A Star's Death by a Thousand Cuts: The Runaway Periodic Eruptions of AT2023uqm

TL;DR

AT2023uqm is a confirmed periodic tidal disruption event showing exponential energy increase and double-peaked flares, providing new insights into star-black hole interactions and stellar destruction processes.

Contribution

This paper reports the discovery and detailed analysis of AT2023uqm, the second confirmed periodic rpTDE, highlighting its unique flare structure and implications for stellar disruption models.

Findings

AT2023uqm exhibits at least five periodic optical flares.

Flares show a nearly exponential energy increase, indicating a runaway process.

Flares display a double-peaked structure, suggesting complex fallback or collision dynamics.

Abstract

Stars on bound orbits around a supermassive black hole may undergo repeated partial tidal disruption events (rpTDEs), producing periodic flares. While several candidates have been suggested, definitive confirmation of these events remains elusive. We report the discovery of AT2023uqm, a nuclear transient that has exhibited at least five periodic optical flares, making it only the second confirmed case of periodicity after ASASSN-14ko. Uniquely, the flares from AT2023uqm show a nearly exponential increase in energy--a "runaway" phenomenon signaling the star's progressive destruction. This behavior is consistent with rpTDEs of low-mass, main-sequence stars or evolved giant stars. Multiwavelength observations and spectroscopic analysis of the two most recent flares reinforce its interpretation as an rpTDE. Intriguingly, each flare displays a similar double-peaked structure, potentially originating from a double-peaked mass fallback rate or two discrete collisions per orbit. The extreme ratio of peak separation to orbital period draws attention to the possibility of a giant star being disrupted, which could be distinguished from a low-mass main-sequence star by its future mass-loss evolution. Our analysis demonstrates the power of rpTDEs to probe the properties of disrupted stars and the physical processes of tidal disruption, though it is currently limited by our knowledge of these events. AT2023uqm emerges as the most compelling rpTDE thus far, serving as a crucial framework for modeling and understanding these phenomena.