Probing orbits of stellar mass objects deep in galactic nuclei with quasi-periodic eruptions

TL;DR

This paper proposes that quasi-periodic eruptions in galactic nuclei result from collisions between a TDE-formed accretion disk and stellar mass objects orbiting SMBHs, offering a new way to probe stellar orbits near black holes.

Contribution

It introduces an EMRI+TDE disk model explaining QPEs and demonstrates how QPE observations can reveal stellar orbits and EMRI formation near SMBHs.

Findings

QPEs can be caused by collisions between TDE disks and stellar objects.

The model suggests low-eccentricity EMRIs with semi-major axes of hundreds of gravitational radii.

Application to GSN 069 supports the wet EMRI formation channel.

Abstract

Quasi-periodic eruptions (QPEs) are intense repeating soft X-ray bursts with recurrence times about a few to ten hours from nearby galactic nuclei. The origin of QPEs is still unclear. In this work, we investigated the extreme mass ratio inspiral (EMRI) + accretion disk model, where the disk is formed from a previous tidal disruption event (TDE). In this EMRI+TDE disk model, the QPEs are the result of collisions between a TDE disk and a stellar mass object (a stellar mass black hole or a main sequence star) orbiting around a supermassive black hole (SMBH) in galactic nuclei. If this interpretation is correct, QPEs will be invaluable in probing the orbits of stellar mass objects in the vicinity of SMBHs, and further inferring the formation of EMRIs which are one of the primary targets of spaceborne gravitational wave missions. Taking GSN 069 as an example, we find the EMRI wherein is of low eccentricity ($e<0.1$ at 3-$\sigma$ confidence level) and semi-major axis about $O(10^2)$ gravitational radii of the central SMBH, which is consistent with the prediction of the wet EMRI formation channel, while incompatible with alternatives.