Three supermassive black holes found in a distant galaxy—and they may collide

Astronomers have discovered three active supermassive black holes in a single galaxy. The galaxy is so distant that we see it as it was less than 1.3 billion years after the Big Bang. The finding provides fresh evidence that black holes in the early Universe grew rapidly, in part through mergers, reports Space.com.

What was observed

The galaxy J0148‑4214 is so far away that the James Webb Space Telescope could not directly resolve the black holes themselves. Instead, the NIRSpec spectrograph measured the motion of hydrogen in the accretion disks around each of them.

Lead researcher Hannah Übler from the Max Planck Institute for Extraterrestrial Physics noted that this was the first evidence of three active black holes in a single galaxy in the distant Universe, adding that it shows how effectively massive black holes were brought together in the early Universe, setting the stage for the mergers that future gravitational‑wave observatories are expected to detect.

The galaxy's stellar mass is about 1.3 billion solar masses, and the black holes make up a notable fraction of it.

How the triple system is arranged

Two of the black holes lie at the galaxy's centre, separated by about 620 light‑years. One is very massive—around 80 million solar masses. The second is significantly smaller, at about 600,000 solar masses, but it is growing extremely rapidly, exceeding the Eddington limit. Such a "overfeeding" mode cannot last long: the radiation from the accretion disk will eventually begin to push material away.

The third black hole is located about 5,500 light‑years from the centre and has a mass of around two million solar masses—roughly half the mass of Sagittarius A* at the centre of the Milky Way. It is thought that this black hole, and possibly the smaller of the central pair, entered the galaxy through mergers with other galaxies.

Roberto Maiolino from the University of Cambridge emphasised that these results are extremely interesting, suggesting that black hole mergers could have been an additional rapid growth pathway in the early Universe.

Will they collide?

It is not certain that all three will eventually merge. In three‑body systems, complex interactions are possible. The more massive black hole could have "captured" the smaller one from the pair and ejected the third at high speed—much as Sagittarius A* sometimes ejects hypervelocity stars from the Milky Way.

There is as yet no data on the direction of the third black hole's motion, so it is unclear whether a merger awaits it or whether it is already leaving the galaxy. If it has been ejected, it may still be travelling through intergalactic space, 12.5 billion years later.

Why this matters for the future

Mergers of supermassive black holes produce long‑wavelength gravitational waves that ground‑based detectors such as LIGO cannot currently capture. To detect them, the European Space Agency is preparing the LISA space observatory—three spacecraft in a triangular formation with arms about 2.5 million kilometres long. Its launch is planned for the mid‑2030s.

The study was published in the journal Astronomy & Astrophysics.

In brief

Three active supermassive black holes have been detected in a galaxy that existed less than 1.3 billion years after the Big Bang. This is the first such evidence in the distant Universe. The finding supports the idea that mergers helped black holes grow rapidly. However, the third black hole may not collide with the others but instead be ejected from the system. The work was published in the journal Astronomy & Astrophysics.