Are binary black hole mergers and long gamma-ray bursts drawn from the same black hole population?

TL;DR

This study compares black hole mergers and long gamma-ray bursts to determine if they originate from the same population, finding they are likely distinct with different formation histories and frequencies.

Contribution

It provides evidence that BBH mergers and LGRBs are separate populations, challenging the idea they share a common origin, and explores their different evolutionary pathways.

Findings

BBH mergers and LGRBs have different formation histories.

LGRBs are more numerous than BBH mergers.

A potential sub-population of fast-spinning LGRB descendants among BBH mergers may dominate at high redshift.

Abstract

This paper compares the population of BBH mergers detected by LIGO/Virgo with selected long GRB world models convolved with a delay function (LGRBs are used as a tracer of stellar mass BH formation). The comparison involves the redshift distribution and the fraction of LGRBs required to produce the local rate of BBH mergers. We find that BBH mergers and LGRBs cannot have the same formation history, unless BBHs mergers have a long coalescence time of several Gyr. This would imply that BHs born during the peak of long GRB formation at redshift z~2-3 merge within the horizon of current GW interferometers. We also show that LGRBs are more numerous than BBH mergers, so that most of them do not end their lives in BBH mergers. We interpret these results as an indication that BBH mergers and LGRBs constitute two distinct populations of stellar mass BHs, with LGRBs being more frequent than BBH mergers. We speculate that the descendants of LGRBs may resemble galactic High-Mass X-Ray Binaries more than BBH mergers. We finally discuss the possible existence of a sub-population of fast-spinning LGRBs descendants among BBH mergers, showing that this population, if it exists, is expected to become dominant beyond redshift z ~ 1, leading to a change in the observed properties of BBH mergers.