softness of the spectrum and weak variability of this system mean that its X-ray emission is unlikely to be produced by a jet.

The authors carefully consider a particular variety of jet — one that is sharply angled towards us. Since quasar jets often travel at incredible speeds, the special theory of relativity kicks in and causes strange behaviors. In particular, an effect called relativistic beaming can cause a source to appear much brighter if traveling towards the observer at extremely high speeds. However, they find that although relativistic beaming can explain the mysterious X-ray properties of RACS J0320−35, such a scenario is incompatible with its observed radio emission. Moreover, a lack of gamma-ray emission and weak variability are further pieces of evidence against the jet origin of the X-ray emission.

Limits Are Meant to Be Broken

The article presents one more fascinating possibility for the origin of the X-rays in this source. Some theoretical work and simulations show that if a black hole breaks the Eddington limit and starts accreting matter at “super-Eddington rates,” the X-ray spectrum that results can be incredibly soft. The authors find excellent agreement between the observations and the predictions from a particular model that simulates a very slowly spinning black hole (see Figure 1). This scenario seems to be a promising explanation for the X-ray emission in RACS J0320−35, which is extremely exciting for several reasons.

Many astronomers are considering super-Eddington accretion to explain the masses of early quasars and their fainter counterparts, called active galactic nuclei. Because supermassive black holes are supposed to have a cap on their accretion rate (the Eddington limit), the earliest black holes in the universe should only have been able to reach large sizes after sufficient time had passed. Astonishingly, observations from JWST are finding massive active galactic nuclei everywhere in the early universe, which seems to violate this — these black holes appear astonishingly massive despite existing for only a fraction of the universe’s current age. However, if early black holes could grow faster than expected by undergoing super-Eddington accretion, this tension might be resolved.

Despite the promising initial results of this model, there are a few caveats to the results presented in today’s article. For example, the radio jets observed from this source require a rapidly spinning black hole, which conflicts with the model assumptions. The authors note that a radio jet can be very far from a black hole, tracing its past activity. In fact, this jet may have actually spun down the central supermassive black hole by extracting energy from it, a fascinating possibility that will require both further observations and simulations to explore. Today’s bite shines a brilliant light on this possibility by analyzing RACS J0320−35, a fascinating quasar in the early universe and a stunning example that cosmic limits are meant to be broken.

Original astrobite edited by Veronika Dornan.

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.

The post The Winner of the Cosmic Speed-Eating Contest appeared first on AAS Nova.

New research suggests that the mysterious “little red dots” spotted in the early universe could be supermassive black holes birthed in the collapse of dark matter halos.

Another Theory for Little Red Dots

Many theories exist for the origins of little red dots: compact, reddish objects spotted mainly in the first billion years after the Big Bang. The leading theory states that that little red dots are growing black holes encased in dense gas. The black holes at the centers of these little red dots appear to be tens or even hundreds of millions of times the mass of the Sun, raising questions about how they grew so massive so quickly. One possibility is that they started out quite massive, arising from black holes born from the collapse of massive gas clouds in the early universe.

A recent research article explores that theory, with a twist: that the black holes at the heart of little red dots were born not out of regular, baryonic matter, but out of dark matter.

A Dark (Matter) Past

In the early days of the universe, tiny fluctuations in the density of dark matter began to grow, eventually collapsing into vast spheroidal structures called dark matter halos. In the leading theory of cosmology, ΛCDM, dark matter interacts with itself and normal matter only through gravity. This leads to the creation of stable dark matter halos that act as the invisible scaffolding within which the first stars and galaxies grow.

In today’s article, Fangzhou Jiang (Peking University) and collaborators investigated the evolution of halos containing self-interacting dark matter. Particles of self-interacting dark matter, as the name suggests, can interact with one another through collisions and exchange heat. This small adjustment, sometimes invoked in alternatives to ΛCDM to explain the properties of dwarf galaxies, can lead to the collapse of dark matter halos into black holes.

Seeding Black Holes

Jiang and coauthors examined whether this process could explain the observed population of little red dots. First, the team examined whether the timescales are feasible: is it possible for dark matter to assemble itself into massive halos and collapse into black holes, all within the first billion years of the universe?

