Physicists at UC Berkeley have dismissed the possibility that the mysterious dark matter of the universe could consist of a fullness of black holes scattered throughout the universe, contrary to speculation after the detection of gravitational waves.
Based on a statistical analysis of 740 of the brightest supernovae discovered since 2014, and the fact that none of them seems to be magnified or illuminated by “gravitational lenses” of hidden black holes, the researchers concluded that primordial black holes cannot compensate more than about 40 percent of the dark matter in the universe.
Essentially, this means that primordial black holes could only have been created within the first milliseconds of the Big Bang as regions of the universe with a mass concentrated tens or hundreds of times greater than that of the sun collapsed into objects a hundred kilometers wide.
The discoveries indicate that none of the dark matter in the universe consists of heavy black holes, or any similar object, including massive compact halo objects, called MACHOs.
Black Matter—A never-ending mystery
Dark matter is one of the most embarrassing enigmas of astronomy: although it comprises 84.5 percent of the matter in the known cosmos, no one can find it. Essentially it is there, but it’s not.
“Proposed dark matter candidates span nearly 90 orders of magnitude in mass, from ultralight particles like axions to MACHOs,” explain experts at UC Berkeley.
Several theorists have proposed different types of scenarios in which there are multiple types of dark matter. However, if dark matter consists of several unrelated components, each would require a different explanation for its origin, and this fact makes the models very complex.
“I can imagine it being two types of black holes, very heavy and very light ones, or black holes and new particles. But in that case one of the components is orders of magnitude heavier than the other, and they need to be produced in comparable abundance,” said lead author Miguel Zumalacárregui, a Marie Curie Global Fellow at the Berkeley Center for Cosmological Physics.
“We would be going from something astrophysical to something that is truly microscopic, perhaps even the lightest thing in the universe, and that would be very difficult to explain,” added Zumalacárregui.
This research was published in Physical Review Letters.