A massive black hole in the early universe is ‘napping’ after stuffing itself with too much ‘food’, say astronomers.
Like many of us after an indulgent Christmas dinner, it has become dormant after over-eating.
An artist’s impression of a black hole during one of its short periods of rapid growth. Image: Jiarong Gu
The international team of researchers, led by the University of Cambridge, used the James Webb Space Telescope to detect this black hole, from just 800 million years after the Big Bang.
Some 400 million times the mass of our Sun, it is one of the most massive black holes discovered by the telescope at this point in the universe’s development.
It makes up roughly 40 per cent of the total mass of its host galaxy, whereas most black holes in the local universe are roughly 0.1 per cent of their host galaxy mass.
But it is eating – or accreting – the gas it needs to grow at a very low rate – about 100 times below its theoretical maximum limit – meaning it is effectively dormant.
This challenges existing models of how black holes develop, but the researchers say it is likely that black holes go through short periods of ultra-fast growth, followed by long periods of dormancy – a time when they are far less luminous, making them more difficult to spot.
“Even though this black hole is dormant, its enormous size made it possible for us to detect,” said Ignas Juodžbalis from Cambridge’s Kavli Institute for Cosmology, lead author of the study in the journal Nature.
“Its dormant state allowed us to learn about the mass of the host galaxy as well. The early universe managed to produce some absolute monsters, even in relatively tiny galaxies.”
Black holes cannot be directly observed but are detected by the tell-tale glow of a swirling accretion disc forming near its edges.
When black holes are actively growing, the gas in the accretion disc becomes extremely hot, glowing and radiating energy in the ultraviolet range.
Standard models describe black holes forming from the collapsed remnants of dead stars and accreting matter up to a predicted limit known as the Eddington limit. At this point, the pressure of radiation on matter overcomes the gravitational pull of the black hole.
The sheer size of this black hole suggests standard models may not adequately explain the process.
“It’s possible that black holes are ‘born big’, which could explain why Webb has spotted huge black holes in the early universe,” said co-author Prof Roberto Maiolino, from the Kavli Institute and Cambridge’s Cavendish Laboratory. “But another possibility is they go through periods of hyperactivity, followed by long periods of dormancy.”
The Cambridge researchers worked with colleagues from Italy to conduct computer simulations to model how this dormant black hole could have grown to such a massive size so early in the universe.
The most likely scenario is that black holes can exceed the Eddington limit for short periods, during which they grow very rapidly, followed by long periods of inactivity.
This suggests black holes like this one likely eat for five to 10 million years – and sleep for about 100 million years.
“It sounds counterintuitive to explain a dormant black hole with periods of hyperactivity, but these short bursts allow it to grow quickly while spending most of its time napping,” said Prof Maiolino. “It’s likely that the vast majority of black holes out there are in this dormant state – I’m surprised we found this one, but I’m excited to think that there are so many more we could find.”