The GW190521 Mass Gap Event and the Primordial Black Hole Scenario

TL;DR

The paper examines the GW190521 black hole merger event and evaluates its compatibility with primordial black hole scenarios, highlighting the importance of accretion processes before reionization.

Contribution

It demonstrates that GW190521 challenges non-accreting primordial black hole models and suggests accretion before reionization could explain its origin.

Findings

GW190521 cannot be explained by non-accreting PBHs due to abundance constraints.

Accretion before reionization allows PBHs to account for GW190521.

Standard stellar-origin formation is disfavored for the primary black hole.

Abstract

The LIGO/Virgo Collaboration has recently observed GW190521, the first binary black hole merger with at least the primary component mass in the mass gap predicted by the pair-instability supernova theory. This observation disfavors the standard stellar-origin formation scenario for the heavier black hole, motivating alternative hypotheses. We show that GW190521 cannot be explained within the Primordial Black Hole (PBH) scenario if PBHs do not accrete during their cosmological evolution, since this would require an abundance which is already in tension with current constraints. On the other hand, GW190521 may have a primordial origin if PBHs accrete efficiently before the reionization epoch.