Dark matter is an elusive form of matter that is expected to outweigh regular matter five-to-one. Its existence, yet to be confirmed, is necessary to explain a lot of things in the universe. But we don’t know what it is. There have been many proposals that it might be black holes that formed right after the Big Bang. Some have been proven wrong already, but others have seen a resurgence.
Published in The Astrophysical Journal last month, an intriguing piece of research makes a bold claim: If black holes formed spontaneously during the first instants of the universe and most of them have a mass equivalent to 1.4 times our Sun, then these primordial black holes could explain all of the dark matter we expect to exist in the universe.
But that's not all. The existence of such a large population of black holes provides a perfect starting point for the existence of such huge supermassive black holes, hundreds of millions of times the mass of our Sun, even in the early universe. These primordial black holes might be their seed.
“Primordial black holes, if they do exist, could well be the seeds from which all supermassive black holes form, including the one at the center of the Milky Way,” Yale professor of astronomy and physics, Priyamvada Natarajan, said in a statement.
“What I find personally super exciting about this idea is how it elegantly unifies the two really challenging problems that I work on — that of probing the nature of dark matter and the formation and growth of black holes — and resolves them in one fell swoop,” she added.
Primordial black holes can also explain why there might be an excess of infrared radiation in the universe which is synced with X-ray radiation from distant sources. The merging of these primordial black holes could explain that.
“Our study shows that without introducing new particles or new physics, we can solve mysteries of modern cosmology from the nature of dark matter itself to the origin of supermassive black holes,” first author assistant professor Nico Cappelluti, from the University of Miami, explained.
One of the most exciting things about this hypothesis is that it could soon be tested. The brand new JWST, which has successfully deployed its secondary mirror just yesterday meaning it is officially a telescope, is expected to look at the first stars and galaxies in the universe. If dark matter is made of primordial black holes, JWST will be able to see more stars and galaxies forming around them.
The next decade will also see the launch of LISA, the gravitational wave observatory in space. It will be so sensitive that if these primordial black holes are merging, LISA will be able to detect them.
“It was irresistible to explore this idea deeply, knowing it had the potential to be validated fairly soon,” Natarajan concluded.