Primordial Black Holes As Dark Matter

It is too early to say that primordial black holes have been found to comprise the entirety of the dark matter. Here is an accounting of how much of the dark matter can be reasonably expected to be comprised of stellar-mass black holes.

A minimum of 100,000,000,000 MACHOs discovered via microlensing and having a most typical mass of 0.5 solar mass.

Plus a “large” but still unknown number of stellar-mass black holes with masses in the 10–30 solar mass range indicated by the LIGO gravitational wave discoveries.

A newly discovered population of stellar-mass black holes in globular clusters possibly contributing 10,000 to 100,000 BHs per typical galaxy.

The total dark matter content for our Galaxy would require 500,000,000,000 stellar-mass objects and the estimated number of primordial black holes could be reasonably put at on the order of 100,000,000,000 at this point, although these estimates vary from 100,000,000,000 to 500,000,000,000 depending on which papers one cites.

So the dark matter enigma has not been resolved just yet. However, one is certainly justified in noting that a clear trend is emerging. The more places we look, the more places we discover unexpected stellar-mass black holes. Time will tell if these objects (with primordial black holes being the most likely candidates) constitute the entirety of the dark matter.

Robert L. Oldershaw

http://www3.amherst.edu/~rloldershaw

Discrete Scale Relativity/Fractal Cosmology