Low-mass failed supernovae and the $10\,M_{\odot}$ peak in the merging black hole mass distribution

TL;DR

This study analyzes gravitational-wave data to identify a distinct population of failed-supernova black holes around 10 solar masses, revealing complex structure in the black hole mass distribution.

Contribution

It extends previous work by identifying a separate failed-supernova black hole subpopulation with a narrow mass range and detailed rate distribution using the latest GWTC-4.0 data.

Findings

Confirmed a strong peak at 10 M_sun in primary mass distribution.

Found a sharp drop in rate for masses between 12 and 16 M_sun.

Detected structure indicating a distinct failed-supernova black hole population.

Abstract

Gravitational-wave observations reveal that the rate of merging black holes drops by $\sim2$ orders of magnitude from component masses $\sim 10\,M_{\odot}$ to $\sim 15\,M_{\odot}$. The increased compactness of the black hole progenitor cores may contribute to the $\sim 10\,M_{\odot}$ overdensity, but cannot fully explain the rate difference. In this paper, we consider the possibility that the overdensity is reinforced by supernova processes that result in efficient black hole formation from direct collapse in a narrow range around $10\, M_{\odot}$. We extend previous studies by considering a distinct subpopulation of failed-supernovae black holes, possibly separated by a gap in the primary mass distribution from the rest of the population. Using 153 observations from the latest GWTC-4.0 catalog, we confirm a strong peak in the primary mass distribution at $10\,M_{\odot}$, with a peak rate density of $7.36_{-3.11}^{+6.35}$ $M_{\odot}^{-1}\mathrm{yr}^{-1} \mathrm{Gpc}^{-3}$. The rate drops sharply and becomes consistent with zero at the 90 % level for primary mass $m_1\in (12.0, 16.1)\, M_{\odot}$, then rises again to confidently nonzero values above $\sim 16\,M_{\odot}$ before falling at higher masses. Our results reveal structure in the mass distribution in the $10-20\,M_{\odot}$ range, with rate changes of multiple orders of magnitude across a few solar masses, consistent with a distinct population of failed-supernova black holes.