Gravitational-wave observations reveal that the rate of merging black holes drops by $\sim 2$ orders of magnitude from component masses $\sim 10M_{\odot }$ to $\sim 15M_{\odot }$. The increased compactness of the black hole progenitor cores may contribute to the $\sim 10M_{\odot }$ 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 $10M_{\odot }$. 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 $10M_{\odot }$, 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 $\sim 16M_{\odot }$ before falling at higher masses. Our results reveal structure in the mass distribution in the $10-20M_{\odot }$ range, with rate changes of multiple orders of magnitude across a few solar masses, consistent with a distinct population of failed-supernova black holes. These conclusions persist in the latest GWTC-5.0 catalog.

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• Formation & evolution of stars & galaxies
• Astronomical black holes
• Gravitational wave detectors