Binary Black Holes population synthesis based on the current LVK observations

The ongoing observations from ground based gravitational-wave observatories have lead to the detection of more than a hundred merger events between black holes. We use the LIGO-Virgo-KAGRA (LVK) observations from 2015 to early 2024, to test the population synthesis of these merging binaries; which will allow us to probe the formation mechanisms and environments of these black holes. We test if the current sample of binary black holes can be explained only by the merger of black holes coming from the collapse of the cores of massive stars, i.e. as just first generation black holes merging with each other. We also test if in addition to the merger between first generation black holes, there is evidence for a second population of black hole binaries in which at least one the binaries’ members is the product of an earlier merger between black holes. These binaries are typically referred to as signals of hierarchical mergers. Such a population can possibly explain the observation of very massive black hole binaries by the LVK collaboration. We also consider that some of the LVK black hole merging binaries are the result of primordial black holes (PBHs), merging inside dark matter halos and in the intergalactic medium. A population of PBHs may also explain the observed increased number of LVK events with black hole masses in the range of ≃ 30 − 40M_⊙. We also discuss how we can possibly disentangle hierarchical merger events from PBH mergers with future data.