Astronomers have long been puzzled by supermassive black holes that seem to have fully formed in the earliest epochs of the universe. Now, a new paper suggests that these monster black holes may have emerged at the dawn of the Big Bang as tiny, primordial "seeds."
Almost all galaxies host supermassive black holes in their cores. They range in size from about 100,000 times the mass of the sun to billions of solar masses. Most surprisingly, observations with the James Webb Space Telescope (JWST) have revealed that these giants existed at the very edge of the cosmic dawn, just a few hundred million years after the Big Bang, right after the first stars and galaxies started forming.
The challenge with supermassive black holes appearing so early is that we know of only one way to form black holes: through the deaths of massive stars. Stars need to form, live, die and leave behind black holes. Then they need to merge and accrete new material to reach monstrous proportions, — all within an incredibly short amount of time.
This unusual situation has spurred researchers to come up with clever ways to quickly build giant black holes. In a paper submitted to the Journal of Cosmology and Astroparticle Physics, researchers propose a radical solution: These giant black holes may have been born in the incredibly early universe.
In the 1970's, Stephen Hawking proposed that the universe may have naturally produced copious numbers of tiny black holes in the first few moments of the Big Bang. These black holes wouldn"t come from the collapse of stars; rather, they would be born directly from matter and energy compressed to high densities in the chaotic fluctuations of those early epochs.
Hawking suggested that these black holes, which could be as small as asteroids, would slowly dissolve through so-called Hawking radiation and be visible in the present-day universe. Decades of surveys have not found any evidence for these primordial black holes, so we know that if they exist, they must make up a tiny fraction of all the matter in the universe.
But that would be more than enough: The researchers found that even a small fraction of primordial black holes could grow over the course of 100 million years. If those black holes found themselves in the densest collections of matter, they could have accreted enough material to reach supermassive status in the epoch in which JWST observed them.
In this scenario, giant black holes — quite possibly even the one in the center of the Milky Way — wouldn’t grow after the formation of the first stars and galaxies but rather in parallel with them. They would gain most of their mass during the cosmic dark ages, the time before starlight shone throughout the universe. When those first stars did ignite, they would have shared the cosmos with giant, hulking monsters.
At this stage, the idea is only a hypothesis. The researchers propose that this model of black hole growth should be incorporated into simulations of the development of the first stars and galaxies to see how realistic the scenario is. Then, they can compare those more realistic black holes to observations and see if this explains the mystery.
