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

Abstract

Context. Surprisingly high masses of the black holes inferred from the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo gravitational wave measurements have lead to speculations that the observed mergers might be due to 𝒪(10) M⊙ primordial black holes (PBHs). Furthermore, it has been suggested that the whole amount of dark matter (DM) might be in that exotic form. Aims. We investigate constraints on the PBH DM using NuSTAR Galactic center (GC) X-ray data. Methods. 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. Results. 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. Conclusions. One can safely conclude that GC X-ray observations cannot rule out 𝒪(10) M⊙ PBH DM.