The Astro-Primordial Black Hole Merger Rates: a Reappraisal

TL;DR

This paper reevaluates the formation and merger rates of primordial black hole binaries in stellar clusters, proposing a new catalysis mechanism that could explain recent gravitational wave detections like GW190521.

Contribution

It introduces a novel catalysis channel involving exchange interactions for primordial black hole binary formation, addressing previous inefficiencies in merger rate predictions.

Findings

The new catalysis mechanism can produce merger rates consistent with GW190521.

Previous direct capture and three-body mechanisms are less efficient in forming merging binaries.

A higher local overdensity of primordial black holes enhances the likelihood of mergers.

Abstract

Mainly motivated by the recent GW190521 mass gap event which we take as a benchmark point, we critically assess if binaries made of a primordial black hole and a black hole of astrophysical origin may form, merge in stellar clusters and reproduce the LIGO/Virgo detection rate. While two previously studied mechanisms -- the direct capture and the three body induced -- seem to be inefficient, we propose a new "catalysis" channel based on the idea that a subsequent chain of single-binary and binary-binary exchanges may lead to the formation of a high mass binary pairs and show that it may explain the recent GW190521 event if the local overdensity of primordial black holes in the globular cluster is larger than a few.