Black Hole-Black Hole Total Merger Mass and the Origin of LIGO/Virgo Sources

The LIGO-Virgo-KAGRA (LVK) Collaboration has reported nearly 100 black hole (BH)-BH mergers. LVK provides estimates of rates, masses, effective spins, and redshifts for these mergers. Yet the formation channel(s) of the mergers remains uncertain. One way to search for a formation site is to contrast the properties of detected BH-BH mergers with different models of BH-BH merger formation. Our study is designed to investigate the usefulness of the total BH-BH merger mass and its evolution with redshift in establishing the origin of gravitational-wave sources. We find that the average intrinsic BH-BH total merger mass shows exceptionally different behaviors for the models that we adopt for our analysis. In the local universe (z = 0), the average merger mass changes from M ¯ tot , int ∼ 25 M ⊙ for the common envelope binary evolution and open cluster formation channels, to M ¯ tot , int ∼ 30 M ⊙ for the stable Roche lobe overflow binary channel, to M ¯ tot , int ∼ 45 M ⊙ for the globular cluster channel. These differences are even more pronounced at larger redshifts. However, these differences are diminished when considering the LVK O3 detector sensitivity. A comparison with the LVK O3 data shows that none of our adopted models can match the data, despite the large errors on BH-BH masses and redshifts. We emphasize that our conclusions are derived from a small set of six models that are subject to numerous known uncertainties. We also note that BH-BH mergers may originate from a mix of several channels, and that other (than those adopted here) BH-BH formation channels may exist.