Over the past few years, as we’ve looked deeper and farther into the early universe, astronomers have discovered something extremely puzzling.
By the time the universe was a billion years old, giant black holes, billions more massive than our sun, had somehow already formed. Based on what we know about the formation and growth of black holes, the existence of “behemoths” of this size is extremely difficult to explain. How did they appear so soon after the big bang? How did they grow so big?
Recently, supercomputer simulations revealed an origin scenario that explains how they formed without the need for exotic environmental conditions: rare reservoirs of turbulent cold gas that collapsed into stars more massive than any stars in the present Universe.
“In the center of most massive galaxies today, there is a supermassive black hole; They are millions and billions more massive than our Sun. But in 2003, we began to discover quasars like the beacons of the early universe, that is, extremely bright, actively absorbing matter, supermassive black holes that already existed less than a billion years after the Big Bang,” says Daniel Whalen, a cosmologist at the University of Portsmouth in the UK.
According to his own statement, no one knew how they were formed in such an early age. The discovery is particularly exciting because it finally puts an end to a 20-year-old mystery about the origin of the universe’s first supermassive black holes.
There are two main schools of thought regarding the formation of supermassive black holes. The first is the bottom-up model. One massive star dies, leaving behind a black hole about a hundred times more massive than the Sun.
Over time, and a very long time, the black hole swallows matter, growing larger and larger until it accumulates millions and billions more mass than the Sun. Such a thing is very difficult to imagine in quasars of the early universe.
Another option is if everything starts from the “seed” of a fairly large black hole, into which the mass of up to 100,000 Suns is gathered. The stars that must have collapsed to produce these black holes must have very short cosmic lives indeed, about 250,000 years, before collapsing into black holes.
To date, no stars of this mass are known to us, nor are we aware of any current formation mechanisms that would have produced them. However, the simulations showed that in the early universe, when environmental conditions were very different from today, such stars should theoretically have formed at the coalescence of rare but powerful, dense, turbulent streams of cold gas.
According to cosmologists, this would require some truly exotic environmental conditions, such as strong ultraviolet radiation backgrounds or supersonic flows between gas and dark matter. None of these exotic environments resemble the environmental conditions in which these early universe quasars formed.
A team of researchers from the United Arab Emirates University, led by astrophysicist Muhammad Latif, conducted simulations of gas flows, which showed that supermassive black holes were formed spontaneously by the interaction of these flows, without the need for exotic environmental conditions.
In the simulations, the turbulence of the intersecting streams prevented the formation of normal, present-day stars. This usually happens when a clump of matter in a cold cloud collapses under gravity to form a baby star, but when there is too much turbulence, the environmental conditions are not stable enough for this process to occur.
However, in the simulations, the cloud gradually grew so massive that it catastrophically collapsed into two giant stars, 31,000 and 40,000 times the mass of our Sun.
If the gas streams continue to flow into the clouds, billions of massive supermassive black holes could form and grow on the Sun in just a few hundred million years.
“Accordingly, shortly after the cosmic dawn, only primordial clouds should have been able to form massive quasar ‘seeds’, when the first stars formed in the universe.” “These simple, beautiful results not only explain the origin of the first quasars, but also their demography—their numbers in the early universe,” Valen concludes.
According to him, the first supermassive black holes were simply the natural result of structure formation in the cold dark matter cosmology.
The study was published in the journal Nature.
Prepared from port.ac.uk and ScienceAlert.