Repeating Nuclear Transients from Repeating Partial Tidal Disruption Events

TL;DR

This paper investigates the dynamics and stability of stars undergoing repeated partial tidal disruptions by supermassive black holes, explaining recurring nuclear transients and their observational signatures.

Contribution

It provides hydrodynamical simulations and analytical models to understand the long-term evolution of stars in rpTDEs and predicts their survival or destruction based on stellar type.

Findings

High-mass stars survive multiple mass-loss events.

Low-mass stars are destroyed within a few orbits.

Implications for observed repeating transients like ASASSN-14ko.

Abstract

Extragalactic nuclear transients that exhibit repeating outbursts can be modeled as the repeated dynamical interaction between bound stars and supermassive black holes (SMBHs). A subset of these transients, with recurrence timescales of months-to-years, have been explained as accretion flares from the repeated tidal stripping of a star by an SMBH, in a repeating partial tidal disruption event (rpTDE). We outline the scope of the rpTDE model and discuss hydrodynamical simulations and analytical predictions for the stability of stars undergoing repeated mass loss, and the long-term evolution of these flares as a function of stellar type and orbital parameters. Our findings demonstrate that high-mass and centrally concentrated stars undergo negligible changes in structure in response to small amounts ($\sim 1-10\% M_\star$) of mass loss, and can survive many mass-stripping encounters with an SMBH. Contrarily, low-mass and less evolved stars are unstable to mass loss, and would be destroyed within a few orbits. We discuss the implications of these results for constraining the stellar type and orbital parameters of observed sources, such as ASASSN-14ko, for which $\gtrsim 20$ flares have been observed, and AT2020vdq, which exhibits a second flare that is brighter than its primary outburst.