Population of Binary Black Holes Inferred from One Hundred and Fifty Gravitational Wave Signals

TL;DR

This paper analyzes over 150 gravitational wave signals to characterize the population of binary black holes, revealing mass and spin distributions, correlations, and potential hierarchical merger origins.

Contribution

It introduces the Vamana mixture-model framework to infer detailed population properties and identify features suggestive of hierarchical black hole mergers.

Findings

Peak in primary mass near 10 solar masses

Distinct peaks in chirp mass at 14 and 27 solar masses

Correlation between primary and secondary masses

Abstract

The LIGO-Virgo-KAGRA collaborations have reported gravitational wave signals from more than 150 binary black holes in the fourth catalog (GWTC-4). Here, we investigate the population properties of these binary black holes using the mixture-model framework Vamana. We present one-dimensional distributions of masses and spins, explore their correlations, and examine their evolution with redshift. These features may reflect astrophysical processes associated with binary black hole formation channels, although most remain poorly constrained. A notable feature is a peak near $10M_\odot$ in the primary mass and $8M_\odot$ in the chirp mass. Additionally, the primary and secondary masses correlate uniquely, producing pronounced peaks in the chirp mass around $14M_\odot$ and $27M_\odot$. The three peaks are roughly separated by a factor of two. A simple explanation for such well-placed peaks is a hierarchical merger scenario, in which the first peak arises from mergers of black holes of stellar origin, and higher-mass peaks arise from repeated mergers of black holes from lower-mass peaks. Although most binaries do not exhibit the high spins and characteristic mass ratios expected from hierarchical mergers, those that do are associated with the peaks observed in the chirp mass distribution.