The answer appears to be yes — in this framework, dark matter halos with masses between 10^6.5 and 10^8.5 solar masses were able to form black holes between 10^4.5 and 10^6.5 solar masses by a redshift of z = 8.5, when the universe was just 600 million years old.

Jiang’s team then performed semianalytic modeling to explore how these “seed” black holes grow and evolve through accretion and mergers. This analysis generated a distribution of black hole masses consistent with what has been observed in little red dots. The team cautioned that their results are sensitive to the interaction cross-section of the dark matter particles, as well as various other parameters like the black hole accretion duty cycle. Their modeling also assumes that the halo collapse takes place before any baryonic matter collects within it. Intriguingly, the authors found that the presence of baryons accelerates the collapse of the dark matter halo, speeding the seeding process.

To close, Jiang and collaborators noted that this process is not mutually exclusive with other black hole seeding mechanisms, and as studies of self-interacting dark matter continue, its ability to create black holes in the early universe should be examined further.

Citation

“Formation of the Little Red Dots from the Core Collapse of Self-Interacting Dark Matter Halos,” Fangzhou Jiang et al 2026 ApJL 996 L19. doi:10.3847/2041-8213/ae247a

The post A Dark Matter Origin for Little Red Dots 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 Fate of EMRI-IMRI Pairs in Active Galactic Nucleus Accretion Disks: Hydrodynamical and Three-body Simulations
Authors: Peng Peng et al.
First Author’s Institution: Peking University
Status: Published in ApJ

Active galactic nuclei (AGNs) are the extremely luminous central regions of some galaxies, powered by gas accreting onto their supermassive black holes and often outshining the entire galaxy in which they reside. One reason they are so studied in astronomy is that they connect many pieces of physics and astronomy in one cosmic place. This is especially true for AGNs as potential gravitational wave sources. Gravitational waves are observed when two compact objects, usually black holes, orbit each other. Black holes span a massive range of masses, but they are typically categorized into one of three categories: stellar-mass black holes, or sBHs (tens to hundreds of times the mass of the Sun), intermediate-mass black holes or IMBHs (hundreds to thousands of times the mass of the Sun), and supermassive black holes or SMBHs (millions to billions of times the mass of the Sun). AGNs are special because they are among the very few places where black holes across this entire mass spectrum might be found in the same place at the same time. Not only do they host SMBHs at their centers, but their gas disks are ideal nurseries for capturing and growing sBHs and IMBHs.

Current-generation gravitational wave detectors like the LIGO–Virgo–KAGRA (LVK) network can observe stellar-mass to lite-IMBH black hole mergers. Future detectors like the Laser Interferometer Space Antenna (LISA) will be able to observe black holes in the intermediate-mass to supermassive mass range. In addition to the mass range a detector can detect, it is also valuable to know the mass ratio (usually denoted by q) that a detector might detect. Unequal-mass-ratio mergers can tell us a lot about general relativity that more equal-mass mergers cannot because the smaller object orbits the more massive one many times right before the merger, essentially providing a gravitational wave measurement of spacetime around the larger black hole. (See this video for an example of black hole orbits with a large mass ratio, and imagine the spacetime observations around the larger black hole that could be possible with orbits like that.)

One of the most promising advances in gravitational wave detection with LISA will come with the observation of extreme-mass-ratio inspirals (EMRIs), usually defined as involving a smaller black hole that is at least 10,000 times less massive than the massive black hole it orbits (though the exact mass ratio defining an EMRI is a matter of convention and may vary somewhat). In addition, LISA will be able to observe intermediate-mass-ratio inspirals (IMRIs), usually defined as when the smaller black hole is 100–10,000 times less massive than the larger one.

