We investigate the impact of millicharged particles (MCPs) on massive stars undergoing pulsational pair-instability supernovae and on the location of the lower edge of the black hole mass gap. We find that energy losses due to MCP emission weaken the pulsations, allowing the star to retain more mass and thereby shifting the lower edge of the mass gap to higher black hole masses. The mass gap is sensitive to a region of MCP parameter space with masses 35keV≲mχ≲200keV and charges 10−10≲q≲10−9, which remains unconstrained by existing astrophysical probes. If confirmed, recent gravitational wave observations placing the lower edge of the mass gap near 45M⊙ would translate directly into bounds on this parameter space.
@article{arxiv.2604.02413,
title = {The Black Hole Mass Gap as a New Probe of Millicharged Particles},
author = {Damiano F. G. Fiorillo and Giuseppe Lucente and Jeremy Sakstein and Edoardo Vitagliano and Matteo Cantiello},
journal= {arXiv preprint arXiv:2604.02413},
year = {2026}
}