Mass Ratio of Binary Black Holes Determined from LIGO/Virgo Data Restricted to Small False Alarm Rate

TL;DR

This study analyzes binary black-hole merger data from LIGO/Virgo, revealing distinct mass ratio patterns for different chirp mass ranges, which suggest different astrophysical origins, especially for low and high mass systems.

Contribution

It provides the first detailed statistical analysis of mass ratios in binary black holes with very low false alarm rates, linking observed patterns to possible stellar origins.

Findings

Mass ratio for high chirp mass > 18 M_sun is ~0.723, consistent with population III star origins.

Mass ratio for lower chirp mass < 18 M_sun is ~0.601, indicating a different formation channel.

The probability of these patterns occurring by chance is very low, supporting their astrophysical significance.

Abstract

We focus on gravitational-wave events of binary black-hole mergers up to the third observing run with the minimum false alarm rate smaller than $10^{-5}\,{\rm yr}^{-1}$. These events tell us that the mass ratio of two black holes follows $m_2/m_1=0.723$ with the chance probability of 0.00301% for the chirp mass $M_{\rm chirp} > 18\,M_{\odot}$. We show that the relation of $m_2/m_1=0.723$ is consistent with the binaries originated from population III stars which are the first stars in the universe. On the other hand, it is found for ${\rm chirp} < 18 M_{\odot}$ that the mass ratio follows $m_2/m_1=0.601$ with the chance probability of 0.117% if we ignore GW190412 with $m_2/m_1\sim 0.32$. This suggests a different origin from that for $M_{\rm chirp} > 18 M_{\odot}$.