GW190521 Mass Gap Event and the Primordial Black Hole Scenario

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.

Mass and Rate of Hierarchical Black Hole Mergers in Young, Globular and Nuclear Star Clusters

“…Hence, hierarchical mergers can build up IMBHs and also partially fill the pair instability mass gap between ∼60 and ∼120 M [103][104][105][106][107][108]. For this reason, hierarchical mergers are one of the most likely formation scenarios for GW190521 [109,110], as already explored by several authors ( [111][112][113][114][115][116], but see [55,56,[117][118][119][120][121][122][123][124][125][126] for other possible scenarios).…”

GW200105 and GW200115 are compatible with a scenario of primordial black hole binary coalescences

“…where m * and σ stand for the center mass and width, respectively [18,20,23]. In this work, we consider two different methods to determine values of m * and σ .…”

“…First, we assume that all observed black hole binaries are primordial. The results have been shown to be m * = 19M and σ = 0.97 [20], which will be used in this work. There are also alternative choices of mass function [18], which would not significantly change our results of the abundance of PBHs.…”

“…In the case of the broad mass distribution, the mass function is determined by all the observed black hole binaries, since all of them are assumed to be primordial. This has been done by using maximum-likelihood analysis in an existing literature [20]. In our work, the merger rate is predicted via integration over m i ∈ [2.5, 40]M and m j ∈ [1, 3]M , following a method consistent with Ref.…”

“…In the following, we will compute the merger rate density of PBHs in two specific models by following Ref. [20]. The first one assumes that the mass function is determined by GW200105 and GW200115.…”