The Double Tidal Disruption Event AT 2022dbl Implies That at Least Some "Standard" Optical TDEs are Partial Disruptions

TL;DR

The discovery of a repeating optical-ultraviolet tidal disruption event suggests that many such events may be partial stellar disruptions rather than full disruptions, challenging current models and assumptions about their nature.

Contribution

This paper presents the first observed repeating tidal disruption event, indicating that some optical-ultraviolet TDEs are partial disruptions, which may revise existing theoretical models.

Findings

The event AT 2022dbl was a nearly identical repeat of the first flare.

The repeat event rules out gravitational lensing and unrelated disruptions.

Implication that many optical-ultraviolet TDEs could be partial disruptions.

Abstract

Flares produced following the tidal disruption of stars by supermassive black holes can reveal the properties of the otherwise dormant majority of black holes and the physics of accretion. In the past decade, a class of optical-ultraviolet tidal disruption flares has been discovered whose emission properties do not match theoretical predictions. This has led to extensive efforts to model the dynamics and emission mechanisms of optical-ultraviolet tidal disruptions in order to establish them as probes of supermassive black holes. Here we present the optical-ultraviolet tidal disruption event AT 2022dbl, which showed a nearly identical repetition 700 days after the first flare. Ruling out gravitational lensing and two chance unrelated disruptions, we conclude that at least the first flare represents the partial disruption of a star, possibly captured through the Hills mechanism. Since both flares are typical of the optical-ultraviolet class of tidal disruptions in terms of their radiated energy, temperature, luminosity, and spectral features, it follows that either the entire class are partial rather than full stellar disruptions, contrary to the prevalent assumption, or that some members of the class are partial disruptions, having nearly the same observational characteristics as full disruptions. Whichever option is true, these findings could require revised models for the emission mechanisms of optical-ultraviolet tidal disruption flares and a reassessment of their expected rates.