Disc formation from tidal disruption of stars on eccentric orbits by Kerr black holes using GRSPH

Abstract: We perform 3D general relativistic smoothed particle hydrodynamics (GRSPH) simulations of tidal disruption events involving 1 $M_\odot$ stars and $10⁶ M_\odot$ rotating supermassive black holes. We consider stars on initially elliptical orbits both in, and inclined to, the black hole equatorial plane. We confirm that stream-stream collisions caused by relativistic apsidal precession rapidly circularise the disrupted material into a disc. For inclined trajectories we find that nodal precession induced by the black hole spin (i.e. Lense-Thirring precession) inhibits stream-stream collisions only in the first orbit, merely causing a short delay in forming a disc, which is inclined to the black hole equatorial plane. We also investigate the effect of radiative cooling on the remnant disc structure. We find that with no cooling a thick, extended, slowly precessing torus is formed, with a radial extent of 5 au (for orbits with a high penetration factor). Radiatively efficient cooling produces a narrow, rapidly precessing ring close to pericentre. We plot the energy dissipation rate, which tracks the pancake shock, stream-stream collisions and viscosity. We compare this to the effective luminosity due to accretion onto the black hole. We find energy dissipation rates of $\sim10<sup>{45}$ erg s$<sup>{-1}$ for stars disrupted at the tidal radius, and up to $\sim10<sup>{47}$ erg s$<sup>{-1}$ for deep encounters.