  Many theories of dark matter (DM) predict that DM particles can be captured
by stars via scattering on ordinary matter. They subsequently condense into a
DM core close to the center of the star and eventually annihilate. In this
work, we trace DM capture and annihilation rates throughout the life of a
massive star and show that this evolution culminates in an intense annihilation
burst coincident with the death of the star in a core collapse supernova. The
reason is that, along with the stellar interior, also its DM core heats up and
contracts, so that the DM density increases rapidly during the final stages of
stellar evolution. We argue that, counterintuitively, the annihilation burst is
more intense if DM annihilation is a $p$-wave process than for $s$-wave
annihilation because in the former case, more DM particles survive until the
supernova. If among the DM annihilation products are particles like dark
photons that can escape the exploding star and decay to Standard Model
particles later, the annihilation burst results in a flash of gamma rays
accompanying the supernova. For a galactic supernova, this "dark gamma ray
burst" may be observable in CTA.
