Investigating the mixing between two black hole populations in LIGO-Virgo-KAGRA GWTC-3

TL;DR

This study analyzes the mixing between two hypothesized black hole populations in gravitational wave data, finding limited overlap and suggesting the existence of a distinct Gaussian bump black hole population.

Contribution

Introduces a population model to quantify the mixing between power-law and Gaussian bump black hole populations in GWTC-3 data, revealing low overlap and a distinct BGBH population.

Findings

Low mixing level between populations (3.1%)

Minor fraction of Gaussian bump black holes engage in mixing

Identification of a distinct Gaussian bump black hole population

Abstract

We introduce a population model to analyze the mixing between hypothesised power-law and $\sim 35 M_\odot$ Gaussian bump black hole populations in the latest gravitational wave catalog, GWTC-3, estimating their co-location and separation. We find a relatively low level of mixing, $3.1^{+5.0}_{-3.1}\%$, between the power-law and Gaussian populations, compared to the percentage of mergers containing two Gaussian bump black holes, $5.0^{+3.2}_{-1.7}\%$. Our analysis indicates that black holes within the Gaussian bump are generally separate from the power-law population, with only a minor fraction engaging in mixing and contributing to the $\mathcal{M} \sim 14 M_\odot$ peak in the chirp mass. This leads us to identify a distinct population of Binary Gaussian Black Holes (BGBHs) that arise from mergers within the Gaussian bump. We suggest that current theories for the formation of the massive $35 M_\odot$ Gaussian bump population may need to reevaluate the underlying mechanisms that drive the preference for BGBHs.