# Multi-wavelength astronomical searches for primordial black holes

## TL;DR

This paper analyzes radio and X-ray signals from primordial black holes in our galaxy to set new, stronger limits on their contribution to dark matter, improving previous bounds with advanced accretion physics modeling.

## Contribution

It introduces an improved gas accretion model based on numerical simulations and relaxes the monochromatic mass assumption, refining constraints on primordial black hole dark matter.

## Key findings

- Maximum relic density of primordial black holes is about 0.1% of dark matter.
- New upper bounds are two orders of magnitude stronger than previous estimates.
- Future multi-wavelength searches will better probe galactic black hole populations.

## Abstract

If primordial black holes of $\mathcal{O}(1-100) M_{\odot}$ constitute a significant portion of the dark matter in the Universe, they should be very abundant in our Galaxy. We present here a detailed analysis of the radio and X-ray emission that these objects are expected to produce due to the accretion of gas from the interstellar medium. With respect to previous studies, we relax the assumption of a monochromatic mass function, and introduce an improved treatment of the physics of gas accretion onto isolated, moving compact objects, based on a set of state-of-the-art numerical simulations. By comparing our predictions with known radio and X-ray sources in the Galactic center region, we show that the maximum relic density of primordial black holes in the mass range of interest is $\sim 10^{-3}$ smaller than that of dark matter. The new upper bound is two orders of magnitude stronger with respect to previous results, based on a conservative phenomenological treatment of the accretion physics. We also provide a comprehensive critical discussion on the reliability of this bound, and on possible future developments in the field. We argue in particular that future multi-wavelength searches will soon start to probe the galactic population of astrophysical black holes.