# Limits on the Mass and Abundance of Primordial Black Holes from Quasar Gravitational Microlensing

## TL;DR

This study uses quasar gravitational microlensing data to constrain the mass and abundance of primordial black holes, finding that intermediate-mass black holes are unlikely to account for dark matter or LIGO gravitational wave sources.

## Contribution

It provides new limits on the mass range and abundance of primordial black holes using extensive microlensing observations, challenging their role as dark matter candidates.

## Key findings

- Negligible fraction of dark matter in black holes outside 0.05-0.45 solar masses
- Approximately 20% of matter in stellar-mass black holes
- Intermediate-mass primordial black holes are inconsistent with microlensing data

## Abstract

The idea that dark matter can be made of intermediate-mass primordial black holes in the $10M_\odot \lesssim M \lesssim 200M_\odot$ range has recently been reconsidered, particularly in the light of the detection of gravitational waves by the LIGO experiment. The existence of even a small fraction of dark matter in black holes should nevertheless result in noticeable quasar gravitational microlensing. Quasar microlensing is sensitive to any type of compact objects in the lens galaxy, to their abundance, and to their mass. We have analyzed optical and X-ray microlensing data from 24 gravitationally lensed quasars to estimate the abundance of compact objects in a very wide range of masses. We conclude that the fraction of mass in black holes or any type of compact objects is negligible outside of the $0.05 M_\odot \lesssim M \lesssim 0.45 M_\odot$ mass range and that it amounts to $20 \pm5$% of the total matter, in agreement with the expected masses and abundances of the stellar component. Consequently, the existence of a significant population of intermediate-mass primordial black holes appears to be inconsistent with current microlensing observations. Therefore, primordial massive black holes are a very unlikely source of the gravitational radiation detected by LIGO.