  We discuss the possibilities for primordial black holes (PBHs) to grow via
the accretion of dark matter. In agreement with previous works, we find that
accretion during the radiation-dominated era does not lead to a significant
mass increase. However, during matter-domination, PBHs may grow by up to two
orders of magnitude in mass through the acquisition of large dark matter halos.
We discuss the possibility of PBHs being an important component in dark matter
halos of galaxies as well as their potential to explain the ultra-luminous
x-ray sources (ULXs) observed in nearby galactic disks. We point out that
although PBHs are ruled out as the dominant component of dark matter, there is
still a great deal of parameter space open to them playing a role in the
modern-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 dark
matter mass by a redshift of $z \approx 30$. These intermediate mass black
holes may then ``light up'' when passing through molecular clouds, becoming
visible as ULXs at the present day, or they may form the seeds for supermassive
black holes at the centers of galaxies.