This article uses multiple techniques to address the question of what happens when an AGN disk hosts both an IMBH and an sBH at the same time. The authors began with a hydrodynamic simulation of an AGN gas disk around a 10⁶-solar-mass SMBH. They add a 10³-solar-mass IMBH into the gas disk. Because the IMBH orbits within a gas disk, the gas exerts a force on it, causing its orbit to shrink toward the SMBH (a process called migration). Additionally, the IMBH carves out a path through the gas. Once the IMBH carves out enough of a path in the gas, the authors add an sBH of 20 solar masses into the simulation near the IMBH.

The authors test the sBH outcome for two initial conditions of the gas disk. The first, which I will refer to as “InnerDisk,” is when gas already exists inside the IMBH’s orbit (see Figure 1). The other, which I will refer to as “NoInnerDisk,” is when the simulation begins with gas only outside the IMBHs orbit, with no gas initially between the IMBH and SMBH. In this case, gas crosses the IMBH’s gap after the simulation starts. In the InnerDisk case, the sBH initially gets pushed inward from the presence of the inner gas, but that gas steadily drains into the SMBH and is only partly refilled, so the gas’s push on the sBH weakens over time. In the NoInnerDisk case, the IMBH’s direct pull on the sBH becomes more important. The amount of gas that leaks across the IMBH orbit into the inner disk gradually settles into a steady state that is less dense than the InnerDisk case. With a weaker gas push, the sBH stays closely tied to the IMBH and migrates inward at nearly the same rate. In both setups, the IMBH carves a gap in the gas and keeps moving inward, but the presence and evolution of inner gas chiefly determine how closely the sBH can keep up.

Once the sBH and IMBH migrate close enough to the SMBH, gravitational waves are responsible for more and more of the energy loss and orbital decay of the system compared to the gas. To account for that, once the sBH and IMBH migrate close enough to the SMBH, instead of using a hydrodynamic simulation of a gas disk, the authors switch over to a “three-body problem” solver. Because these are black holes emitting gravitational waves, regular old Newtonian mechanics is insufficient, so they add post-Newtonian terms to correct for this. Additionally, though they no longer model the gas hydrodynamically, they do include terms for a gas “force” acting on the black holes to mimic the gas disk.

Once the IMBH and sBH were in the gravitational regime, their outcomes became much more chaotic. As seen in Figure 2, a slight change in the initial phase angle of the sBH can lead to drastically different consequences for the system. In some cases, the sBH is ejected entirely. In other instances, it merges with the IMBH soon after the simulation begins. Yet in others, it first merges with the SMBH. This leads to one overall message of this article: the orbits of the IMBH and sBH tend to be regular with some gentle variation when they are farther out in the gas disk, but they become highly chaotic once they shrink into the gravitational wave regime closer to the central SMBH.

AGN disks may provide a natural setting for interactions among stellar-mass, intermediate-mass, and supermassive black holes. The authors of this article demonstrated that gas can keep an IMBH and an inner sBH migrating together until gravitational waves dominate, after which slight differences in their orbital phases can lead to a wide range of outcomes. While uncertainties remain, this study provides more evidence that LISA could identify. Until LISA flies, continued simulations like this one will help refine the spectrum of EMRIs and IMRIs we can expect to see.

Original astrobite edited by Maggie Verrico.

About the author, William Smith:

Bill is a graduate student in the astrophysics program at Vanderbilt University. He studies gravitational wave populations with a focus on how these populations can help inform cosmology as part of the LIGO Scientific Collaboration. Outside of astrophysics, he also enjoys swimming semi-competitively, music and dancing, cooking, and making the academy a better place for people to live and work.

The post The Black Hole Meetup: EMRIs and IMRIs in the Same Active Galactic Nucleus Disk 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 Discovery of Little Red Dots in the Local Universe: Signatures of Cool Gas Envelopes
Authors: Xiaojing Lin et al.
First Author’s Institution: Tsinghua University and University of Arizona
Status: Published in ApJ

Astronomers are using JWST to search the early universe for strange and captivating objects, and the results so far have exceeded all expectations. For every question we definitively answer, several deeper ones seem to emerge. The study of active galactic nuclei (AGNs), black holes that are actively consuming matter at the centers of galaxies across the universe, is no exception. Our pre-JWST understanding of AGNs has been completely shattered by the discovery of an astounding population of objects called little red dots (LRDs).

