Scientists discover the secret of the birth of the first black holes in the cosmos

It takes a long time to develop a supermassive black hole, even if it eats voraciously. So how supermassive black holes billions of times heavier than the Sun formed during the universe’s first billion years has been a lingering puzzle.

But new work from an international team of cosmologists suggests an answer: streams of cold matter, shaped by mysterious dark matter, force-feeding black holes born from the death of gigantic primordial stars.

“There is a recipe for creating a 100,000 solar mass black hole at birth, and that is a 100,000 solar mass primordial star,” said Daniel Whalen, a cosmologist at the University of Portsmouth. The Independent. “In the universe today, the only black holes we have discovered, all formed from the collapse of massive stars. So this means that the minimum mass of a black hole must probably be at least three to four solar masses.

But the chasm is immense between a star of 4 solar masses and a star of 100,000 solar masses, a “hypergiant” star which, if it were centered on the Sun, would extend to the orbit of Pluto. Over the past 20 years, Dr Whalen said, much of the research into the universe’s earliest quasars – very bright centers of galaxies powered by supermassive black holes – has focused on all of finely tuned conditions that would allow such a massive primordial star to form.

But in a new article published in the journal Nature, Dr. Whalen and his colleagues use supercomputer modeling of cosmic evolution to show that instead of developing from a very particular set of circumstances, hypergiant primordial stars form and collapse in the “seeds” of quasars quite naturally from a set of initial conditions which, 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 energy content of the mass of the universe, 3% of that is in the form of matter that we understand,” said Dr Whalen – matter made up of protons , neutrons and electrons, hydrogen, helium and so on. But “24% is in the form of dark matter, and we know it’s there because of the movement of galaxies and galaxy clusters, but we don’t know what it is.”

In other words, dark matter only seems to interact with normal matter through gravity, and the gravity of dark matter is what created the largest scale structure in the universe: the cosmic web. In the early universe, vast expanses of dark matter collapsed into long filaments under its own weight, Dr. Whalen said, and dragged normal matter down with it, forming a network of filaments and their intersections.

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

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

Previous thinking held that to form a primordial star large enough to give rise to a supermassive black hole and create a quasar within the first billion years of the universe, a halo would have to grow to massive proportions under specific conditions: no another star too close, the formation of molecular hydrogen to keep the gas cool, and supersonic flows of gas maintaining the turbulent halo. As long as the halo is cold and turbulent enough, it cannot be cohesive enough to ignite as a star, prolonging its growth phase until it is finally born to enormous size.

And once a massive star ignites, lives its life, burns up and collapses into a black hole, it needs access to large amounts of gas to become supermassive, Dr. Whalen said, “because the way the black hole grows is by swallowing gas”.

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

“If cold accretionary flows are fueling the growth of these halos, they must be pounding these halos,” Dr. Whalen said, “pounding them with so much gas so quickly, that the turbulence could prevent the gas from collapsing and to form a primordial star.”

When they simulated such a halo fed by cold accretionary flows, the researchers saw two massive primordial stars forming, one as massive as 31,000 suns and the other as massive as 40,000 suns. The seeds of supermassive black holes.

“It was beautifully simple. The problem for 20 years disappeared overnight,” Dr Whalen said. Whenever 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.”

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

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

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

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