AST 95-29175 PI: Mitchell Begelman Theoretical Investigations of Relativistic Jets and Extragalactic Radio Sources Clues to the nature of relativistic jets in extragalactic radio sources--to their speed, composition, and internal energy content--can be obtained by studying how they respond to disturbances. Such disturbances are provided by Nature, in the form of shocks, interactions with the ambient radiation field, and hydrodynamic instabilities. Observations, at all wavelengths from radio to gamma-rays, are now providing detailed information about the morphologies, motions, and radiative properties of these disturbances. This investigation is aimed at relating the physical character of these disturbances to their observational signatures, and determining how the interactions of jets with the gas surrounding it in an evolving cocoon affect the evolution and appearance of extragalactic radio sources. Models will be developed for particle acceleration at relativistic oblique shocks. The effects of radiation drag on the magnetic acceleration of jets, and whether the drag can trigger shocks, will be investigated.