Jiarong Gu
Artist’s impression of a black hole during one of its short periods of rapid growth.
Scientists have discovered a huge black hole in the early Universe that is taking a nap after gorging itself on too much food.
Such as a bear that stuffs itself of salmon before hibernating for the winter, or a much-needed nap after Christmas dinner, this black hole ate too much to the point of being Asleep in your galaxy hostess.
An international team of astronomers, led by the University of Cambridge, used the NASA/ESA/CSA James Webb Space Telescope to detect this black hole in the early Universe, just 800 million years after or Big Bang.
Their results were presented in a published in the journal Nature.
The black hole is huge — 400 million times the mass of our Sun — which makes it one of the most massive black holes discovered by Webb at this point in the development of the Universe
The black hole is so big that it represents about 40% of the total mass of the host galaxy: in comparison, most black holes in the local Universe have about 0.1% of the mass of the galaxy that hosts them.
However, despite its gigantic size, this black hole is eatingyour accretarthe gas you need to grow at a very low rate – about 100 times below its theoretical maximum limit – making it essentially dormant.
A black hole so massive so early in the Universe, but not growing, challenges existing modelss of how black holes develop.
However, researchers say the most likely scenario is that black holes will pass through short periods of ultra-fast growthfollowed by long dormant periods.
When black holes are “sleeping”, they are much less luminous, which makes them more difficult to detecteven with highly sensitive telescopes like Webb.
The black holes cannot be observed directlybut are detected by glow of an accretion disk around itwhich forms near the edge of the black hole.
When black holes are actively growing, the gas in the accretion disk becomes extremely hot and begins to glow and radiating energy in the ultraviolet range.
“Although this black hole is dormant, its enormous size made its detection possible,” said lead author Ignas Juojzbalisfrom the Kavli Institute of Cosmology in Cambridge. “Its dormant state also allowed us to learn about the mass of the host galaxy. The early Universe managed to produce some absolute monsters, even in relatively small galaxies.”
According to standard models, black holes form from collapse of dead stars and accumulate matter up to a predicted limit, known as the Eddington limit, at which the radiation pressure on the matter overcomes the gravitational pull of the black hole.
However, the size of this black hole suggests that standard models can not explaining adequately how these monsters form and grow.
“Is it possible that black holes’be born big‘, which could explain why Webb detected huge black holes in the early Universe,” said co-author Professor Roberto Maiolinofrom the Kavli Institute and the Cavendish Laboratory in Cambridge. “But another possibility is that they go through periods of hyperactivity, followed by long periods of dormancy.”
Working with Italian colleagues, the Cambridge researchers carried out a series of computer simulations to model how this dormant black hole could have grown to such a massive size so early in the Universe.
They found that the most likely scenario is that black holes could exceed the Eddington limit for short periods, during which they grow very quickly, followed by long periods of inactivity: researchers say black holes like this probably eat for five to ten million years and sleep for about 100 million years.
“It seems counterintuitive to explain a dormant black hole with periods of hyperactivity, but these short bursts allow it to grow rapidly while spending most of your time sleeping at sixth,” said Maiolino.
Because periods of dormancy are much longer than periods of ultrafast growth, it is during these periods that astronomers are most likely to detect black holes.
“This was the first result I obtained as part of my doctorate and It took me a while to realize how remarkable it was“, said Juodžbalis. “It was only when I started talking to my colleagues on the theoretical side of astronomy that I was able to see the true meaning of this black hole.”
Due to their low luminosities, dormant black holes are more difficult for astronomers to detect, but researchers say this black hole is almost certainly the tip of a much larger icebergif black holes in the early Universe spent most of their time in a dormant state.
“It is likely that the the vast majority of existing black holes is in this dormant state – I’m surprised we found this one, but I’m excited to think that we can find many more“, said Maiolino.
