A Quasi-Stationary Twisted Disk Formed as a Result of a Tidal Disruption Event

[摘要] In this note we briefly review the main results of our recent study of the formation of misaligned accretion disks after the tidal disruption of stars by rotating supermassive black holes. Since the accretion rates in such disks initially exceed the Eddington limit they are initially advection dominated. Assuming the α model for the disk viscosity implies that the disk can become thermally unstable when the accretion rate is comparable to, or smaller than, the Eddington value, while still being radiation pressure dominated. It then undergoes cyclic transitions between high and low states. During these transitions the aspect ratio varies from ~1 to ~10 −3 , which is reflected in changes in the degree of disk misalignment at the stream impact location. For maximal black hole rotation and sufiociently large values of the viscosity parameter, α ≳ 0.01–0.1, the ratio of the disk inclination to that of the initial stellar orbit is estimated to be 0.1–0.2 in the advection dominated state, while reaching order unity in the low state. Misalignment decreases with decrease of α , but increases as the black hole rotation parameter decreases. Thus, it is always significant when the latter is small.

[关键词] accretion disks;hydrodynamics;galaxies supermassive black holes