Radiation hydrodynamics of supernova shock breakouts

The first powerful burst of photon radiation in a supernova appears when the shock front is a few photon mean-free paths below the star photosphere. This is called “shock breakout” and it is the first observable event after the neutrino and gravitational wave bursts in core-collapsing supernovae. Any early information about collapse is vitally important for understanding the physics of explosion, constraining speed of neutrino propagation etc. Direct observations of shock breakouts have been carried out in a few supernovae. We discuss some puzzles related to those objects. Finally, we describe our current understanding of the most luminous (hyper-)supernovae. Their long living radiative shocks pause many interesting problems in numerical and laboratory astrophysics and may have important applications in cosmology.