Dark matter makes up almost 30% of our universe, yet we still aren’t sure exactly what it is. One suggestion is that dark matter is made up of primordial black holes (PBHs), black holes formed in the very early universe.
Usually, we think of black holes as forming from the deaths of the largest stars — but these PBHs had to be created before stars existed in the universe. A new model from researchers at UCLA shows a way that PBHs could have formed so that they explain all the dark matter observed in the universe.
This model builds on the Standard Model of particle physics, which describes how different particles and forces are related to each other, by adding only one additional term to its equations. In the early universe, particles coalesced together into massive halos, which could possibly collapse to make PBHs. The problem, though, is that in order for these halos to collapse, they’d need to get rid of some of their energy. This updated model describes a way for halos to radiate away that energy, meaning PBHs are, indeed, possible.
The model suggests that if PBHs are small, they could be abundant enough to explain all the mass of dark matter we see. If PBHs are large, they might not be able to explain all of dark matter, but they could still explain a fraction of it and even be detected by LIGO, the Laser Interferometer Gravitational Wave Observatory — meaning we could someday have concrete evidence for them.
Disclaimer: This research is by one of the author's colleagues.