Quasi-periodic Eruptions from Stellar-mass Black Holes Impacting Accretion Disks in Galactic Nuclei

TL;DR

This paper uses advanced simulations to explore how stellar-mass black holes impacting accretion disks can produce quasi-periodic eruptions in galactic nuclei, explaining observed properties and energy ranges.

Contribution

It introduces a semi-analytical model showing that black hole impacts can generate the full range of observed QPE energies and behaviors, advancing understanding of their origins.

Findings

Stellar impacts produce asymmetric bipolar ejecta with dominant forward outbursts.

Black hole impacts can power the full observed QPE energy range ($10^{44}$-$10^{48}$ erg).

The model accounts for periodicity, asymmetry, durations, and diversity of QPEs.

Abstract

We investigate the origins of quasi-periodic eruptions (QPEs) in galactic nuclei using global three-dimensional meshless finite-mass (MFM) simulations. By modeling stellar and black-hole impactors traversing accretion disks under various inclinations and surface densities, we evaluate their consistency with the observed properties of QPEs. Stellar impacts produce highly asymmetric bipolar ejecta with forward outbursts dominating by over an order of magnitude in energy and luminosity due to the star blocking downstream flow and creating a low-density wake. This shock-compression mechanism often renders backward events unobservable, implying one detectable burst per orbit, and challenging the standard assumption of two bursts. It also fails to explain alternating long-short recurrence patterns and places several sources near or within twice the tidal disruption radius for solar-mass stars, raising severe stability concerns. Whereas a stellar-mass black hole (sBH) gravitationally focuses and heats disk gas extending from its Bondi radius $R_{\rm B}$ to its Hill radius $R_{\rm H}$ during an impact, yielding nearly symmetric ejecta with mild contrasts. This gravitational-drag mechanism generates higher energy budgets at low inclinations due to enhanced mass accumulation. We suggest an ad hoc effective interaction radius $ R_{\rm eff} \simeq 0.5\, R_{\rm B}^{1/3} R_{\rm H}^{2/3} $ to quantify this trend. Our semi-analytical model confirms that sBH-disk collisions can power the full QPE energy range ($10^{44}$-$10^{48}$ erg), naturally accounting for periodicity, asymmetry, durations and diversity.