Astronomers know how stellar-mass black holes form: A massive star collapses under its own gravity. But such a process would seem unable to explain how much larger black holes arise, because they can only gobble material up to a rate known as the Eddington limit, and the universe isn’t old enough for them to have grown from stellar mass to supermassive, said Cole Miller, an astronomer also at the University of Maryland.
“If you feed matter to the black hole too fast, it produces so much radiation that it blows away the matter that’s trying to ,” Miller told Live Science.
How, then, might supermassive black holes form? Some theories suggest these strange behemoths grew from intermediate-mass black holes — which act as “seeds” — that formed in the early stages of the universe from the collapse of giant clouds of gas. Others say these black hole giants started out as stellar-mass black holes that somehow gobbled up material at a rate much faster than the typical limit. Miller has theorized that maybe a dense cluster of stars merged in the early universe, “colliding with each other and sticking together like wet clay,” producing a black hole that gathers mass at a rate exceeding the normal limit. “If you can evade that limit, you might be able to build bigger black holes,” he said.
Priyamvada Natarajan, a theoretical physicist at Yale University in New Haven, Connecticut, and her colleagues recently developed a new theoretical concept that suggests it is possible to grow black holes from a stellar mass seed faster than the Eddington limit, if the seed is trapped in a star cluster feeding off cold, flowing gas. The research was detailed Aug. 7 in the journal Science.
The finding of an intermediate-mass black hole in a nearby galaxy is exciting because it provides a “missing piece” between stellar-mass black holes and supermassive ones, Natarajan told Live Science. “We have very young black holes that are like the infant stage, and we have geriatric ones,” Natarajan told Live Science. Intermediate mass black holes are like the teenagers, she said. Now that Pasham’s team has shown that at least one of these adolescent black holes exists, astronomers will no doubt look for more. Edited from Clue Found to How Black Holes Form