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

TL;DR

This study uses 3D general relativistic smoothed particle hydrodynamics simulations to explore how stars disrupted by rotating supermassive black holes form accretion discs, considering relativistic effects, inclination, and radiative cooling.

Contribution

It provides new insights into disc formation mechanisms, including relativistic precession effects and cooling impacts, in tidal disruption events involving Kerr black holes.

Findings

Stream-stream collisions rapidly circularize disrupted material into a disc.

Inclined orbits cause short delays in disc formation due to Lense-Thirring precession.

Energy dissipation rates vary from 10^{45} to 10^{47} erg s^{-1} depending on encounter depth.

Abstract

We perform 3D general relativistic smoothed particle hydrodynamics (GRSPH) simulations of tidal disruption events involving 1 $M_\odot$ stars and $10^6 M_\odot$ 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 $\sim10^{45}$ erg s$^{-1}$ for stars disrupted at the tidal radius, and up to $\sim10^{47}$ erg s$^{-1}$ for deep encounters.