Dark Matter May Not be so Dark: Testing Primordial Black Hole Dark Matter with Galactic X-Ray Emission

Despite its vast importance in the structure of our universe, the origin of dark matter is still unknown. While most candidates include subatomic particles such as axions and WIMPs, others have proposed dark stars, cosmic strings, or primordial black holes (PBHs). Though still a theoretical uncertainty, certain classes of inflation may spawn PBHs over a wide range of masses from grams to 1000s of solar masses, and the most massive among this spectrum could persist as the origin of dark matter. In this framework, PBH dark matter may be tied to the origin of supermassive and intermediate mass black hole seeds, drive early galaxy evolution, produce LIGO's detected gravitational wave signals, as well as provide sources for x-ray binaries (XRBs) and ultraluminous x-ray sources (ULXs) in galaxies. We present preliminary results of treating dark matter as PBHs using the Romulus25 simulation. In particular, we evaluate the electromagnetic signature produced by PBHs as they accrete nearby gas at the present epoch, comparing the results to observed XRBs and ULXs from local galaxies. Romulus25 is a hydrodynamic cosmological zoom in N-body simulation of a 25 Mpc³ volume of the universe with finely-resolved dark matter and gas particles for more accurate black hole dynamics. In our study, we treat the dark matter particles as clusters of PBHs with an initial mass function and sum their luminosities according to the gas they accrete. To simulate the accretion of local gas particles by the PBH dark matter, we use Bondi-Hoyle accretion. Using the Eddington Luminosity, we derive the bolometric luminosities of the PBH dark matter. Comparing our results to recent observations from the Chandra X-ray telescope allows us to constrain the abundance of PBH dark matter in specific mass regimes. Which may have ramifications for the epoch of reionization, the diffuse x-ray background, and the gravitational wave background as seen by LISA.