Super-Eddington accretion in tidal disruption events: the impactof realistic fallback rates on accretion rates

Abstract

After the tidal disruption of a star by a massive black hole, disrupted stellar debris can fall back to the hole at a rate significantly exceeding its Eddington limit. To understand how black hole mass affects the duration of super-Eddington accretion in tidal disruption events, we first run a suite of simulations of the disruption of a Solar-like star by a supermassive black hole of varying mass to directly measure the fallback rate on to the hole, and we compare these fallback rates to the analytic predictions of the 'frozen-in' model. Then, adopting a zero-Bernoulli accretion flow as an analytic prescription for the accretion flow around the hole, we investigate how the accretion rate on to the black hole evolves with the more accurate fallback rates calculated from the simulations. We find that numerically simulated fallback rates yield accretion rates on to the hole that can, depending on the black hole mass, be nearly an order of magnitude larger than those predicted by the frozen-in approximation. Our results place new limits on the maximum black hole mass for which super-Eddington accretion occurs in tidal disruption events.