What's in a binary black hole's mass parameter?

Vaibhav Tiwari

Published 2023-04-07Version 1

The gravitational wave observations have revealed four emerging peaks in the binary black hole mass distribution suggesting an overproduction of binaries clustered around specific mass values. Although the presence of the first and the third peaks has been attributed to binary black hole formation in star clusters or due to the evolution of stellar binaries in isolation, the second peak, because it lacks significance in the primary mass distribution, has received relatively less attention. In this article, we report that confidence in the second peak depends on the mass parameter we choose to model the population on. Unlike primary mass, when modelled on the chirp mass this peak is significant. We discuss the disparity as a consequence of mass asymmetry in the observations that cluster at the second peak. Finally, we report this asymmetry to be part of a potential trend in the mass ratio distribution which is manifested as a function of the chirp mass, but not as a function of primary mass, when we include the observation GW190814 in our modelling. Chirp mass is not a parameter of astrophysical relevance. Features present in the chirp mass, but not in the primary mass, are relatively difficult to explain and expected to garner significant interest.