Once a giant, (almost) always a giant: Partial Tidal Disruption Events of Giant Stars

TL;DR

This study investigates the aftermath of partial tidal disruption events of giant stars by supermassive black holes, revealing that remnants often return to a giant state and can undergo multiple disruptions, with implications for galactic nuclei observations.

Contribution

The paper uses stellar evolution modeling to show that giant star remnants after partial TDEs can recover their giant structure and undergo successive disruptions, a novel insight into TDE outcomes.

Findings

Remnants return to giant structure with similar radius and slightly higher luminosity.

Remnants can experience multiple partial disruptions, decreasing in mass to 0.6-0.7 solar masses.

Potential identification of low-mass giants as TDE remnants in galactic centers.

Abstract

Tidal disruption events (TDEs) of giant stars by supermassive black holes (SMBH) differ significantly from those of main sequence ones. Most (all for SMBH of more than a~ few times 10^5 m_\odot) giant-TDEs are partial: only a fraction of the envelope is torn apart. The dense stellar core and the rest of the envelope remain intact. In this work, we explore, using the stellar evolution code MESA, the fate of the remnants. We find that after a short period, comparable to the thermal time scale, the remnant returns to a giant structure with a radius comparable to the progenitor giant one, a slightly larger luminosity (as compared with a regular giant with the same mass), and a comparable lifetime until it collapses to a white dwarf. If such a giant with a mass less than approx 0.9 m_\odot is discovered, it can be identified as an outlier - a giant that is too light for the current age of the Universe. If the remnant orbit is not perturbed significantly during the encounter, the remnant will undergo successive partial tidal disruptions until its mass is $0.6-0.7 m_\odot$. We expect a few dozen to a few hundred such remnants in the Galactic nucleus.