Over the last few years, as we have been able to look deeper and deeper into the early Universe, astronomers have been discovering something extremely puzzling.
Before the Universe was a billion years old, giant black holes more than a billion times the mass of the Sun had already formed. Given what we know about the formation and growth of the black hole, the presence and size of these giants is extremely difficult to explain. How did they get there, so shortly after the Big Bang? And how did they get so big?
Now, supercomputer simulations have revealed an origin that explains how they formed without the need for exotic conditions: rare deposits of turbulent, cold gas that collapsed into more massive stars than anything in the current Universe. These would have been the big seeds that turned into supermassive black holes.
“We found supermassive black holes in the center of most massive galaxies today, which may be millions or billions of times the mass of the Sun. But in 2003 we began to find quasars: very bright supermassive black holes and of active accretion they are like Cosmic Lighthouses in the early universe, which existed less than a billion years after the Big Bang, ”said cosmologist Daniel Whalen of the University of Portsmouth in the UK.
“No one understood how they formed in such early times. This discovery is especially exciting because it has turned upside down 20 years of thinking about the origin of the first supermassive black holes in the Universe.”
There are two main schools of thought on how supermassive black holes form. The first is the bottom-up model. A single massive star dies, usually leaving behind a black hole about 100 times the mass of the Sun.
Over time, for a long, long time, the black hole absorbs a lot of material, growing and larger until it reaches millions to billions of times the mass of the Sun. This is extremely difficult to reconcile with the quasars of the early Universe.
The other option is if you start with a very large black hole “seed,” up to 100,000 times the mass of the Sun. The stars that collapsed to form these black holes would have had a very, very short cosmic life, perhaps 250,000 years, before collapsing into a black hole.
There are no known stars of this mass around today, and we do not know of any current formation mechanism that can produce them. But simulations have shown that in the early Universe, when conditions were quite different from today, theoretically these stars could have formed at the junctions of rare but powerful currents of dense, turbulent, and cold gases.
Cosmologists thought that some really exotic conditions would be needed, such as strong ultraviolet radiation backgrounds or supersonic fluxes between gas and dark matter. And none of these exotic conditions resembled the environments in which these early quasars of the Universe were found.
Led by astrophysicist Muhammad Latif, of the University of the United Arab Emirates in the United Arab Emirates, the researchers performed simulations of gas streams and were delighted to find that supermassive black holes formed at the intersections of these. currents spontaneously, without the need for exotic conditions. .
In the simulation, the turbulence generated by the intersecting currents prevents normal stars from forming, like the ones we see today. This usually happens when a dense knot of material in a cold cloud collapses under gravity to form a baby star, but when there is too much turbulence, conditions are not stable enough for this to happen.
However, eventually the simulation cloud grew so massive that it catastrophically collapsed into two giant stars, with a mass of 31,000 and 40,000 times that of the Sun.
As the gas from the currents continues to feed in the clouds, a supermassive black hole billions of times the mass of the Sun can form and grow in just a few hundred million years.
“Consequently, the only primordial clouds that could form a quasar just after cosmic dawn, when the first stars in the Universe formed, also conveniently created their own massive seeds. This simple and beautiful result not only it explains the origin of the first quasars but also their demographics: their numbers in the early days, “Whalen concluded.
“The first supermassive black holes were simply a natural consequence of the formation of structures in cold dark matter cosmologies: children of the cosmic network.”
The research has been published in Nature.