We know these objects host active black holes for several reasons. For one, they’re incredibly small despite being extremely energetic (that’s the “little” in their name). The smallest LRD we’ve seen appears to be less than 100 light-years across — for reference, the nearest star to the Sun is 4 light-years away — and yet is still as bright as a galaxy. The most plausible explanation for such brightness and compactness is a supermassive black hole that’s actively consuming matter. As further evidence for this hypothesis, we observe broad Balmer emission lines, spectral features that serve as a clear signature of AGN activity, in the vast majority of LRDs.

However, that’s where the similarities between LRDs and more typical AGNs seem to end. First off, astronomers have been unable to detect any significant X-ray emission from LRDs. This is shocking, since X-rays are a telltale signature of previously known AGNs. Another classic way to identify AGNs is by looking for changes in their brightness over time, since they can show drastic variability in their emission on the scale of years or even days. LRDs buck the trend by showing little to no fluctuation. Other classic AGN signatures that LRDs lack include radio emission and an abundance of hot dust. Explaining all of these unusual features has been incredibly challenging; nevertheless, coming up with a solution is crucial because there appear to be orders of magnitude more LRDs than any other kind of AGN in the early universe!

Wishing on a Star

One leading explanation for LRDs has recently gained significant traction. The hypothesis suggests that early black holes may have been cocooned in shrouds of extremely dense gas. This scenario helps explain the absence of many typical AGN signatures in LRDs. For example, this dense gas could absorb the X-rays generated by the central black hole. The gas-enshrouded model also explains a particular feature in the spectra of many LRDs known as a Balmer break. This feature is usually interpreted as coming from old stars with relatively cool atmospheres. The cocooned AGN hypothesis implies that Balmer breaks could actually be made by a black hole embedded in a cloud of gas, which somewhat resembles an enormous star!

This model helps explain the properties of some puzzling LRDs, including the most distant one we currently know of. However, their enormous distance makes them difficult to study in detail. It would be much easier to examine LRDs if they existed in the nearby universe, since they would appear much brighter and we could probe them on small spatial scales. Unfortunately, previous studies with JWST suggest that LRDs started becoming a lot less common around 12 billion years ago (corresponding to a redshift of about z = 4).

Luckily, less common doesn’t mean extinct! The authors of today’s article leverage data from the Sloan Digital Sky Survey (SDSS), which has taken millions of spectra of objects across the night sky over the past few decades. By mining this rich and diverse dataset, they identify a handful of LRDs in the nearby universe. Although they’re still far beyond our own Local Group, they’re practically in our backyard compared to the distant LRDs we’ve seen before. The authors followed up the new sources with some of the most powerful ground-based telescopes, enabling a detailed study of their properties.

A Chick That Forgot to Hatch

The first major result is that these local LRDs really do resemble many of the distant ones identified by JWST. They show a characteristic “V”-shaped spectrum in the ultraviolet and visible, a key feature in the definition of LRDs. They’re also quite compact. Using existing data from the Hubble Space Telescope, the authors measured the size of one source and found a tiny core embedded within a galaxy only a few thousand light-years across. For comparison, the Milky Way spans about 100,000 light-years.

Using spectroscopy from the Large Binocular Telescope, one of the Magellan Telescopes, and the MMT (formerly Multiple Mirror Telescope), the authors of this article find a rich variety of spectral features. This is where the proximity of these objects is extremely important. Taking spectra of the distant LRDs in this astounding level of detail would be at best prohibitively expensive (multiple full days of JWST observations) and at worst be completely impossible. In contrast, the nearby LRDs appear much brighter than their distant cousins. Their spectra are like intricate tapestries, with each thread revealing new details about their properties.

The authors find numerous broadened emission lines, signaling the presence of an active black hole. They also detect several intriguing absorption lines. These are most striking in one source, J1025+1402, nicknamed “The Egg.” In this object, there are clear absorption features from sodium, potassium, iron, and calcium. These elements appear in the observed states only under specific physical conditions. The authors interpret these findings as implying the presence of an envelope of cool gas surrounding the central black hole (see Figure 1). Such a scenario closely resembles the gas-cocooned AGN model proposed to explain distant LRDs!

