Some of the earliest black holes in the universe are bigger than our current theories can explain, but gas left over from the big bang could be the solution
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Mighty winds may explain how black holes can get so big.
Black holes take a long time to grow, so we do not expect to see many huge ones at great distances corresponding to the early universe, from which light is only now reaching us. The smaller black hole “seeds” that grow into these colossal black holes have to reach masses of 10 billion times that of the sun within a billion years after the big bang.
But astronomers keep finding more supermassive black holes there, making it unlikely that they all grew the same way most modern black holes do, by slowly devouring dust and gas.
Shingo Hirano at the University of Texas at Austin and his colleagues used a simulation of conditions in the early universe to figure out how the progenitors of supermassive black holes are born.
Hirano’s black hole seeds started out in a halo of dark matter blasted with supersonic streams of gas left over from the chaos of the big bang. The dark matter’s gravity captured some of the streaming gas, building up a dense cloud.
Normally, a dense cloud of gas would fragment apart and turn into many smaller stars, but the researchers found that the turbulence introduced by the streaming motion prevented the cloud from fragmenting or collapsing for a while.
Eventually, though, the gas cloud did get big enough to collapse in on itself, rapidly building a star thousands of times more massive than the sun. That star became a black hole 2 billion times the mass of the sun less than 800 million years after the Big Bang – much faster than the slow formation of modern black holes.
“Their massive seed black holes form extremely early on — much earlier than discussed in most other works,” says Zoltan Haiman at Columbia University in New York.
The earlier these seeds form, the harder it will be to observe them directly, since we can only see the early universe by looking extraordinarily far away. The only way to definitively test theories of supermassive black holes in the early universe is to use enormous telescopes to look for them – luckily, the next generation of space telescopes may be able to see deep enough into the distant universe to find black hole seeds.
“The formation of seed black holes is one of the most important outstanding questions in supermassive black hole research,” says Jenny Greene at Princeton University in New Jersey. “It will be very exciting to directly test models like this one with the upcoming James Webb Space Telescope.”
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