Formation of Binary Black Holes Similar to GW190521 with a Total Mass of $\sim 150\,M_{\odot}$ from Population III Binary Star Evolution

TL;DR

This paper demonstrates that zero-metallicity Population III binary star evolution can produce binary black holes with total masses around 150 solar masses, matching GW190521, and estimates their merger event rate consistent with observations.

Contribution

It shows that Population III binary star evolution can account for massive binary black holes like GW190521, providing new insights into their formation and merger rates.

Findings

Binary black holes of ~150 M_sun can form from Pop III stars.

Estimated merger rate aligns with LIGO/Virgo observations.

Massive binary black holes are consistent with zero-metallicity star evolution.

Abstract

In the case of zero-metal (population III or Pop III) stars, we show that the total mass of binary black holes from binary Pop III star evolution can be $\sim 150 \,M_{\odot}$, which agrees with the mass of the binary black hole GW190521 recently discovered by LIGO/Virgo. The event rate of such binary black hole mergers is estimated as 0.13--0.66$~(\rho_{\rm SFR}/(6\times10^5~M_{\odot}/{\rm Mpc}^3))~Err_{\rm sys}~{\rm yr^{-1}~Gpc^{-3}}$, where $\rho_{\rm SFR}$ and $Err_{\rm sys}$ are the cumulative comoving mass density of Pop III stars depending on star formation rate and the systematic errors depending on uncertainties in the Pop III binary parameters, respectively. The event rate in our fiducial model with $\rho_{\rm SFR}=6\times10^5~M_{\odot}/{\rm Mpc}^3$ and $ Err_{\rm sys}=1$ is 0.13--0.66$~{\rm yr^{-1}~Gpc^{-3}}$, which is consistent with the observed value of 0.02--0.43$~{\rm yr^{-1}~Gpc^{-3}}$.