The binary black hole spin distribution likely broadens with redshift

TL;DR

This study analyzes gravitational wave data to show that the distribution of black hole spins broadens with increasing redshift, suggesting evolving astrophysical processes over cosmic time.

Contribution

It introduces a hierarchical model that accounts for correlations between black hole spin, mass, and redshift, revealing a redshift-dependent spin distribution.

Findings

The effective spin distribution widens with redshift at 98.6% credibility.

The trend is robust across various models and simulations.

Possible link to evolving natal black hole spins with redshift.

Abstract

The population-level distributions of the masses, spins, and redshifts of binary black holes (BBHs) observed using gravitational waves can shed light on how these systems form and evolve. Because of the complex astrophysical processes shaping the inferred BBH population, models allowing for correlations among these parameters will be necessary to fully characterize these sources. We hierarchically analyze the BBH population detected by LIGO and Virgo with a model allowing for correlations between the effective aligned spin and the primary mass and redshift. We find that the width of the effective spin distribution grows with redshift at 98.6% credibility. We determine this trend to be robust under the application of several alternative models and additionally verify that such a correlation is unlikely to be spuriously introduced using a simulated population. We discuss the possibility that this correlation could be due to a change in the natal black hole spin distribution with redshift.