These observations provide direct evidence for a potentially new kind of AGN. These local objects do differ slightly from their more distant counterparts; for example, they show some emission from hot dust, which is absent in early LRDs. Still, this adds another piece to the puzzle of this cosmic mystery. The authors hope that future observations will further illuminate the inner workings of LRDs across cosmic time. For example, studies may reveal what objects “hatch” from a source like the Egg, offering new insight into the life cycles of these unusual AGNs.

Original astrobite edited by Niloofar Sharei.

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.

The post A Black Hole Egg That Forgot to Hatch appeared first on AAS Nova.

The gravitational wave background — the constant, low-frequency hum of colliding supermassive black holes across the universe — seems to have a larger amplitude than expected. Can preferential accretion explain why?

Larger than Expected

In 2023, researchers announced the discovery of compelling evidence for the gravitational wave background: a low-frequency, low-amplitude signal that is likely due to supermassive black hole binaries across the universe steadily trundling toward mergers. The amplitude of the background, however, is larger than expected for a population of merging supermassive black holes.

Though some researchers have invoked new physics to explain this discrepancy, all that may be required is an adjustment to our understanding of the supermassive black hole binary population in our universe. In a recent research article, Julia Comerford (University of Colorado Boulder) and Joseph Simon (University of Colorado Boulder; Oregon State University) tackled one of the underlying assumptions about the masses of merging supermassive black holes.

Preferential Accretion Pathway

When supermassive black holes merge, the strength of the gravitational wave signal depends on how similar the black holes were in mass; merging equal-mass black holes produce stronger signals than mismatched black holes do. What if, Comerford and Simon proposed, the masses of merging supermassive black holes scattered across the universe are more similar than previously thought?

Observations and simulations of supermassive black holes within colliding galaxies appear to support this hypothesis. Rather than staying the same mass as they approach one another, as models tend to assume, supermassive black holes likely gather material from their surroundings and gain mass.

What’s more, it appears that the smaller of the two black holes tends to pack on more mass, meaning that the masses of the black holes grow more similar as they wind toward a merger. (This somewhat counterintuitive result arises because the smaller of the two black holes encounters more gas as it spirals inward.)

Boosting the Signal

If accretion tends to even out the masses of the binary members, is the resulting increase in signal strength large enough to explain the observed amplitude of the gravitational wave background?

Comerford and Simon modeled the gravitational wave background from supermassive black hole binaries undergoing preferential accretion onto the smaller black hole. Benchmarking their model with observations wherever possible, they found that just a 10% increase in the total mass of the merging black holes can raise the gravitational wave background to the median observed value — easing the discrepancy without the need for speculative new physics.

The signal-boosting effect from preferential accretion may be especially important if the binary evolution timescale — the time it takes for black holes approaching a merger to reach a separation at which their gravitational waves become accessible to pulsar timing arrays — is longer than the estimated 1.8 billion years. At longer timescales, models without this accretion become entirely inconsistent with observations. Future research that examines the masses and accretion rates of supermassive black holes as they approach make their way toward a merger can provide further clues to the role of preferential accretion.

Citation

“Preferential Accretion onto the Secondary Black Hole Strengthens Gravitational-Wave Signals,” Julia M. Comerford and Joseph Simon 2025 ApJ 994 168. doi:10.3847/1538-4357/ae1133

The post Boosting the Gravitational Wave Background appeared first on AAS Nova.

What if there was one process capable of creating every type of detectable stellar-mass black hole system? Recent research suggests there might be, and that it involves a triple-star system.

Three Separate Contexts

Stellar-mass black holes, or black holes that are at most a few hundred times the mass of the Sun, pop up in a number of different environments in the Milky Way. Astronomers have known since the 1960s that these black holes are the engines behind accreting low-mass X-ray binaries; more recently, researchers at gravitational wave observatories such as LIGO have found pairs of black holes orbiting each other just prior to merging; and, in just the past few years, scientists using the Gaia spacecraft have found black holes on wide, prowling orbits around still-burning stars.

