GWTC-4.0: Population Properties of Merging Compact Binaries

TL;DR

This paper analyzes the population properties of merging compact binaries using gravitational-wave data, revealing features in mass and spin distributions, and providing insights into their formation channels and evolutionary history.

Contribution

It presents the first detailed analysis of the population properties of 158 merging compact objects from GWTC-4.0, including mass, spin, and formation channel inferences.

Findings

Mass distribution shows multiple features at 10, 20, and 35 solar masses.

Black hole spins are generally non-extremal and aligned with the orbit.

A significant fraction of binaries have negative effective spins, indicating diverse formation channels.

Abstract

We detail the population properties of merging compact objects using 158 mergers from the cumulative Gravitational-Wave Transient Catalog 4.0, which includes three types of binary mergers: binary neutron star, neutron star--black hole binary, and binary black hole mergers. We resolve multiple over- and under-densities in the black hole mass distribution: features persist at primary masses of $10\,M_\odot$ and $35\,M_\odot$ with a possible third feature at $\sim 20\,M_\odot$. These are departures from an otherwise power-law-like continuum that steepens above $35\,M_\odot$. Binary black holes with primary masses near $10\,M_\odot$ are more likely to have less massive secondaries, with a mass ratio distribution peaking at $q = 0.74^{+0.13}_{-0.13}$, potentially a signature of stable mass transfer during binary evolution. Black hole spins are inferred to be non-extremal, with 90\% of black holes having $\chi < 0.57$, and preferentially aligned with binary orbits, implying many merging binaries form in isolation. However, we find a significant fraction, 0.24-0.42, of binaries have negative effective inspiral spins, suggesting many could be formed dynamically in gas-free environments. We find evidence for correlation between effective inspiral spin and mass ratio, though it is unclear if this is driven by variation in the mode of the distribution or the width. (Abridged)