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Stellar-mass black holes, which are formed by stars going supernova, weigh between a few and a few dozen times the mass of the Sun. At the center of galaxies, however, there are supermassive black holes weighing millions, if not billions, of times the mass of our Sun. For a long time, astronomers believed that these supermassive black hole grew slowly but in recent years, observations have shown that these giants were already in place and massive long before the first stars formed.
Researchers trying to wrap their heads around these objects' formations have considered quite a few scenarios. Now a paper published in The Astrophysical Journal Letters combines some of those ideas, suggesting that these primordial black holes may have collapsed from a very large cloud of gas that, given the gravity and short time-scale, had no time to break apart and turn into stars. These are called direct-collapse black holes.
These black holes started their lives being massive, but not supermassive, somewhere in the tens of thousands and hundreds of thousands of times the mass of the Sun. These objects are born hungry and surrounded by gas and dust, their favorite meal. They start gobbling up this material at an exceptional rate, quickly growing to massive proportions.
“Supermassive black holes only had a short time period where they were able to grow fast and then at some point, because of all the radiation in the universe created by other black holes and stars, their production came to a halt,” lead author Dr Shantanu Basu, from Western University, said in a statement. “That’s the direct-collapse scenario.”
The new study provides some indirect observational evidence that this scenario is indeed correct. The team constructed a mathematical power-law to estimate how many of these direct-collapse black holes of a certain mass would form. The researchers were able to show that if the black holes continue to grow at a regular pace after their early years, then their luminosity should be consistent with observations seen in the quasars populations.
Quasars are extremely active galaxies whose supermassive black hole accretion processes are outshining all the other stars. Their discovery so early in the history of the universe has been a spanner in the works of massive black hole formation theories. Some of these are already the mass of billions of Suns just 800 million years after the Big Bang. The direct-collapse theory can explain how these objects came to be.
