Updated | The very first supermassive black holes appear to have been formed by supersonic gas left over from the Big Bang, scientists have said. The discovery potentially solves one of the biggest mysteries of the universe—how these objects existed when the universe was just one billion years old.
We do not really know how supermassive black holes form, but several theories have been put forward to explain their existence. One suggests they form from the collapse of massive stars. Another theory supposes that these phenomena start as normal-sized black holes, but grow over the years by consuming enormous quantities of matter. A third idea relates to the formation of galaxies and the huge clouds of gas that accumulate during this process. When these clouds eventually collapse, supermassive black holes are born.
But none of these theories satisfactorily explain the very first supermassive black holes, because their formation would have taken far, far longer than one billion years.
In a study published in Science, an international team of researchers created a scenario in which supermassive black holes could form within the given timeframe after the Big Bang. The team, led by Shingo Hirano, from the University of Texas, conducted a series of supercomputer simulations until they found a model that could account for the fast-forming supermassive black holes.
In this model, gas ejected after the Big Bang was traveling at supersonic speeds, which prevented it from forming into a cloud until it had accumulated a huge amount of material. When this accumulation did eventually happen, it formed a giant protostar—a contracting mass of gas that marks an early stage of star formation.
This giant protostar grew quickly, reaching an estimated 34,000 solar masses before it collapsed catastrophically, leaving behind “a promising seed for the formation of a monstrous black hole,” the scientists wrote.
"Once reaching the mass of 34,000 times that of our sun, the star collapsed by its own gravity, leaving a massive black hole. These massive black holes born in the early universe continued to grow and merge together to become a supermassive black hole,” principal Investigator Naoki Yoshida, from the University of Tokyo, said in a statement.
"This is significant progress. The origin of the monstrous black holes has been a long-standing mystery and now we have a solution to it.”
Commenting on the study, Andrew Fabian, Director of the Institute of Astronomy at the University of Cambridge, U.K., tells Newsweek: "The work is interesting and at the current state of the art in galaxy simulation. They appear to have a plausible solution to the long standing puzzle as to high billion solar mass black holes are found within 3 Gyr [three billion years] of the Big Bang. However it does require that the material is pristine and metal free, so no stars have formed to pollute the gas.
"This can perhaps apply to a few extreme objects but not to more typical ones which have to form from much lower mass stars."
Other astrophysicists have different ideas on how the first supermassive black holes formed. In March, another team of researchers said such formations could emerge if they are able to feast on neighboring galaxies. Published in Nature Astronomy, the team found that if a nearby galaxy emitted enough radiation, its star-making abilities would be shut down. If this event happened, nearby black holes could feed on the galaxy and become enormous.
Future observations using the James Webb Telescope, which is scheduled to launch next year, should help astrophysicists better understand primordial supermassive black holes and how they formed.
This article has been updated to include quotes from Andrew Fabian.