Examining the Gap in the Chirp Mass Distribution of Binary Black Holes

The mass distribution of binary black holes inferred from gravitational wave measurements is expected to shed light on their formation scenarios. An emerging structure in the mass distribution indicates the presence of multiple peaks around chirp masses of $8M_\odot$, $14M_\odot$, and $27M_\odot$. In particular, there is a lack of observations between chirp masses of 10 and 12 $M_\odot$. In this letter, we report that observations significantly favour the model supporting suppression of the rate in a narrow chirp mass range compared to the model that doesn't include suppression at a confidence greater than 99.5\%. Using another test, which measures the deviation between the inferred chirp mass distributions from the two models, we conservatively estimate a 95\% confidence in the presence of a feature. A lack of confidence has been reported in the presence of a gap around a comparable location in the component mass distribution. The differing conclusions are due to a unique correlation between the primary~(heavier of the two masses) and the secondary~(lighter of the two masses) masses of binary black holes. This correlation results in increased clustering of measured chirp masses around specific values.