Although each of these scenarios involves a black hole, it’s unclear how exactly these black holes are related to one another, or if they’re related at all. For instance, do low-mass X-ray binaries form the same way as the binary black holes observed with LIGO? Are the wide star–black hole binaries discovered by Gaia destined to eventually merge as two black holes, or are they a separate population altogether?

Recent research led by Smadar Naoz (University of California, Los Angeles) offers a potential answer to this question of relatedness — that each of these situations forms through the same underlying process.

Triples Systems

The mechanism Naoz and collaborators describe would work as follows. First, three stars begin their lives all bound together via gravity. Two of these stars orbit each other fairly closely, but the third hangs back much farther away. After the two inner stars burn out and collapse into black holes, they undergo the kind of collision commonly observed by LIGO and merge together. This process gives the resulting larger black hole a “kick,” meaning it goes flying off away from the site of the impact with some new velocity.

What happens next depends on the geometry of the system and the direction of the kick. If the remnant black hole gets shot away from the third star, it might just drift off on its own and leave the star behind. If the kick isn’t too strong, the remnant will remain gravitationally bound to that third star, and the system will eventually look like the star–black hole pairs observed by Gaia. Finally, if the kick sends the remnant toward the third star, some dramatic outcomes become possible: either the black hole starts nibbling on the star and the system becomes a low-mass X-ray binary, or the black hole simply smashes into the star, destroying it completely in a large, flashy explosion paired with a gravitational wave signal.

The authors stress that this mechanism is almost certainly not the only way that these three stellar-mass black hole systems form. However, it is exciting to consider a common thread underlying such seemingly different scenarios, and with upgrades coming to gravitational wave observatories, we can hope for tests of its feasibility in the near future.

Citation

“Triples as Links Between Binary Black Hole Mergers, Their Electromagnetic Counterparts, and Galactic Black Holes,” Smadar Naoz et al 2025 ApJL 992 L12. doi:10.3847/2041-8213/ae0a20

The post Black Holes with a Shared Background appeared first on AAS Nova.

Meet GW241011 and GW241101, two events from the fourth observing run of the LIGO, Virgo, and KAGRA (LVK) gravitational wave detectors. With rapid spins and mismatched black hole masses, both events provide strong evidence for black hole growth through hierarchical mergers.

A Decade of Discovery

Humanity is 10 years into its study of the gravitational wave universe, and detectors across the globe are about to wrap up their fourth observing run. The recently released fourth catalog of gravitational wave transients, GWTC-4.0, more than doubles the number of recorded events.

Today, we’re taking a look at two of the fourth observing run’s gravitational wave events, both of which point to black holes born in dense environments.

Two Detections in the Spotlight

GW241011 and GW241101 are gravitational wave signals that reached Earth in late 2024. Using Bayesian parameter estimation, members of the LVK collaboration determined that each of these two signals arose from the merger of a pair of black holes.

Though the LVK detectors have by now spotted dozens of coalescing black hole pairs, these two detections stand out. GW241011 is the third-loudest gravitational wave signal ever detected, and its primary (i.e., more massive) black hole has one of the largest and most precisely measured spins among black holes detected via gravitational waves.

GW241101 flips the script: its primary black hole also spins rapidly, but it appears to do so in a direction opposite from the direction in which the black holes orbit. Though its spin isn’t measured as precisely as that of the primary black hole in GW241011, this event still provides the best evidence so far that the spins of some merging black holes are misaligned with their orbital motion.

In addition to their standout spin parameters, these events are also remarkable for the masses involved. In both cases, the larger black hole has a mass of 15–20 solar masses, and the smaller black hole is significantly smaller — about 6 solar masses for GW241011 and 8 solar masses for GW241101.

A Black Hole Genealogy Project

The rapid spins and comparatively large masses of the primary black holes of GW241011 and GW241101 don’t line up with what’s expected for black holes arising in isolated binary systems, unsubjected to outside influences. But they do match expectations for hierarchical mergers, in which one or more of the black holes involved is itself the product of a merger.

