This is a talk given at lunch time, usually in the conference room at noon.
Shock waves are ubiquitous in high-energy astrophysics. The first electromagnetic signal observed in different types of stellar explosions, such as supernovae and gamma ray bursts, is released upon emergence of a shock wave from an opaque stellar envelope, enshrouding a central source.
Nearly a quarter of all massive stars will merge with a companion during their lifetimes. This coalescence is preceded by a contact phase, which, while expected to be common, is poorly understood.