Effects and possibilities of dark matter of the universe being PBHs.
The velocity dispersion of galaxies and the cosmic microwave background infer the dark matter as the majority of matter component in our universe. Recent detections of gravitational waves from black hole mergers by LIGO have renewed scientists’ interests that primordial black holes (PBHs) could be a candidate of dark matter. We usually consider black holes as a final stage of the stellar (ordinary matter) evolution, whereas PBHs could be directly formed in earlier stage of the universe by, e.g.,cosmic inflation and they thus act as dark matter in the followup cosmic evolution.
Dr. Yuexing Li (professor of PSU and visiting fellow of Tsung-Dao Lee institute) and Dr. Yipeng Jing (professor of SJTU and senior fellow of Tsung-Dao Lee institute) and their research team investigated the effects and possibilities of dark matter of the universe being PBHs. They showed that if the mass range of PBH lies in the window of tens of solar masses, there are several unique effects on galactic scales that are different compared to the models of other types of dark matter (e.g. composed by exotic weakly interactive particles), and these effects can be compared with observations.
In particular, PBHs, act as dark matter, and stars, act as observable ordinary matter, interact and exchange energy (aka. two-body relaxation) in dwarf galaxies and can eventually change the density profiles and velocity dispersions of both components. Fortunately these properties of the star component are more prominent and observable.
The team used Fokker-Planck simulations and Markov chain Monte Carlo modelling to study the evolution of galaxy halos containing both stars and PBH dark matter and to compare the result with observations. By a joint constraint from the observed half-light radius and central stellar velocity dispersions of compact ultra-faint dwarf galaxies, they suggested that these PBHs most likely to have masses between 2 and 14 solar masses, if dark matter is completely made of PBHs. Meanwhile, the research team emphasizes that their models are inconclusive and that the nature of dark matter is still elusive.
This report is written by Dr. Haoran Yu, postdoctoral fellow of the Tsung-Dao Lee institute.