A study in The Astrophysical Journal Letters reports that a vast starless cavity in the distant galaxy Abell 402-BCG may have been carved by an ultramassive black hole pair with a combined mass near 60 billion suns. The primary study, led by Michael McDonald of MIT, uses observations from the James Webb Space Telescope and the Very Large Telescope to explain a strange dark gap at the galaxy’s center.
The gap stretches about 3,200 light-years across. It sits in the heart of a giant elliptical galaxy inside the galaxy cluster Abell 402, billions of light-years from Earth. Earlier observations had made the feature look like a patch of darkness, the kind astronomers often connect with dust blocking starlight.
Newer data point to a more dramatic scene. The center of Abell 402-BCG appears to contain a real shortage of stars, possibly created as two huge black holes spiraled around each other and flung stars away. If confirmed, the system would rank among the most massive black hole binaries ever identified.
A 3,200-light-year cavity with almost no stars
The strange cavity first drew attention because the middle of Abell 402-BCG looked oddly empty. Giant elliptical galaxies usually glow with huge numbers of old stars packed toward their centers. In this case, a central region roughly 3,200 light-years wide appears dim across a broad area.
In the new analysis, researchers estimate that the missing material amounts to about 2 billion solar masses in stars. That is a small share of the galaxy’s full stellar mass. Still, inside a central region of this size, the deficit is large enough to demand a powerful explanation.
The study focuses on a galaxy known as the brightest cluster galaxy in Abell 402. These galaxies often sit near the gravitational center of galaxy clusters. They grow through repeated collisions and mergers, which makes them natural places to search for the aftermath of black hole encounters.
At the heart of the finding is a simple question with huge implications. What could remove so many stars from the middle of a galaxy? The answer suggested by the team involves ultramassive black holes, objects so heavy that their gravitational influence can reshape an entire galactic core.
Webb helped rule out dust
Dust was the first obvious suspect. Clouds of dust are common in galaxies and they can make bright regions look dark by absorbing visible light. A galaxy’s center can contain gas, dust, old stars and active black holes in the same crowded zone.
The James Webb Space Telescope changed the test. Webb sees the universe in infrared light, which passes through dust more easily than visible light. If the dark patch were mainly caused by dust, the cavity should have looked less dark in Webb’s near-infrared observations.
Instead, the cavity stayed dark. That consistency helped the team conclude that the region has a genuine shortage of stars. The finding gave astronomers a cleaner view of the galaxy’s structure and made the black hole explanation much stronger.
Webb’s view also helped identify a compact infrared-bright source on one side of the cavity. Its light is consistent with material falling toward a black hole. When gas and dust heat up near a black hole, they can shine brightly before crossing the point of no return.
This kind of observation is especially valuable because black holes themselves emit no light. Astronomers find them by watching the matter around them and the way their gravity affects nearby stars, gas and light.
Two active black holes at the edges
A second instrument added another important clue. Using the MUSE spectrograph on the Very Large Telescope at the European Southern Observatory, the researchers found a separate source of ionized gas on the opposite side of the cavity.
That second source fits the picture of another active black hole. Together, the two sources sit on opposite sides of the star-poor gap. This layout is exactly the kind of arrangement astronomers would look for in a black hole binary that has disturbed the center of its host galaxy.
The study reports a relative velocity of about 370 kilometers per second between the two sources. That speed suggests motion inside a shared gravitational system. In plain language, the two black holes appear to be moving around a common center.
The combined mass estimate is extraordinary. The team places the total mass near 60 billion times the mass of the Sun, with uncertainty around that number. A pair that massive would exceed the scale of most known supermassive black hole binaries.
The result remains framed with care. The paper title itself says the cavity may be caused by dynamic interactions with an ultramassive black hole. That wording matters because the system is distant, complex and observed through indirect signatures.
How black holes can clear a galactic core
Galaxy mergers provide the likely setup. When two massive galaxies collide, their central black holes gradually sink toward the merged galaxy’s center. The black holes lose energy through interactions with stars and gas, then settle into an orbit around each other.
As a binary black hole tightens, its gravity can act like a slingshot. Stars that pass too close can gain speed and get kicked into wider orbits. Over time, this process can hollow out a central region and leave behind a stellar cavity.
In Abell 402-BCG, that mechanism could explain the missing stars. The cavity’s size and location match the idea of a powerful central pair repeatedly scattering stars away from the middle of the galaxy. The result would be a smooth-looking void carved by gravity over millions of years.
The study also discusses a broader core structure about 6,500 light-years across. That larger feature may record an earlier stage in the galaxy’s merger history. A previous black hole interaction could have shaped the wider core before the current pair became visible.
This layered history is common in the largest galaxies. They grow through many encounters and each merger can leave traces in the distribution of stars. In this case, the trace may be unusually clear because the central cavity is large and sharply defined.
A rare stage before the final merger
Only a small fraction of massive galaxies should be caught during this stage. The black holes spend a limited amount of cosmic time in a close binary configuration that is both active and observable. That makes Abell 402-BCG a valuable target for studying how the largest black holes grow.
The current pair may have orbited together for only a few tens of millions of years. That is a brief interval compared with the age of a giant elliptical galaxy. For astronomers, it offers a snapshot of a process that usually unfolds across immense stretches of time.
Eventually, the two black holes may merge into one even larger object. Such a merger would release energy through gravitational waves, ripples in spacetime produced by accelerating massive bodies. Present-day gravitational-wave detectors are tuned mainly to smaller black hole mergers, while future observatories may probe heavier systems across cosmic distances.
The finding also gives researchers a practical search strategy. Other galaxies with strange central cavities could be examined with JWST observations, optical data and spectroscopy to look for similar paired active nuclei. A dark center can become a clue to the hidden history of a galaxy.
For now, Abell 402-BCG stands out as a striking case of cosmic excavation. Its hollowed-out heart may preserve the gravitational fingerprints of two black holes so massive that their dance reshaped the core of an entire galaxy.
