Constraints on primordial black hole dark matter from Galactic center X-ray observations

TL;DR

This study uses NuSTAR X-ray data and advanced modeling to place constraints on primordial black holes as dark matter candidates, showing that current observations do not exclude black holes of around 10 solar masses.

Contribution

It introduces a comprehensive Monte Carlo analysis with gas turbulence effects and multiple dark matter density profiles to refine constraints on PBH dark matter.

Findings

Gas turbulence significantly reduces PBH accretion rates.

Current X-ray observations cannot exclude 10 solar mass PBHs as dark matter.

Inclusion of profile uncertainties weakens previous constraints.

Abstract

Surprisingly high masses of the black holes inferred from the LIGO & Virgo gravitational wave measurements have lead to speculations that the observed mergers might be due to ${\cal O}(10) M_\odot$ primordial black holes (PBHs). Furthermore, it has been suggested that the whole amount of dark matter (DM) might be in that exotic form. We investigate constraints on the PBH DM using NuSTAR Galactic center (GC) X-ray data. We used a robust Monte Carlo approach in conjunction with a radiatively inefficient PBH accretion model with commonly accepted model parameters. Compared to previous studies we allowed for multiple forms of DM density profiles. Most importantly, our study includes treatment of the gas turbulence, which significantly modifies the relative velocity between PBHs and gas. We show that inclusion of the effects of gas turbulence and the uncertainties related to the DM density profile reduces significantly the gas accretion onto PBHs compared to the claimed values in previous papers. It is highly improbable to obtain accreting PBHs brighter than the NuSTAR point source limit using observationally determined gas velocities. As such, one can safely conclude that GC X-ray observations cannot rule out ${\cal O}(10) M_\odot$ PBH DM.