Studying 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 (PBHs), 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. We obtain that distribution by first associating a skewed normal distribution to each event detected with a signal to noise ratio (SNR) $>$ 8 and then summing all such distributions. We also simulate black hole binaries from two separate populations of merging binaries. 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. For those populations, we evaluate the number of detectable events and fit their combination to the LVK observations. In our work, we rely on a wide range of stellar-origin black-hole mass distributions.

We also derive limits for PBHs. We simulate binaries with a merger rate expected for PBHs with different assumptions on the mass distribution of primordial black holes and their merger channels. We then fit the combination of the simulated binary PBHs with the binaries simulated from a power-law distribution to the LVK observations and derive an upper limit of the PBH component to these events.