If these signals arose from hierarchical mergers, that tells us something about the environment in which the black holes lived. When two black holes merge, the product is expected to spin rapidly and receive a “kick.” For a black hole pair in a loose grouping of stars, this kick would likely boot the merger product out of the group, preventing it from encountering other black holes and merging again.

But in dense environments like compact star clusters, even a good strong kick isn’t enough to overcome the cluster’s escape velocity and launch the resulting black hole on a lonely journey through space. Instead, these black holes are retained in the dense cluster environments of their birth, where they may dance and merge with another black hole partner. While it’s not possible to entirely rule out other origins, such as an isolated pair of massive binary stars, the data strongly support the hierarchical merger scenario.

This discovery yet again demonstrates the ability of our gravitational wave detectors to reveal the lives and histories of black holes throughout our universe. Stay tuned for even more black hole news from the current observing run!

Citation

GW241011 and GW241110: Exploring Binary Formation and Fundamental Physics with Asymmetric, High-Spin Black Hole Coalescences,” A. G. Abac et al 2025 ApJL 993 L21. doi:10.3847/2041-8213/ae0d54

The post Not Their First Rodeo: Gravitational Wave Detectors Spot Merging Black Holes That Have Merged Before appeared first on AAS Nova.

Catastrophic encounters between stars and massive black holes usually take place in the nuclei of galaxies, but not always. Researchers recently reported on the brightest-ever radio emission from an off-nuclear tidal disruption event caused by a wandering or recoiling black hole.

Signature of a Roaming Black Hole

Tidal disruption events occur when a star ventures too close to a massive black hole. The tidal forces of the black hole stretch the star until it’s partially or entirely disrupted, sometimes causing jets or outflows to spray from the shredded star. One thing that often distinguishes a tidal disruption event from the sea of other possible transients is the location, close to the nucleus of a galaxy.

But not all tidal disruption events happen in the center of a galaxy. In rare cases, a massive black hole roaming elsewhere in a galaxy may encounter a star, sending out a tell-tale signal in an unexpected location.

One such event is AT 2024tvd, which was discovered at optical wavelengths by the Zwicky Transient Facility. Though the initial identification placed it at the center of its host galaxy, follow-up observations suggested that it was in fact 2,600 light years from the center. What can radio observations tell us about this rare off-center event?

Radio Reconnaissance

Less than three months after AT 2024tvd was discovered, Itai Sfaradi (University of California, Berkeley) and collaborators launched a months-long radio-wavelength observing campaign using the Very Large Array, the Atacama Large Millimeter/submillimeter Array, the Arcminute Microkelvin Imager Large Array, the Allen Telescope Array, and the Submillimeter Array. Radio observations are critical for investigating jets and outflows from tidal disruption events.

The observations, which spanned centimeter and millimeter wavelengths, revealed two emission peaks from the tidal disruption event. The first peak occurred roughly 131 days after the event was discovered, and the second followed at day 194.

About 40% of the tidal disruption events that have been identified at optical wavelengths show this kind of delayed brightening at radio wavelengths, but AT 2024tvd stands out as having the fastest radio evolution ever seen. Even among fairly fast-evolving flares, AT 2024tvd is unusual, having a brighter second peak than peer events.

Prompt or Delayed, Outflow or Jet?

To understand the origin of the fast-evolving, extremely bright radio emission from AT 2024tvd, Sfaradi’s team modeled the emission that would arise from outflows and jets. For both wide-angle outflows and narrow jets, the team considered both prompt — arising simultaneously with the event’s optical detection — and delayed sources.

The team’s modeling highlighted several possible scenarios. In the first, both bright radio peaks arose from a single outflow that was launched about 84 days after the star met its doom. The double-peaked behavior is due to the outflow interacting with a complex distribution of material surrounding the black hole. It’s also possible for the two peaks to arise from separate outflows or jets, one launched around 84 days and the other around either 170 or 190 days, depending on whether the second source is a mildly relativistic outflow or a relativistic jet.

