Growth of Structure Seeded by Primordial Black Holes

We discuss the possibilities for primordial black holes (PBHs) to grow viathe accretion of dark matter. In agreement with previous works, we find thataccretion during the radiation-dominated era does not lead to a significantmass increase. However, during matter-domination, PBHs may grow by up to twoorders of magnitude in mass through the acquisition of large dark matter halos.We discuss the possibility of PBHs being an important component in dark matterhalos of galaxies as well as their potential to explain the ultra-luminousx-ray sources (ULXs) observed in nearby galactic disks. We point out thatalthough PBHs are ruled out as the dominant component of dark matter, there isstill a great deal of parameter space open to them playing a role in themodern-day universe. For example, a primordial halo population of PBHs each at$10^{2.5} M_\odot$ making up 0.1% of the dark matter grow to $10^{4.5} M_\odot$via the accumulation of dark matter halos to account for $\sim 10%$ of the darkmatter mass by a redshift of $z \approx 30$. These intermediate mass blackholes may then ``light up'' when passing through molecular clouds, becomingvisible as ULXs at the present day, or they may form the seeds for supermassiveblack holes at the centers of galaxies.Comment: 10 pages, 5 figures. Submitted to Ap