Ancestral Black Holes of Binary Merger GW190521

TL;DR

This paper investigates the ancestral origins of the massive black hole merger GW190521, suggesting it may be the product of multiple previous mergers, and estimates the masses of its ancestral black holes.

Contribution

It provides the first estimates of the masses of the ancestral black holes involved in GW190521, exploring the possibility of multiple merger origins for such heavy black holes.

Findings

The heaviest parental black hole has a mass of approximately 62 solar masses.

78% probability that the black hole is in the 50-120 solar mass gap.

Estimated mass distributions for the grandparent black holes are provided.

Abstract

GW190521 was the most massive black hole merger discovered by LIGO/Virgo so far, with masses in tension with stellar evolution models. A possible explanation of such heavy black holes is that they themselves are the remnants of previous mergers of lighter black holes. Here we estimate the masses of the ancestral black holes of GW190521, assuming it is the end product of previous mergers. We find that the heaviest parental black holes has a mass of $62^{+21}_{-19}$ M$_\odot$ (90% credible level). We find 78% probability that it is in the $50$ M$_\odot-120$ M$_\odot$ mass gap, indicating that it may also be the end product of a previous merger. We therefore also compute the expected mass distributions of the "grandparent" black holes of GW190521, assuming they existed. Ancestral black hole masses could represent an additional puzzle piece in identifying the origin of LIGO/Virgo/KAGRA's heaviest black holes.