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

Red Dot, Blue Dot

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

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

Baggen and coauthors investigated whether the ultraviolet radiation from the blue companions is strong enough to have triggered this transformation. The team used spectral energy distribution modeling to determine the luminosities of the blue companions from 91.2 to 111 nanometers. This analysis showed that the radiation from the blue companions is equal to or greater than the threshold necessary to encourage the direct collapse of a gas cloud into a massive compact object.

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

Little Red Dots as Young Globular Clusters

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

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

To do this, the team propagated the observed mass function of little red dots at a redshift of z = 7 forward in time to z = 0. This process accounted for the rapid evolution of the supermassive star into a black hole, as well as the evolution of and feedback from the massive stars in the cluster. Comparing the resulting mass function to the population of present-day globular clusters, the team found that the mass functions had very similar shapes, and the number densities of little red dots and globular clusters in the present day are estimated to be of the same order of magnitude: 0.1–0.3 Mpc^-3 and 0.8 Mpc^-3, respectively.

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

Citation

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

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

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

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

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

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

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

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

Intermediate Mass, Impossible Difficulty

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

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

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

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

Putting Faint AGNs Under a Lens

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

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

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

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

Because the AGNs analyzed in today’s article host central black holes with much lower masses than any that have been observed in the past (at this early time in the universe), the authors are able to probe a completely new region of the black hole mass function. As seen in Figure 1, the leftmost red hexagon (lowest-mass data point) deviates from the roughly straight line traced by the other data points. This suggests that there are substantially more black holes with a few hundred thousand solar masses than previously expected.

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

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

Original astrobite edited by Tori Bonidie.

About the author, Ansh Gupta:

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

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One of the most luminous supergiant stars in the Andromeda Galaxy, M31-2014-DS1, has disappeared, potentially leaving behind a black hole shrouded in dusty gas. What do new infrared and X-ray observations tell us about this event?

Failure to Explode?

Massive stars are famous for going out with a bang. After swelling into supergiants, these stars bring their brief lives to a close in a cosmic fireworks show: a supernova explosion that creates a neutron star or a black hole.

But a splashy supernova explosion may not be the only way for a massive star to go out. As observations have begun to suggest, some massive stars may — for reasons not yet fully understood — quietly collapse in upon themselves, going out with a whimper rather than a bang. Though less spectacular and far harder to spot, these “failed” supernovae highlight a possible pathway for the formation of stellar-mass black holes.

A Newborn Black Hole in a Dense, Dusty Blanket

Just last month, researchers reported their discovery of a potential failed supernova. The supergiant M31-2014-DS1 suddenly brightened in 2014 before fading to obscurity, leading researchers to suspect that the star had experienced a failed supernova and created a black hole. The event shared similarities with another failed supernova candidate, NGC6946-BH1.

In a new article published in the Astrophysical Journal Letters, Kishalay De (Columbia University; Flatiron Institute) and coauthors have used JWST and the Chandra X-ray Observatory to learn more about what remained after M31-2014-DS1 disappeared. The JWST observations show an extremely red object that has faded considerably in just a few years, with a deep absorption feature from silicate dust and numerous narrow molecular absorption lines. Chandra did not detect any X-rays.

Together, these observations support a model in which the collapsing star ejected its outer layers in a relatively low-energy event (somewhere in the broad ballpark of one hundred-millionth to one ten-thousandth the energy of a typical core-collapse supernova) and formed a black hole. Some of the ejected material fell backward and fed the newborn black hole, while the remainder created a dense blanket that blocked the light from the accreting black hole from view.

Continued Evolution

In observations from 2024, the source had faded to just 7% of the progenitor star’s luminosity, supporting the conclusion that the star has disappeared and what lies beneath the dusty ejecta is a black hole. De’s team expects that as time goes on, the gas that obscures the accretion-powered luminosity of the newborn black hole will expand and become less dense along our line of sight. At some point — estimated to be no sooner than about 27 years from now — the X-ray emission from the accreting black hole should pierce the dusty shroud and become visible to sensitive X-ray observatories. In the infrared, JWST will be able to track the source’s evolution caused by continued dust creation in the expanding shell.

Thanks to its location in a neighboring galaxy, M31-2014-DS1 has granted astronomers a front-row seat to a poorly understood pathway for black hole formation. Going forward, we can expect further insights into M31-2014-DS1 and, hopefully, the discovery of many more sources like it.

