Somewhere about 12.5 billion light-years away sits a galaxy with a problem most galaxies would envy. It has three supermassive black holes, and all three are feeding at the same time. Astronomers led by the Max Planck Institute for Extraterrestrial Physics found the trio packed inside a single young galaxy called J0148-4214, and the light carrying the news left home when the universe was barely 1.2 billion years old. The announcement landed on 12 August, and it is the first time anyone has caught three active black holes sharing one galaxy in the distant cosmos.
The three are wildly mismatched. The heavyweight tips the scales at roughly 80 million suns. A much smaller sibling, around 600,000 solar masses, sits right beside it near the galactic centre and is gorging so hard it breaks the theoretical speed limit for how fast a black hole should be able to eat. The third, about two million suns, drifts out in the galaxy’s suburbs, some 5,500 light-years from the middle. The two central ones are close enough, about 620 light-years apart on the sky, that they are on course to crash into each other.
Finding a black hole you cannot actually see
None of these three shows up as a tidy dot in an image. The galaxy is too far, and the two central black holes sit too close together for any telescope to split them apart by eye. So the team leaned on the James Webb Space Telescope’s NIRSpec instrument and a technique called spectro-astrometry, which measures tiny shifts in where particular colours of light come from across the galaxy.
The giveaway is hydrogen. Gas whipping around a black hole moves fast, and that speed smears its light into a telltale signature. In the crowded centre, the spectrum only made sense if two separate black holes were tugging on the gas. A third fingerprint turned up in the outskirts. Without that spatial detail, lead author Hannah Ubler and colleagues reckon only one of the three would have been noticed at all.
The one that eats too fast
The middle-weight, that 600,000-solar-mass object, is the show-off. It is accreting above the Eddington limit, the rough ceiling astronomers use for how quickly a black hole can pull in matter before its own radiation blows the buffet away. Objects that break that limit are exactly the sort of fast growers theorists need to explain how monster black holes got so big so soon after the Big Bang.
Why three at once is a big deal
Black holes in the early universe grew alarmingly quickly, and nobody is entirely sure how. One favoured answer is mergers. Galaxies bumped into each other, their central black holes sank together, and each collision built something heavier. A galaxy caught mid-pile-up, with a central pair due to merge within a few hundred million years, is a live snapshot of that process. It also offers future gravitational-wave observatories such as LISA a preview of the signals they will be hunting for.
The oddball in the outskirts
The third black hole, sitting well away from the centre, is the intriguing one. It might be the survivor of an earlier merger, kicked out of the middle by the recoil when two black holes joined. Or it could be sliding inward for a future collision of its own. Either way, the whole system, published in Astronomy and Astrophysics as part of the BlackTHUNDER survey, suggests the early cosmos was a rougher, more crowded place than the calm galaxies around us let on.
Did you know: the most distant black hole merger Webb has spotted so far took place when the universe was only about 740 million years old, according to the European Space Agency.
Sources
- Max Planck Society: three black holes in a young galaxy
- Phys.org coverage
- Ubler et al., Astronomy and Astrophysics
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