Scientists find the secret of the birth of the first black holes in the Cosmos

A supermassive black hole takes a long time to grow, even if it eats voraciously. Therefore, knowing how supermassive black holes billions of times heavier than the Sun were formed in the first billion years of the universe has been an ongoing puzzle.

But new work by an international team of cosmologists suggests an answer: flows of cold matter, made up of mysterious dark matter, that feed black holes born from the death of gigantic primordial stars.

“There’s a recipe for creating a 100,000-solar-mass black hole at birth, and it’s a 100,000-solar-mass primordial star,” said Daniel Whalen, a cosmologist at the University of Portsmouth. the independent. “In the current universe, the only black holes we have discovered all formed from the collapse of massive stars. So that means the minimum mass for a black hole probably has to be at least three or four solar masses.”

But the chasm is huge between a star of 4 solar masses and a star of 100,000 solar masses, a “hypergiant” star that, if it were centered on the Sun, would extend to the orbit of Pluto. In the last 20 years, according to Dr. Whalen, much of the research on quasars in the early universe – very bright centers of galaxies powered by supermassive black holes – has focused on the finely tuned set of conditions that would allow the formation of such a massive primordial star.

But in a new article published in the journal NatureDr. Whalen and colleagues use a supercomputer model of cosmic evolution to show that, instead of developing from a very special set of circumstances, primordial hypergiant stars form and collapse into the “seeds” of stars. quasars quite naturally from a set of initial conditions that, while 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 energy content of the total mass of the universe, 3 percent is in the form of matter that we understand,” explained Dr. Whalen – matter made up of protons and neutrons and electrons, hydrogen, helium and else. But “24 percent is in the form of dark matter, and we know it’s there because of the motion of galaxies and galaxy clusters, but we don’t know what it is.”

That is, dark matter only seems to interact with normal matter through gravity, and it is the gravity of dark matter that has created the largest-scale structure in the universe: the cosmic web. According to Dr. Whalen, in the early universe, large tracts of dark matter collapsed into long filaments under their own weight and dragged normal matter with them, forming a network of filaments and their intersections.

Galaxies and stars would eventually form inside the filaments and, in particular, at the matter-rich intersections of the filaments.

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

Previous ideas held that in order to form a primordial star large enough to give birth to a supermassive black hole and create a quasar in the first billion years of the universe, a halo would have to grow to massive proportions under special conditions: that there were no other stars too close, that molecular hydrogen formed to keep the gas cool, and that supersonic flows of gas kept the halo turbulent. As long as the halo is cool and turbulent enough, it won’t be able to cohere enough to ignite as a star, prolonging its growth phase until it’s finally born tremendous in size.

And once a massive star ignites, lives out its life, runs out and collapses into a black hole, it must have access to large amounts of gas to grow supermassive, Dr. Whalen noted, “because the way the black hole black grows is swallowing gas”.

But rather than requiring very tight conditions for the formation of a massive star and eventually a massive black hole, Dr. Whalen and colleagues’ simulation suggests that cold gas flowing into a halo from filaments defined by the dark matter in the cosmic web could replace the multitude of factors needed for primordial star formation in older models.

“If cold accretion flows are fueling the growth of these halos, they must be hitting those halos,” said Dr. Whalen, “hitting them with so much gas so quickly, that turbulence could be preventing the gas from collapsing and forming a star.” primordial”.

When they simulated such a halo fueled by cold accretion flows, the researchers saw two massive primordial stars form, one as massive as 31,000 Suns, and the other as massive as 40,000 Suns. The seeds of supermassive black holes.

“It was wonderfully simple. The 20-year problem disappeared overnight,” Dr. Whalen noted. Whenever there are cold flows pumping gas into a halo in the cosmic web, “there will be so much turbulence that supermassive star formation and massive seed formation will occur that produce a massive quasar seed.”

It’s a finding that matches the number of quasars seen so far in the early universe, he added, noting that large halos at that early time are rare, and so are quasars.

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

“The Webb will be powerful to see one,” Dr. Whalen said, perhaps to see the birth of black holes within a million or two million years of the Big Bang.

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