The Aftermath of Tidal Disruption: The Dynamics of Thin Gas Streams

We study the hydrodynamics of the gas stream created from the debris of a star disrupted by the tides of a massive black hole. The circularization and accretion of the debris orbits depends on the transverse structure of the stream because the stream cross section determines the effectiveness of energy and angular momentum transfers. The transverse structure is modified by crossing points in the stream where orbits are focused across the stream center or through the orbital plane, the velocity shear across the stream, self-gravity (in the more distant encounters), recombination, shocks, and shear viscosity. During the first several orbits it is insensitive to the ambient medium and the luminosity of the active galactic nucleus. Stream-stream collisions may have a weak effect on the orbits because of Lense-Thirring precession, mismatched geometric cross sections, and the kinematics of collisions.