Neutrino Flavor Conversion Shapes the Rate of Failed Core-collapse Supernovae

The relative rate of neutron stars and black holes produced by the collapse of massive stars is highly uncertain. We simulate the stellar collapse of $195$ progenitors with masses between $9M_{\odot }$ and $120M_{\odot }$, incorporating a schematic treatment of neutrino flavor conversion. We find that flavor transformation reshapes the explodability of massive stars-especially in the $16$-$30M_{\odot }$ mass range-and modifies the compact remnant mass distribution. Our findings identify neutrino flavor conversion as a fundamental ingredient in predicting neutron star and black hole populations, while naturally easing the red-supergiant and the supernova-rate problems, as well as reconciling theoretical expectations with the low-mass tail of the observed neutron star mass distribution.