Super-Eddington Accretion in Tidal Disruption Events: the Impact of Realistic Fallback Rates on Accretion Rates

TL;DR

This study combines simulations and analytic models to assess how realistic fallback rates influence super-Eddington accretion durations in tidal disruption events, revealing that actual fallback can significantly exceed previous predictions and constraining black hole mass limits.

Contribution

It introduces a simulation-based approach to measure fallback rates and compares them with analytic models, refining understanding of super-Eddington accretion in tidal disruption events.

Findings

Fallback rates can be nearly ten times higher than analytic predictions.

Super-Eddington accretion persists for different durations depending on black hole mass.

New limits on black hole mass for super-Eddington accretion are established.

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 onto 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 onto the black hole evolves with the more accurate fallback rates calculated from the simulations. We find that numerically-simulated fallback rates yield accretion rates onto 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.