The Population III origin of GW190521

TL;DR

This paper investigates whether the GW190521 black hole merger originated from Population III stars, using simulations of early star clusters, and finds the dynamical channel best explains the observed event.

Contribution

It introduces improved binary statistics from N-body simulations to evaluate Pop III star cluster merger rates via two evolution channels, favoring the dynamical channel.

Findings

Both evolution channels can explain the observed merger rate.

The dynamical channel aligns better with observations and has fewer parameter restrictions.

Future gravitational wave observations will enhance understanding of Pop III black hole evolution.

Abstract

We explore the possibility that the recently detected black hole binary (BHB) merger event GW190521 originates from the first generation of massive, metal-free, so-called Population III (Pop III), stars. Based on improved binary statistics derived from N-body simulations of Pop III star clusters, we calculate the merger rate densities of Pop III BHBs similar to GW190521, in two evolution channels: classical binary stellar evolution and dynamical hardening in high-redshift nuclear star clusters. Both channels can explain the observed rate density. But the latter is favoured by better agreement with observation and less restrictions on uncertain parameters. Our analysis also indicates that given the distinct features of the two channels (with merger rates peaked at $z\lesssim2$ and $z\sim 10$, respectively), future observation of BHB mergers similar to GW190521 with third-generation gravitational wave detectors will greatly improve our knowledge of the evolution of Pop III BHBs, especially for their dynamics during cosmic structure formation.