The Eccentric Nature of Eccentric Tidal Disruption Events

TL;DR

This study uses hydrodynamic simulations to explore how the eccentricity of stellar orbits affects the debris fallback and reformation in tidal disruption events by supermassive black holes, revealing complex fallback structures and star reformation.

Contribution

It provides new insights into the impact of orbital eccentricity on debris fallback and star reformation in tidal disruption events, which was not thoroughly studied before.

Findings

Eccentricity influences fallback curve structure, creating a three-peak pattern for e < 0.98.

Stars can reform after initial disruption for e > 1.06.

Eccentricity affects long-term debris evolution and potential observational signatures.

Abstract

Upon entering the tidal sphere of a supermassive black hole, a star is ripped apart by tides and transformed into a stream of debris. The ultimate fate of that debris, and the properties of the bright flare that is produced and observed, depends on a number of parameters, including the energy of the center of mass of the original star. Here we present the results of a set of smoothed particle hydrodynamics simulations in which a $1~M_\odot $, $\gamma = 5/3$ polytrope is disrupted by a $10^6 ~M_\odot$ supermassive black hole. Each simulation has a pericenter distance of $r_{\rm p} = r_{\rm t}$ (i.e., $\beta \equiv r_{\rm t}/r_{\rm p} = 1$ with $r_{\rm t}$ the tidal radius), and we vary the eccentricity $e$ of the stellar orbit from $e = 0.8$ up to $e = 1.20$ and study the nature of the fallback of debris onto the black hole and the long-term fate of the unbound material. For simulations with eccentricities $e \lesssim 0.98$, the fallback curve has a distinct, three-peak structure that is induced by self-gravity. For simulations with eccentricities $e \gtrsim 1.06$, the core of the disrupted star reforms following its initial disruption. Our results have implications for, e.g., tidal disruption events produced by supermassive black hole binaries.