Ellen Phiddian
Cosmos science journalist
Astronomers have found the fastest-growing black hole ever recorded – a colossus that absorbs the equivalent of one Sun every day.
The black hole’s hungry maw makes it the most luminous known object in the universe.
The research is published in Nature Astronomy.
A team of astronomers at the Australian National University (ANU) first spotted an extremely bright quasar with a telescope at Siding Spring Observatory.
“Quasars are bright objects powered by black holes accreting,” Christian Wolf, an associate professor in astronomy at ANU, tells Cosmos.
The researchers used all-sky surveys to focus on parts of the sky that housed bright objects, then tuned ANU’s 2.3-metre telescope to figure out which ones were black holes.
Then, they took their observations to the European Southern Observatory’s Very Large Telescope (VLT) to fully describe the quasars they saw.
Light from the quasar has taken more than 12 billion years to get to Earth, but Wolf says that because of the expansion of the universe, the black hole is now more than 20 billion light-years away.
The black hole is about 17 billion times the mass of our Sun.
“We know of black holes which we estimate to be more massive, in the range from 20-30 [billion Suns],” says Wolf.
“But they would be less hungry black holes. And by accreting less matter, they would also release less heat and light and be less luminous.”
Wolf does not think we will ever find a more luminous object. “I don’t believe the record will be beaten,” he says.
That said, the universe delights in confounding.
Wolf also thought they’d set the record in stone when he and his colleagues reported another extremely bright black hole in 2022. This new black hole is brighter.
“Just a couple of months after that story, we stumbled on to this new object, which is only now getting published [because] all the analysis is finished,” says Wolf.
“But we really found it in 2022, and I felt like ‘oh, God, I have to eat my words, this one is even more exciting’.”
This time around, though, he’s confident they’ve found the brightest. The researchers have now gone over all of their data in detail, which covers 80% of the sky. The remaining portion is obscured by the Milky Way.
“The dust clouds of the Milky Way itself will absorb the light from everything that’s behind, so you only see that foreground. About 20% of the area of the sky is such that with current data and techniques, we can’t search it,” says Wolf.
So, there’s a fairly good chance they’ve found the brightest.
“One should never say never. But I believe we will not find such an outlier again,” says Wolf.
Wolf says that the accretion disc looks like a magnetic storm cell, 7 light-years wide, where temperatures reach more than 10,000°C and lightning flashes “everywhere”.
“In the adolescent universe, matter was moving chaotically and feeding hungry black holes. Today, stars are moving orderly at safe distances and only rarely plunge into black holes,” says study co-author Rachel Webster, a professor of astrophysics at the University of Melbourne.
“It’s a surprise it remained undetected until now, given what we know about many other, less impressive black holes. It was hiding in plain sight,” says study co-author Dr Christopher Onken, a research fellow at ANU.
Wolf says that the discovery would not have been possible without Australia’s 10-year partnership with the European Southern Observatory, so that they could use the VLT.
“The Very Large Telescope is located is arguably the most advanced observatory in the whole world,” he says.
“We would not be able to pull this off by Australia going it alone – we need to be part of these large partnerships.”
