Divergence in mass ratio distributions between low-mass and high-mass coalescing binary black holes

Abstract

The coalescing binary black hole (BBH) systems were likely formed in several channels and the identification of them is a challenging task. Previously, people have found out that at the mass of ∼ 34M there is a distinct Gaussian-like peak superposed on the power-law mass function of the primary components. In this work, with the refined Power Law + Peak primary mass distribution models, we identify a population of BBHs with a much stronger preference for equalmass binaries, which dominates the Peak, for the first time. These BBHs have a pairing function with a β = 8.56 +3.08 −5.62 , or with a σm = 3.14 +4.99 −1.76 M , where σm represents the width of the distribution of m1 − m2 (i.e., the difference between and the primary and secondly masses). The BBHs in the Power Law have a much flatter pairing function with a β = −0.11 +2.48 −1.55 . All these parameter ranges are reported for 90% credibility. Our finding likely points towards the chemically homogeneous evolution channel featured by a high mass ratio for the BBHs with a total mass above ∼ 55M . As shown in our simulation, the increase of the GWTC-3 sample by a factor of several would formally establish the presence of the high q population of massive BBHs.

On the Mass Function of GWTC-2 Binary Black Hole Systems and Their Progenitors

“…On the first, we note that nearby Galactic open stellar clusters show a large fraction of O-type stars born as binaries (Sana et al 2012). Radiation-hydrodynamic simulation suggests fragmentation of rotating gas disk by gravitational instabilities leads to the formation of massive binary stars with similar masses (Krumholz et al 2009;Sana et al 2012;Moe & Di Stefano 2017;Li et al 2022). On the other hand, such mass-correlation is ex- pected to weaken as binary separation becomes large.…”