Looking To The Horizon: Probing Evolution in the Black Hole Spectrum With Gravitational Wave Catalogs

TL;DR

This paper reconstructs the black hole binary merger rate over cosmic time using gravitational wave data, finding no strong evidence for mass evolution with redshift but noting potential trends that require more data to confirm.

Contribution

It introduces a novel iterative kernel density estimation method to reconstruct the BBH merger rate considering selection effects and explores mass evolution with redshift.

Findings

No significant evidence for BBH mass evolution with redshift.

Possible trends: increasing merger rate for high-mass BHs, decreasing for lower-mass BHs.

Current data is sparse; future detectors needed for clearer insights.

Abstract

The population of black holes observed via gravitational waves currently covers the local universe up to a redshift $z\lesssim 1$, for the most massive merging binaries, or $z\lesssim 0.25$ for low-mass BH binaries (BBH). Evolution of the BBH mass spectrum over cosmic time will be a significant probe of formation channels and environments. We demonstrate a reconstruction of the BBH merger rate, allowing for general dependence on binary masses and luminosity distance or redshift and accounting for selection effects, via iterative kernel density estimation (KDE) with optimized multidimensional bandwidths. Performing such reconstructions under a range of detailed assumptions, we see no significant evidence for the evolution of BBH masses with redshift, over the range where detected events are available. At most, possible trends towards increasing merger rate with redshift for primary masses $m_1\gtrsim 50\,M_\odot$, or towards decreasing merger rate with redshift for primary masses $m_1 \lesssim 40 M\odot$ may be supported. We compare these findings with previous investigations and caution against over-interpreting the current, sparse, data. Significantly upgraded detectors and/or facilities, and longer observing times, are required to harness any correlations of the BBH mass distribution with redshift.