On the mass distribution of the LIGO-Virgo-KAGRA events

The merging black hole binaries detected by the LIGO-Virgo-KAGRA (LVK) gravitational-wave observatories may help us shed light on how such binaries form. In addition, these detections can help us probe the hypothesized primordial black holes, a candidate for the observed abundance of dark matter. In this work, we study the black-hole mass distribution obtained from the LVK binary black hole merger events. In particular, we study the primary mass ${m}_{1}$-distribution of the observed black hole binaries, and also the secondary to primary mass ratio $q={m}_{2}/{m}_{1}$ distribution. We obtain those distributions by first associating a skewed normal distribution to each event detected with a signal to noise ratio $(\mathrm{SNR})>8$ and then summing all such distributions. We also sample black hole binaries from two separate populations of merging binaries to which we associate a redshift from the redshift distribution. One of these is a stellar-origin population that follows a mass-distribution similar to the zero-age mass function of stars. The second population of black holes follows a Gaussian mass-distribution. Such a distribution could approximate a population of black hole binaries formed from earlier black hole mergers in dense stellar environments, or binaries of primordial black holes among other astrophysical processes. For those populations, we evaluate the number of detectable events and fit their combination to the LVK observations. In our work, we assume that stellar-origin binary black holes follow a similar mass-distribution to that of the initial mass-function of stars. We simulate a wide range of stellar-origin black-hole mass distributions. In agreement with the binary black hole merger rates-analysis of the LVK collaboration, we find that studying the observed LVK events can be fitted better by the combination of such a stellar-origin mass distribution and a Gaussian distribution, than by the stellar-origin mass distribution alone. As we demonstrate with some simple examples, our methodology allows for rapid testing of potential theoretical models for the binary black hole mergers to the observed events by LVK.