Adiabatic Shocks in Accretion Flows

Abstract

Accretion flows onto compact astronomical sources are likely to be supersonic, and shock waves may therefore be common in such flows. Plasma passing through a shock front will be compressed and heated according to the jump conditions across the shock discontinuity. Shocks in accretion flows may therefore have important consequences for the flow structure and emission characteristics. The equations governing adiabatic (nonradiative) shocks in relativistic plasmas are presented. Relativistically correct equations of state are used that include the effects of radiation pressure and energy density, and pair equilibria are calculated for the postshock flow. Postshock states are determined for accretion flows with typical accretion-driven astronomical sources, and possible dynamics of the postshock flow are suggested. In particular, we find that cool, optically thick accretion flows undergoing shocks may become radiation or pair dominated and that the postshock plasma will likely become optically thin before returning to steady state conditions.