Rochester Institute of Technology

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The population of merging compact binaries inferred using gravitational waves through GWTC-3
By The LIGO Scientific Collaboration, The Virgo Collaboration, The KAGRA Scientific Collaboration
(Sunday, November 7, 2021)


We report on the population properties of 76 compact binary mergers detected with gravitational waves below a false alarm rate of 1 per year through GWTC-3. The catalog contains three classes of binary mergers: BBH, BNS, and NSBH mergers. We infer the BNS merger rate to be between 13 Gpc−3yr−1 and 1900 Gpc−3yr−1 and the NSBH merger rate to be between 7.4 Gpc−3yr−1 and 320 Gpc−3yr−1 , assuming a constant rate density versus comoving volume and taking the union of 90% credible intervals for methods used in this work. Accounting for the BBH merger rate to evolve with redshift, we find the BBH merger rate to be between 17.3 Gpc−3yr−1 and 45 Gpc−3yr−1 at a fiducial redshift (z=0.2). We obtain a broad neutron star mass distribution extending from 1.2+0.1−0.2M⊙ to 2.0+0.3−0.2M⊙. We can confidently identify a rapid decrease in merger rate versus component mass between neutron star-like masses and black-hole-like masses, but there is no evidence that the merger rate increases again before 10 M⊙. We also find the BBH mass distribution has localized over- and under-densities relative to a power law distribution. While we continue to find the mass distribution of a binary's more massive component strongly decreases as a function of primary mass, we observe no evidence of a strongly suppressed merger rate above ∼60M⊙. The rate of BBH mergers is observed to increase with redshift at a rate proportional to (1+z)κ with κ=2.7+1.8−1.9 for z≲1. Observed black hole spins are small, with half of spin magnitudes below χi≃0.26. We observe evidence of negative aligned spins in the population, and an increase in spin magnitude for systems with more unequal mass ratio.