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One galaxy, three giant black holes — all feeding at the same time, less than a billion and a half years after the universe began. Using the James Webb Space Telescope, an international team led by the Max Planck Institute for Extraterrestrial Physics has found the first evidence of three actively growing supermassive black holes sharing a single galaxy in the distant universe. The galaxy, known as J0148-4214, is so far away that its light has travelled more than 12.5 billion years to reach us: we see it as it was about 1.2 billion years after the Big Bang. The study, published in the journal Astronomy & Astrophysics and highlighted this week by ScienceDaily, lands squarely on one of astronomy's biggest open questions — how black holes grew so enormous, so fast, in the young universe.
Two side by side, one cast out
The three black holes are not equal. Their estimated masses are about 80 million, 2 million and 600,000 times the mass of the Sun. Two of them sit close together near the galaxy's centre, separated by only about 620 light-years — close enough, astronomically speaking, that researchers expect them to spiral together and merge within the next few hundred million years. The third lies much farther out, roughly 5,500 light-years from the centre. And the smallest of the three is, paradoxically, the greediest: the roughly 600,000-solar-mass black hole is pulling in matter faster than its larger neighbour, at a rate that exceeds the Eddington limit — the ceiling that basic models of black hole growth are supposed to impose. As for the lonely third black hole, the team sees two possibilities: it may be the leftover of an earlier merger that was kicked away from the centre by a gravitational recoil, or an object still making its way inwards.
How do you see black holes a telescope cannot separate?
Webb could not resolve the two central black holes as separate points of light — at 12.5 billion light-years, nothing could. Instead, the team used the telescope's NIRSpec instrument in its integral-field spectroscopy mode, studying the light of hydrogen gas moving at high speed around the black holes. Fast gas leaves distinctive fingerprints in a spectrum, and the central signal was too complicated for a single object to explain. Using a technique called spectro-astrometry — tracking tiny shifts in the position of spectral lines across the image — the researchers showed that two nearby black holes best account for what Webb saw, as Nature World News explains in its account of the study. "No previous evidence had established three active black holes sharing one galaxy in the distant universe," said Hannah Übler, the study's lead author and a research group leader at the Max Planck Institute for Extraterrestrial Physics.
The too-big-too-early problem
This is why a trio of black holes in one young galaxy matters far beyond its own system. Ever since Webb began returning data, it has kept finding black holes in the early universe that look too massive for their age — giants that standard growth models, in which black holes fatten slowly by swallowing gas, struggle to explain in the time available. The J0148-4214 finding points to a shortcut: collisions. If young galaxies routinely host more than one growing black hole, mergers can stack mass quickly, and a black hole feeding above the Eddington limit adds a second fast lane. Co-author Roberto Maiolino of the University of Cambridge has pointed to exactly this implication — black hole merging as an additional, fast route for rapid growth in the early universe. It is the observational counterpart to what theorists have been building into models of the cosmic dawn, including the Lumina simulation of the universe's first 2 billion years, in which light from early supermassive black holes drives one of the era's great transformations.
What happens next
The pair at the centre will not merge on any human timescale — "a few hundred million years" is the estimate — but the system gives astronomers something almost as valuable: a snapshot of the process mid-way. If more triple systems turn up in Webb's data, the merger shortcut stops being an exception and becomes part of the standard story of how the first giant black holes were built. If they stay rare, J0148-4214 remains a fascinating oddity. Either way, the early universe is turning out to be a busier, more crowded place than the textbooks described — and this galaxy, with three feeding giants where one would have been remarkable enough, is now the exhibit everyone will cite.