Paper detail

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

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.