You’ve probably experienced it before: napping on the couch after an extensive or decadent meal. A similar phenomenon is observed with a black hole detected in the early universe. Using the NASA/ESA/CSA James Webb Space Telescope (JWST), a team of scientists has discovered a black hole that is inactive after consuming too much matter. The sleepy black hole is described in a study published Dec. 18 in the journal Nature.
Eat, sleep, repeat
The black hole is in the early universe and exists just 800 million years after the Big Bang. It’s also huge. With a mass of 400 million times the mass of our sun, that is true one of the largest black holes observed by JWST 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 means of comparisonmost black holes in the local galaxy make up only about 0.1 percent of the mass of their host galaxy.
Despite this enormous size, the black hole is actually collecting (or eating) gas at a very slow rate. According to the teamit only grows about 100 times below its theoretical maximum limit. It is essentially dormant. The fact that such a huge black hole is so early in our universe – but is not yet growing and absorbing mass –challenges existing models of how these cosmic phenomena develop.
Normally, black holes are detected by the telltale glow of a swirling accretion disk. This disk forms near the edges of the black hole and the gas in the accretion disk becomes extremely hot. When it gets warm 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 experience short bursts of ultra-fast growth and then long periods of dormancy. When black holes, like this one, ‘doze’, they are much less luminous. This lack of light makes them more difficult to spot, even with highly sensitive space telescopes such as JWST. However, this one was big enough.
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“Although this black hole is inactive, its enormous size made it possible for us to detect it,” said Ignas Juodžbalis, co-author of the study and astrophysicist from the University of Cambridge. said in a statement. “The dormant state also allowed us to learn more about the mass of the host galaxy. The early universe managed to produce some absolute monsters, even in relatively small galaxies.”
There is a limit…
According to our current astronomical models, black holes form from the collapsed remains of dead stars. They then accumulate matter up to a predicted limit called by astronomers Eddington limit. At this point, the pressure of radiation and matter overcomes the black hole’s gravity.
In this case, the enormous size of the dormant black hole suggests that our standard models may not fully explain how holes of this size form and grow.
“It is possible that black holes are ‘born large’, which could explain why Webb discovered huge black holes in the early universe,” study co-author and Cambridge astrophysicist Roberto Maiolino said in a statement. “But another possibility is that they go through periods of hyperactivity followed by long periods of rest.”
…or is it?
To take a closer look at the team, let’s talk about this new study ran a series of computer simulations to model how this dormant black hole could have grown to such an enormous size so early in the universe. Their show results that the most likely scenario is that black holes can actually exceed the Eddington limit for short periods of time. When they reach this threshold, they grow very quickly and then go through a long period of inactivity. The team thinks black holes like this are likely eat for about five to ten 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 rapidly while snoozing most of the time,” says Maiolino.
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Because these dormancy periods last much longer than their megagrowth epochs, astronomers are more likely to detect black holes while they are “sleeping.” However, it is still a challenge to detect dormant black holes because they emit so little light. The team says this example is likely part of a larger trend, as black holes in the early universe spent most of their time in this dormant state.
“It is likely that the vast majority of black holes are in a dormant state,” says Maiolino. “I’m surprised we found this one, but I’m glad we can find so many more.”
