No model-independent evidence for a peak in binary black hole spin (mis)alignments

TL;DR

This study analyzes gravitational-wave data to investigate the distribution of black hole spin tilts, finding no significant evidence for preferred orientations and confirming a correlation between spin magnitude and mass.

Contribution

It provides a model-independent analysis of black hole spin tilts, challenging previous reports of a peak and emphasizing the difficulty in identifying subpopulations.

Findings

No statistically significant peak in spin tilt distribution.

No reliable correlation between mass and spin tilt.

Confirmed correlation between spin magnitude and mass.

Abstract

The degree of black-hole spin-orbit misalignment ("tilts") in the astrophysical population could be a powerful diagnostic to distinguish between binary formation in isolation, in dynamical environments, or in hierarchical triples. However, robust population-level spin tilt measurements are complicated by model misspecification as well as numerical and Poisson variance, ultimately owing to poor single-event constraints on tilts. Motivated by reports of a possible peak in the spin tilt distribution, we analyze the fourth LIGO-Virgo-KAGRA gravitational-wave transient catalog to test for preferred spin orientations at different black hole masses. We find that a peak in spin tilts is not statistically significant nor model independent. Since the data cannot be used to reliably identify subpopulations based on their spin tilt properties, we also consider a complementary approach: measuring the spin magnitude and tilt distributions at fixed mass scales. We find no confident correlation between mass and spin tilt, but we do confirm a confident correlation between spin magnitude and mass, corroborating recent analyses.