Chirp Mass and Spin of Binary Black Holes from First Star Remnants

TL;DR

This study uses population synthesis simulations to analyze the properties, merger rates, and redshift evolution of Population III binary black holes, highlighting their potential contribution to gravitational wave sources and the importance of future detectors.

Contribution

It provides new insights into the mass, spin, and merger rate evolution of Pop III BBHs, linking stellar evolution in the early universe to observable GW signals.

Findings

Pop III binaries tend to have chirp mass ~30 M_sun.

Merger rate densities at z=0 are consistent with LIGO/Virgo observations.

High spin Pop III BBHs are more common at high redshift.

Abstract

We performed Population III (Pop III) binary evolution by using population synthesis simulations for seven different models. We found that Pop III binaries tend to be binary black holes (BBHs) with chirp mass $M_{\rm chirp} \sim 30~M_{\odot}$ and they can merge at present day due to long merger time. The merger rate densities of Pop III BBHs at $z=0$ ranges 3.34--21.2 $\rm /yr/Gpc^3$ which is consistent with the aLIGO/aVIRGO result of 9.7--101 $\rm /yr/Gpc^3$. These Pop III binaries might contribute to some part of the massive BBH gravitational wave (GW) sources detected by aLIGO/aVIRGO. We also calculated the redshift dependence of Pop III BBH mergers. We found that Pop III low spin BBHs tend to merge at low redshift, while Pop III high spin BBHs do at high redshift, which can be confirmed by future GW detectors such as ET, CE, and DECIGO. These detectors can also check the redshift dependence of BBH merger rate and spin distribution. Our results show that except for one model, the mean effective spin $\left\langle \chi_{\rm eff} \right\rangle$ at $z=0$ ranges $0.02$--$0.3$ while at $z=10$ it does $0.16$--$0.64$. Therefore, massive stellar-mass BBH detection by GWs will be a key for the stellar evolution study in the early universe.