Two populations of LIGO-Virgo black holes

TL;DR

This paper analyzes LIGO-Virgo data to investigate whether it contains evidence for multiple black hole populations, including astrophysical and primordial origins, and updates constraints on primordial black hole dark matter contribution.

Contribution

It introduces a combined population model and finds primordial black holes alone are disfavoured, suggesting multiple astrophysical populations or a mixture.

Findings

Primordial black holes are strongly disfavoured as the sole population.

The best fit involves a combination of astrophysical and primordial black hole populations.

Primordial black holes in the 2-400 solar mass range make up less than 0.2% of dark matter.

Abstract

We analyse the LIGO-Virgo data, including the recently released GWTC-2 dataset, to test a hypothesis that the data contains more than one population of black holes. We perform a maximum likelihood analysis including a population of astrophysical black holes with a truncated power-law mass function whose merger rate follows from star formation rate, and a population of primordial black holes for which we consider log-normal and critical collapse mass functions. We find that primordial black holes alone are strongly disfavoured by the data, while the best fit is obtained for the template combining astrophysical and primordial merger rates. Alternatively, the data may hint towards two different astrophysical black hole populations. We also update the constraints on primordial black hole abundance from LIGO-Virgo observations finding that in the $2-400M_\odot$ mass range they must comprise less than 0.2% of dark matter.