Citation

“Fading into Darkness: A Weak Mass Ejection and Low-Efficiency Fallback Accompanying Black Hole Formation in M31-2014-DS1,” Kishalay De et al 2026 ApJL 999 L25. doi:10.3847/2041-8213/ae468d

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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

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

Title: Massive Black Hole Seed Formation in Strong X-Ray Environments at High Redshift
Authors: Kazutaka Kimura, Kohei Inayoshi, and Kazuyuki Omukai
First Author’s Institution: Tohoku University
Status: Published in ApJ

Environments of Massive Black Holes

Astronomers have found that nearly every observable galaxy hosts a central supermassive black hole (SMBH) — a black hole more than a million times more massive than the Sun. Using JWST, they have peered back into the early universe to observe some of the earliest galaxies, and these early galaxies also contain SMBHs. In fact, many of these galaxies seem to contain SMBHs that are more massive than we expected them to be this early in the universe.

We believe that most black holes form at the ends of the lives of massive stars, which collapse under their own gravity when they run out of fuel. We expect that this happened to the first stars too, forming “light” (as in “lightweight”) seeds of SMBHs with masses up to about 100 solar masses. Astronomers also think that the right conditions in the early universe could lead to the formation of a “heavy” seed with a mass on the order of 10⁴ solar masses or more; this kind of black hole is called a direct-collapse black hole (DCBH).

In order to form a DCBH, a gas cloud needs to collapse without fragmenting to form star clusters and stars — if stars form, there won’t be enough mass funneled to the center of the cloud to form the DCBH. One important criterion for this to happen is the absence of coolants, like metals and molecular hydrogen (H₂), which cause fragmentation. One way to eliminate H₂ is with a particular type of ultraviolet light called Lyman-Werner radiation, which can destroy H₂ molecules. However, recent results from the Hydrogen Epoch of Reionization Array (HERA) suggest that early galaxies emitted more X-rays than expected, which would increase the amount of H₂ and make it less likely for DCBHs to occur. Today’s authors investigate the feasibility of forming DCBHs in these X-ray-bright environments.

Modeling Black Hole Formation

Today’s authors model the collapse of gas in dark-matter halos that have a nearby neighboring halo. This neighboring halo emits radiation like ultraviolet light and X-rays that impact the formation of molecules like H₂, which affects the gas chemistry. This radiation is typically emitted by hot gas in star-forming regions. The authors also track quantities like the gas density and temperature as the gas collapses. Once the gas collapses enough, a star forms at the center and continues to accrete surrounding material. Once this star evolves and reaches the end of its life, it becomes a black hole.

The authors considered different intensities of X-ray radiation relative to a critical value of Lyman-Werner radiation believed to destroy enough H₂ to form a DCBH, which is called J₂₁. They explore values of the X-ray intensity J_x relative to J₂₁, considering ratios of 0, 10^-6, 10^-5, and 10^-4.

Another important consideration was the baryonic streaming velocity. This is the relative bulk velocity between baryonic (i.e., “normal”) matter and dark matter in the early universe. Higher streaming velocities can delay the collapse of gas in dark-matter halos, which affect gas properties like density, temperature, and chemistry. The streaming velocity depends on the redshift, z, which is given by σ_bsm = 30 km/s (1+z)/(1+z₀), where z₀ = 1,100. This “standard” relationship has been calibrated with measurements from observations. The authors consider two cases for the streaming velocity: v_bsm = 0 and v_bsm = 1σ_bsm, which are denoted in the figures below.

X-Rays and Seed Suppression

The first main results are shown in Figure 1. The authors find that a large number of intermediate-mass seeds form from H₂ cooling, shown in blue, regardless of the X-ray intensity. A smaller number of higher-mass seeds form from H–H₂ and H–H cooling, but these cooling processes become suppressed as the X-ray intensity increases. This is because the increased X-ray intensity converts more H to H₂. Interestingly, accounting for the streaming velocity all but wipes out black hole formation via H₂ cooling except at very high X-ray intensities.

Another main set of results are the black hole mass functions (that is, the number density of black holes for a given black hole mass), shown in Figure 2. Note that this differs from Figure 1 because we are now accounting for the number density of black holes, not just the number, and we are no longer categorizing black holes based on their cooling mechanism. As before, we see that most massive black holes are eliminated with a high X-ray intensity and no streaming velocity, but a higher streaming velocity tends to produce more massive black holes regardless of the X-ray intensity. These black hole mass functions provide a useful comparison to observational results from telescopes like JWST. In summary, today’s authors find that a high X-ray intensity leads to less-massive black holes due to the increased amount of H₂, but accounting for the baryonic streaming velocity can produce massive black holes even with a large amount of X-rays. The number densities of these black holes appear to agree with observations from JWST, meaning that this could be a promising formation mechanism for the observed SMBHs in the early universe.

Original astrobite edited by Sparrow Roch.

About the author, Brandon Pries:

I am a graduate student in physics at Georgia Institute of Technology (Georgia Tech). I do research in computational astrophysics with John Wise, using machine learning to study the formation and evolution of supermassive black holes in the early universe. I’ve also done extensive research with the IceCube Collaboration as an undergraduate at Michigan State University, studying applications of neural networks to event reconstructions and searching for signals of neutrinos from dark matter annihilation.

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