A massive black hole sleeping in the early universe challenges existing models

Scientists have spotted a massive black hole in the early universe that is “taking a nap” after stuffing itself with too much food. Like a bear gorging on salmon before hibernating for the winter, or like a well-deserved nap after Christmas dinner, this black hole has overeaten to the point of sleeping in its host galaxy.

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 the Big Bang.

The black hole is enormous – 400 million times the mass of our sun – making it one of the most massive black holes discovered by Webb at this point in the universe’s development. The black hole is so huge that it makes up about 40% of the total mass of its host galaxy: in comparison, most black holes in the local universe make up about 0.1% of the mass of their host galaxy.

However, despite its gigantic size, this black hole consumes or accumulates the gas it needs to grow at a very slow rate – around 100 times lower than its theoretical maximum limit – making it essentially dormant.

A black hole this massive so early in the universe, but not growing, challenges existing models of how black holes grow. However, the researchers say the most likely scenario is that black holes experience short periods of ultra-rapid growth, followed by long periods of dormancy. Their results are reported in the journal Nature.

When black holes “nap,” they are much dimmer, making them harder to spot, even with highly sensitive telescopes such as Webb. Black holes cannot be observed directly, but they are detected by the telltale glow of a swirling accretion disk, which forms near the edges of the black hole. The gas in the accretion disk becomes extremely hot and begins to glow and radiate energy in the ultraviolet range.

“Even though this black hole is dormant, its enormous size allowed us to detect it,” said lead author Ignas Juodžbalis of the Kavli Institute for Cosmology in Cambridge. “Its dormant state also allowed us to learn more about the mass of the host galaxy. The early universe managed to produce absolute monsters, even in relatively small galaxies.”

According to standard models, black holes form from the collapsed remains of dead stars and accumulate matter up to a predicted limit, known as the Eddington limit, where the pressure of radiation on the matter exceeds the gravitational pull of the black hole. However, the sheer size of this black hole suggests that standard models may not adequately explain how these monsters form and grow.

“It is possible that black holes are born large, which could explain why Webb spotted huge black holes in the early universe,” said co-author Professor Roberto Maiolino, of the Kavli Institute and the Cavendish Laboratory, 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 conducted 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 can exceed the Eddington limit for short periods, during which they grow very quickly, followed by long periods of inactivity: the researchers say that black holes like this probably eat for 5-10 hours. million years and lie dormant for about 100 million years.

“It seems counterintuitive to explain a sleeping black hole by periods of hyperactivity, but these short bursts allow it to grow quickly while spending most of its time napping,” Maiolino said.

Because periods of dormancy are much longer than periods of ultra-rapid growth, it is during these periods that astronomers are most likely to detect black holes. “It was the first result I got in my doctorate, and it took me a little while to realize how remarkable it was,” Juodžbalis said. “It was only when I started talking with my colleagues about the theoretical side of astronomy that I was able to understand the true meaning of this black hole.”

Because of their low luminosity, dormant black holes are harder for astronomers to detect, but researchers say this black hole is almost certainly the tip of a much larger iceberg, if black holes in the early universe spend most of their time in a dormant environment. State.

“It’s likely that the vast majority of black holes are in this dormant state. I’m surprised we found this one, but I’m excited to think there are so many more we could find,” Maiolino said.