# New X-ray bound on density of primordial black holes

## TL;DR

This paper establishes new upper limits on primordial black hole abundance using X-ray data, constraining their density across a broad mass range and assessing their potential role in explaining LIGO black hole detections.

## Contribution

It provides the first X-ray based upper bounds on primordial black hole density over a wide mass spectrum, refining previous constraints.

## Key findings

- PBH density constrained across mass range from a few solar masses to 2×10^7 solar masses.
- X-ray data limits PBH contribution to observed compact objects in galaxies.
- PBH density compatible with LIGO black hole origins is marginally allowed.

## Abstract

We set a new upper limit on the abundance of primordial black holes (PBH) based on existing X-ray data. PBH interactions with interstellar medium should result in significant fluxes of X-ray photons, which would contribute to the observed number density of compact X-ray objects in galaxies. The data constrain PBH number density in the mass range from a few $M_\odot$ to $2\times 10^7 M_\odot$. PBH density needed to account for the origin of black holes detected by LIGO is marginally allowed.