GW231123 Formation from Population III Stars: Isolated Binary Evolution

TL;DR

This study explores the origin of the massive black hole merger GW231123 from Population III binary stars, showing it can be explained by specific stellar evolution conditions and constrains models of early star evolution.

Contribution

It demonstrates that GW231123-like events can originate from isolated Pop III binaries under certain stellar evolution assumptions, refining models of early star evolution.

Findings

Pop III binaries can produce GW231123-like events if certain conditions are met.

GW190521 can be formed from Pop III binaries even with standard nuclear reaction rates.

Discovery of GW231123 constrains parameters of single star evolution models.

Abstract

GW231123 is a merger of two black holes (BHs) with estimated masses exceeding $100\;{\rm M}_{\odot}$, making them the most massive BHs discovered to date via gravitational wave (GW) observations. We investigate whether GW231123-like events can originate from isolated Population (Pop) III binary stars using binary population synthesis calculations. Our findings indicate that isolated Pop III binaries can produce GW231123-like events at a rate sufficient to explain the discovery of GW231123, provided that three conditions are met: (i) Pop III stars evolve with inefficient convective overshooting, (ii) the $^{12}\text{C}(\alpha, \gamma)^{16}\text{O}$ rate is $2\sigma$ lower than the standard value, and (iii) Pop III binary stars share the same orbital parameters as Pop I/II binary stars at the initial time. In contrast, GW190521 -- the most massive BH merger in the Gravitational Wave Transient Catalog 3 -- can be formed from isolated Pop III binaries even with the standard $^{12}\text{C}(\alpha, \gamma)^{16}\text{O}$ rate. We demonstrate that the discovery of GW231123 is increasingly constraining the parameter ranges of single star evolution models, under the assumption that these GW events originate from isolated binary evolution.