You’ve likely been there–snoozing on the couch after a large or decadent meal. A similar phenomenon is being observed with a black hole detected in the early universe. Using the NASA/ESA/CSA James Webb Space Telescope (JWST) a team of scientists detected a black hole that is laying dormant after consuming too much matter. The sleepy black hole is described in a study published December 18 in the journal Nature.
Eat, sleep, repeat
The black hole is located in the early universe, existing just 800 million years after the big bang. It is also massive. At 400 million times the mass of our sun, it is one of the largest black holes that JWST has observed at this point in the universe’s development. It is so large that it makes up about 40 percent of the total mass of its host galaxy. By comparison, most black holes in the local galaxy are only about 0.1 percent of their host galaxy mass.
Despite this enormous size, the black hole is actually accreting–or eating–gas at a very low rate. According to the team, it is only accreting about 100 times below its theoretical maximum limit. It is essentially dormant. That such an enormous black hole located so early in our universe–yet not growing and gobbling up mass–challenges existing models of how these cosmic phenomena develop.
Typically, black holes are detected by a tell-tale glow of a swirling accretion disc. This disc forms near the black hole’s edges and the gas in the accretion disc becomes extremely hot. When it gets hot enough, it begins to glow and radiate energy in the ultraviolet range.
The team believes that the most likely scenario at play here is that black holes go through short bursts of ultra-fast growth and then long periods of dormancy. When black holes are “napping,” like this one, they are much less luminous. This lack of light makes them harder to spot, even with highly-sensitive space telescopes such as JWST. However, this one was big enough.
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“Even though this black hole is dormant, its enormous size made it possible for us to detect,” Ignas Juodžbalis, a study co-author and University of Cambridge astrophysicist, said in a statement. “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.”
A limit exists…
According to our current astronomical models, black holes form from the collapsed remnants of dead stars. They then accrete matter up to a predicted limit astronomers call the Eddington limit. At this point, the pressure of radiation and matter overcomes the gravitational pull of the black hole.
In this case, the sheer size of the dormant black hole suggests that our standard models may not fully explain how holes of this magnitude form and grow.
“It’s possible that black holes are ‘born big’, which could explain why Webb has spotted huge black holes in the early universe,” study co-author and Cambridge astrophysicist Roberto Maiolino said in a statement. “But another possibility is they go through periods of hyperactivity, followed by long periods of dormancy.”
…or does it?
To take a closer look, the team on this new study conducted a range of computer simulations to model how this dormant black hole may have grown to such a massive size so early in the universe. Their results show that the most likely scenario is that black holes can actually exceed the Eddington limit for short periods. When they hit this threshold, they grow very quickly and then go through a long period of inactivity. The team believes that black holes such as this one likely eat for roughly five to 10 million years and then 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 Maiolino.
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Since these dormant periods are much longer than their mega growth eras, it is more likely that astronomers will detect black holes while they are “sleeping.” However, it is still a challenge to detect dormant black holes due to how little light they are giving. The team says that this example is likely part of a larger trend, if the black holes in the early universe are spending the majority of their time in this dormant state.
“It’s likely that the vast majority of black holes out there are in this dormant state,” said Maiolino. “I’m surprised we found this one, but I’m excited to think that there are so many more we could find.”
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