Quasi--Periodic Eruptions from Galaxy Nuclei

TL;DR

This paper proposes that quasi-periodic eruptions in galaxy nuclei are caused by white dwarfs in eccentric orbits around black holes, with evolution driven by gravitational wave emission, and discusses their stability and observational implications.

Contribution

It introduces a model linking QPEs to white dwarf accretion in eccentric orbits and clarifies the stability of mass transfer in these systems.

Findings

QPEs are consistent with white dwarf accretion in eccentric orbits.

Mass transfer in QPE systems is always highly stable.

Eruption properties evolve as the white dwarf orbit decays.

Abstract

I consider quasi--periodic eruptions (QPEs) from galaxy nuclei. All the known cases fit naturally into a picture of accretion from white dwarfs (WDs) in highly eccentric orbits about the central black holes which decay through gravitational wave emission. I argue that ESO 243-39 HLX--1 is a QPE source at an earlier stages of this evolution, with correspondingly a longer period, more extreme eccentricity, and significantly more massive WD donor. I show explicitly that mass transfer in QPE systems is always highly stable, despite recent claims to the contrary in the literature. This stability may explain the alternating long--short eruptions seen in some QPE sources. As the WD orbit decays, the eruptions occupy larger fractions of the orbit and become brighter, making searches for quasi--periodicities in bright low--mass galaxy nuclei potentially fruitful.