Observational Aspect of Black Hole Dark Matter

TL;DR

This paper explores the potential for high-resolution astronomy to detect or constrain black hole dark matter through angular deviation effects, especially focusing on primordial black holes and their impact on cosmic microwave background observations.

Contribution

It provides a theoretical analysis of how angular deviations caused by black hole dark matter could be observed or constrained with current and future astronomical resolutions.

Findings

Current resolution limits imply black hole masses less than 10^7 solar masses for detection.

Higher resolutions could significantly improve constraints or enable detection of primordial black holes.

Angular deviations increase with black hole density and redshift effects in cosmology.

Abstract

Advances in high angular resolution astronomy make it conceivable that black hole dark matter could be detected via angular deviation effects. Assuming the dark matter in the galaxy is made of solar mass black holes, there is a non-trivial probability that a line-of-sight through the galaxy, leads to micro-arcseconds deviations, a value that has been discussed for various astronomical projects. In cosmology the effects are magnified by an increased density at early times and an opening of angles due to redshift. If the dark matter is made of primordial black holes, present at the CMB, random deflections of the CMB photons lead to a limit on the angular resolution, approximately ${3}\times 10^{-7} \sqrt{M/M_\odot}\, rad$, with $M$ the mass of the black holes. Using the resolutions of $\sim 10^{-3} rad$ demonstrated in observations of the "acoustic peaks" then implies the limit $(M/M_\odot)\lesssim 10^{7}$. While this large value seems uninteresting, improved resolutions would lead to significant limits or conceivably the discovery of primordial black holes.