Classification of Tidal Disruption Events Based on Stellar Orbital Properties

TL;DR

This paper classifies tidal disruption events (TDEs) based on stellar orbital properties, identifying three main types and subclasses, and analyzes their rates and characteristics through high-accuracy N-body simulations.

Contribution

It introduces a classification scheme for TDEs based on orbital eccentricity and derives analytical models for their fallback rates, supported by N-body experiments.

Findings

TDEs are classified into eccentric, parabolic, and hyperbolic types.

Marginally eccentric and hyperbolic TDEs have distinct fallback rate behaviors.

Few TDEs occur in spherical stellar systems, with most being marginally eccentric or hyperbolic.

Abstract

We study the rates of tidal disruption of stars by intermediate-mass to supermassive black holes on bound to unbound orbits by using high-accuracy direct N-body experiments. The approaching stars from the star cluster to the black hole can take three types of orbit: eccentric, parabolic, and hyperbolic orbits. Since the mass fallback rate shows a different variability depending on these orbital types, we can classify tidal disruption events (TDEs) into three main categories: eccentric, parabolic, and hyperbolic TDEs. Respective TDEs are characterized by two critical values of the orbital eccentricity: the lower critical eccentricity is the one below which the stars on eccentric orbits cause the finite, intense accretion, and the higher critical eccentricity above which the stars on hyperbolic orbits cause no accretion. Moreover, we find that the parabolic TDEs are divided into three subclasses: precisely parabolic, marginally eccentric, and marginally hyperbolic TDEs. We analytically derive that the mass fallback rate of the marginally eccentric TDEs can be flatter and slightly higher than the standard fallback rate proportional to $t^{-5/3}$, whereas it can be flatter and lower for the marginally hyperbolic TDEs. We confirm by N-body experiments that only few eccentric, precisely parabolic, and hyperbolic TDEs can occur in a spherical stellar system with a single intermediate-mass to supermassive black hole. A substantial fraction of the stars approaching to the black hole would cause the marginally eccentric or marginally hyperbolic TDEs.