A team of international astronomers has detected a massive black hole in the early universe that appears to be ‘napping’ or dormant, challenging the existing models of how black holes develop.
The James Webb Space Telescope detected a black hole 400 million times the mass of our sun, making it one of the universe’s most massive black holes discovered by the telescope.
Most black holes make up roughly 0.1% of their host galaxy’s mass, but the black hole at the centre of this study makes up approximately 40% of the total mass of its host galaxy.
“Even though this black hole is dormant, its enormous size made it possible for us to detect,” says Ignas Juodžbalis, lead author of the study from Cambridge’s Kavli Institute for Cosmology.
However, despite its enormous mass, the current rate at which the object is growing or consuming nearby matter is very low, around 100 times below the theoretical maximum.
This theoretical maximum is known as the Eddington limit and refers to the largest amount of radiation pressure needed to overcome the gravitational pull of a black hole.
But the size does not fit in this limit and suggests that current models may not sufficiently explain how these grow and form.
“It’s possible that black holes are ‘born big’, which could explain why Webb has spotted huge black holes in the early universe,” says Professor Roberto Maiolino, a co-author of the study.
“But another possibility is they go through periods of hyperactivity, followed by long periods of dormancy.”
The researchers simulated a variety of models to understand how it could have grown so massive early on in the universe.
They concluded that the most likely scenario is that they can potentially exceed the Eddington limit for short periods, where they grow rapidly, before long inactivity or rest periods.
In the case of this black hole, the researchers say it is likely to consume matter for five to ten million years, and then sleep for about 100 million years.
“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,” says Juodžbalis.
“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,” says Maiolino.
Dormant black holes are more challenging for astronomers to detect because of their low luminosities.
The team suspects there could be many more lurking around the early universe, if they are correct about them spending most of their time in this resting state.
“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,” says Maiolino.
The team’s observations have been published in Nature and were a part of the James Webb Space Telescope Advanced Deep Extragalactic Survey (JADES).
“This was the first result I had as part of my PhD, and it took me a little while to appreciate just how remarkable it was,” says Juodžbalis.
“It wasn’t until I started speaking with my colleagues on the theoretical side of astronomy that I was able to see the true significance of this.”
Black hole theories
