Collapsars: Gamma -ray bursts and asymmetric supernovae

The fate of rotating massive stars which form black holes during, or soon after, core collapse is studied by means of two-dimensional hydrodynamics simulations. In rapidly rotating stars, an accretion disk forms as the star collapses into a black hole created by the implosion of its core. Rapid accretion at 10-4--10-1 solar masses per second of stellar matter through an accretion disk releases gravitational binding energy which can power a variety of stellar explosions with diverse observational signatures. These include classical gamma-ray bursts and energetic, asymmetic supernovae. The main result of this thesis is that prompt black hole formation in a rapidly rotating helium star can make classical gamma-ray bursts of the long duration variety.