  Dark matter direct detection experiments have poor sensitivity to a galactic
population of dark matter with mass below the GeV scale. However, such dark
matter can be produced copiously in supernovae. Since this thermally-produced
population is much hotter than the galactic dark matter, it can be observed
with direct detection experiments. In this paper, we focus on a dark sector
with fermion dark matter and a heavy dark photon as a specific example. We
first extend existing supernova cooling constraints on this model to the regime
of strong coupling where the dark matter becomes diffusively trapped in the
supernova. Then, using the fact that even outside these cooling constraints the
diffuse galactic flux of these dark sector particles can still be large, we
show that this flux is detectable in direct detection experiments such as
current and next-generation liquid xenon detectors. As a result, due to
supernova production, light dark matter has the potential to be discovered over
many orders of magnitude of mass and coupling.
