Scientists have revealed the secret of the birth of the earliest black holes in space


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It takes a long time to grow a supermassive black hole, even if it eats voraciously. So how supermassive black holes billions of times heavier than the sun formed during the first billion years of the universe’s existence remains a mystery.

But new work by an international team of cosmologists offers an answer: Cold matter streams, shaped by mysterious dark matter, are forcibly feeding black holes born from the death of giant primary stars.

“There is a recipe for a black hole with a mass of 100,000 solar masses at birth, and this is a primordial star with a mass of 100,000 solar masses,” said Daniel Whalen, a cosmologist at the University of Portsmouth. Independent. “In the universe today, the only black holes we have detected were formed as a result of the collapse of massive stars. This means that the minimum mass of a black hole should probably be at least three to four solar masses.”

But the gulf is huge between a 4 solar mass star and a 100,000 solar mass star, a “hypergiant” star that, if centered on the Sun, would extend to the orbit of Pluto. For the past 20 years, Dr. Whalen says, much of the research into the universe’s early quasars — the very bright centers of galaxies powered by supermassive black holes — has focused on the carefully chosen set of conditions that would allow such a massive primary star to form.

But in a new article published in the journal NatureDr. Whalen and colleagues are using supercomputer simulations of cosmic evolution to show that hypergiant primordials do not develop from a set of very special circumstances, but form and collapse into quasar “seeds” in a completely natural way from a set of initial conditions that, although still relatively rare are much less delicate. And it all starts with dark matter.

“If you look at the total content, let’s call it the total mass content of energy in the universe, 3 percent of it is in the form of matter that we understand,” Dr. Whalen said, “matter, consisting of protons, neutrons and electrons, hydrogen. , helium and so on. But “24 percent is in the form of dark matter, and we know it exists because of the movement of galaxies and clusters of galaxies, but we don’t know what it is.”

That is, it seems that dark matter interacts with normal matter only through gravity, and the gravity of dark matter is what created the largest structure in the universe: the cosmic web. According to Dr. Whalen, at the beginning of the universe, vast expanses of dark matter collapsed into long filaments under their own weight and pulled ordinary matter with them, forming a web of filaments and their intersections.

Galaxies and stars eventually formed within the filaments, and especially at the material-rich intersections of the filaments.

“We call them halos, cosmological halos,” Dr. Whalen said of the intersections, “and we think primary stars first formed there.”

It was previously thought that in order to form a primary star large enough to form a supermassive black hole and form a quasar within the first billion years of the existence of the universe, the halo must grow to enormous sizes under special conditions: there are no other stars nearby, the formation of molecular hydrogen to keep the gas cold , and supersonic gas flows that maintain halo turbulence. As long as the halo is cool and turbulent enough, it cannot entangle enough to ignite like a star, prolonging its growth phase until it is finally born at enormous size.

And once a massive star ignites, lives its own life, burns up and collapses into a black hole, it must have access to a lot of gas in order to become supermassive, Dr. Whalen said, “because the black hole grows as it grows. swallows gas.”

But rather than requiring finely tuned conditions for the formation of a massive star and eventually a massive black hole, the simulations by Dr. Whalen and his colleagues suggest that cold gas flowing into a halo of dark matter-defined filaments of the cosmic web could replace the many necessary factors for primary star formation in older models.

“If cold accretion flows are fueling the growth of these halos, they must crash into these halos,” Dr. Whalen said, “slamming so much gas onto them so quickly that turbulence can prevent the gas from collapsing and forming a primary star. ”

When they modeled such a halo powered by cold accretion flows, the researchers saw two massive primary stars, one with a mass of 31,000 suns and the other with 40,000 suns. Seeds of supermassive black holes.

“It was wonderfully simple. A problem that existed for 20 years disappeared overnight,” Dr. Whalen said. Any time you have cold streams pumping gas into a halo in the cosmic web, “you’re going to have so much turbulence that you’ll get supermassive star formation and massive seed formation that produces a massive quasar seed.”

This discovery matches the number of quasars observed so far in the early universe, he added, noting that large halos were rare in that early era, as were quasars.

But the new work is a simulation, and scientists would like to actually observe the formation of a quasar in the early universe in the wild. New instruments such as the James Webb Space Telescope could make this a reality relatively soon.

“Webb will be very powerful if he sees it,” said Dr. Whalen, possibly observing the birth of black holes within one or two million years after the Big Bang.

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