Emergent structure in the binary black hole mass distribution and implications for population-based cosmology

TL;DR

This paper reconstructs the black hole mass distribution from gravitational wave data, revealing structure that influences cosmological measurements and proposing methods to improve robustness in population-based cosmology.

Contribution

It introduces an agnostic B-spline method to identify mass features and a subpopulation approach to reduce systematic uncertainties in cosmological inference.

Findings

Identified multiple mass features in GWTC-4.0 data.

Found evidence of a logarithmic hierarchy in black hole populations.

Demonstrated impact of mass structure on Hubble constant measurements.

Abstract

Gravitational waves provide a powerful probe of both the astrophysical processes driving black hole mergers and the dynamics of the Universe, but these measurements rely on accurately inferring the unknown underlying population. We perform an agnostic reconstruction of the primary mass distribution using B-splines, characterising the emergence of structure with increasing model complexity. Using the latest gravitational-wave transient catalog, GWTC-4.0, we identify multiple mass features and find evidence suggesting a logarithmic hierarchy in the population. We show that this structure directly impacts measurements of the Hubble constant, primarily through features at the population boundaries. Finally, we introduce an approach that isolates a subpopulation of low-mass events to mitigate modelling systematics, providing a promising path toward robust population-based cosmology with future datasets.