Sfaradi and collaborators posited that AT 2024tvd’s unusual radio behavior could be due to its off-nuclear location, but they acknowledged that this event might simply occupy a region of tidal disruption event parameter space that had yet to be explored. Sensitive interferometric or polarimetric observations may reveal more about how AT 2024tvd interacts with its environment, helping to illuminate the nature of this rare event.

Citation

“The First Radio-Bright Off-Nuclear TDE 2024tvd Reveals the Fastest-Evolving Double-Peaked Radio Emission,” Itai Sfaradi et al 2025 ApJL 992 L18. doi:10.3847/2041-8213/ae0a26

The post Investigation of the First Radio-Bright Off-Nuclear Tidal Disruption Event appeared first on AAS Nova.

With very small stellar masses and tiny radii, ultracompact dwarf galaxies raise questions about the dividing line between the highest-mass star clusters and the lowest-mass galaxies. A recently published article leverages JWST’s high resolution to target one tiny galaxy and investigate its origins.

Origins of Ultracompact Dwarf Galaxies

How tiny can a galaxy get? Discovered 20 years ago among the dense environments of the Virgo and Fornax clusters, ultracompact dwarf galaxies walk the line between the largest globular clusters and the smallest galaxies. Determining if these dwarfs are stellar in nature or actually of galactic origin is complex, but one sure way to get at this question is to determine if an ultracompact dwarf galaxy houses a supermassive central black hole. 

While astronomers have identified hundreds of these tiny dense galaxies, supermassive black holes have been detected in only five. Hoping to extend this sample, Matthew Taylor (University of Calgary) and collaborators targeted UCD 736, an ultracompact dwarf galaxy located in the Virgo galaxy cluster. If a massive black hole is found in this galaxy, it will be the smallest and least luminous ultracompact dwarf to have such a detection. Exploring galaxies at such small sizes will allow researchers to determine what fraction of ultracompact dwarfs have galactic or star cluster origins, which can provide insights into massive black hole seeding mechanisms in the early universe.

Modeling Black Hole Mass

In order to search for a central black hole in UCD 736, Taylor and team obtained high-resolution spectroscopy from JWST and supplemental imaging from the Hubble Space Telescope. The authors used the stellar kinematics and light profile of the galaxy to estimate the mass of its central black hole with three independent modeling methods. Based on the expected impacts of a massive black hole on galaxy dynamics and the estimated stellar population of the galaxy, the authors found that UCD 736 likely hosts a central supermassive black hole with mass ~2.1 million times the mass of the Sun. 

However, the authors noted that the three models do not provide equivalent confidence levels in this estimate — while one model confidently rules out the possibility of no central black hole at 3σ significance, the other two models were less constraining, ruling out the possibility of there not being a black hole to only 1σ. Despite these differences, all three models agree on the central black hole mass within the first confidence interval, indicating a positive detection of a black hole in UCD 736.

Progenitor of UCD 736

From their observations and modeling, the authors presented the fifth positive detection of an ultracompact dwarf galaxy with a central supermassive black hole within the Virgo Cluster. Given the presence of this black hole, UCD 736 likely originated as a more massive galaxy that was tidally stripped as it interacted with other nearby cluster galaxies. Interestingly, though, other ultracompact dwarf galaxies with black hole detections in the Virgo Cluster are much closer to the massive galaxy that likely stripped them. UCD 736 sits about 160,000 light-years outside of the nearest giant galaxy Messier 59’s tidal radius, which does not rule out interactions but could indicate that Messier 59 is particularly good at stripping material from smaller galaxies. 

Continued searches for black holes in ultracompact dwarfs will further probe the differences between the highest-mass globular clusters and the lowest-mass galaxies. Revealing more within this parameter space will allow astronomers to test black hole seeding and galaxy formation theories.

Citation

“A Supermassive Black Hole in a Diminutive Ultracompact Dwarf Galaxy Discovered with JWST/NIRSpec+IFU,” Matthew A. Taylor et al 2025 ApJ 991 L24. doi:10.3847/2041-8213/ae028e

The post Supermassive Black Hole in a Super Tiny Galaxy Found with JWST appeared first on AAS Nova.