  Impulsive supernova feedback and non-standard dark matter models, such as
self-interacting dark matter (SIDM), are the two main contenders for the role
of the dominant core formation mechanism at the dwarf galaxy scale. Here we
show that the impulsive supernova cycles that follow episodes of bursty star
formation leave distinct features in the distribution function of stars: groups
of stars with similar ages and metallicities develop overdense shells in phase
space. If cores are formed through supernova feedback, we predict the presence
of such features in star-forming dwarf galaxies with cored host halos. Their
systematic absence would favor alternative dark matter models, such as SIDM, as
the dominant core formation mechanism.
