Radiation-hydrodynamics of star-disc collisions: From system parameters to outflows and lightcurves
Abstract
Quasi-periodic eruptions (QPEs) are nuclear transients producing bright, repeating soft X-ray flares superimposed on quiescent emission. A promising interpretation is that they are powered by star-disc collisions, in which a star crosses an accretion disc around a supermassive black hole, drives shocks, and launches dense outflows from which radiation emerges. We present a systematic study of star-disc collisions, linking the physical parameters of the collision to the resulting outflows and emerging bolometric luminosities. We perform three-dimensional local radiation-hydrodynamics simulations, varying the disc surface density and vertical density profiles, stellar velocity and radius, and local collision angle. We focus on the regime where the star remains unperturbed by the collision. We find that variations in stellar velocity and accretion disc surface density leave the bow shock and outflow morphology largely unchanged. Faster stars produce brighter flares, while denser discs mainly increase the flare duration. Increasing the stellar radius increases the momentum of the forward outflow and produces brighter and longer flares. More centrally concentrated discs yield brighter and shorter flares because radiation escapes more efficiently through outer low-density layers. More oblique crossings reduce the momentum and luminosity asymmetry of two outflows, and lengthen the flares. We provide empirical scalings of the peak luminosity and flare duration with the individual system parameters and apply them to GSN 069. The best candidate solutions favour a star with a radius ∼ R⊙ on a retrograde orbit, colliding with a dense post-TDE disc with a vertically concentrated density profile. Our findings suggest that specific combinations of system parameters can reproduce characteristic flare amplitudes, durations, duty cycles, and strong-weak flare patterns observed in QPE sources.
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BibTeX
@misc{jankovic2026radiationhydrodynamics,
title = {{Radiation-hydrodynamics of star-disc collisions: From system parameters to outflows and lightcurves}},
author = {Taj Jankovič and Sergey Karpov and Michal Zajaček and Vladimír Karas and Marzena Śniegowska},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.05508},
eprint = {2607.05508},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.05508},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Radiation-hydrodynamics of star-disc collisions: From system parameters to outflows and lightcurves
AU - Taj Jankovič
AU - Sergey Karpov
AU - Michal Zajaček
AU - Vladimír Karas
AU - Marzena Śniegowska
PY - 2026
DA - 2026/09/30
PB - arXiv
DO - 10.48550/arxiv.2607.05508
UR - https://arxiv.org/abs/2607.05508
AB - Quasi-periodic eruptions (QPEs) are nuclear transients producing bright, repeating soft X-ray flares superimposed on quiescent emission. A promising interpretation is that they are powered by star-disc collisions, in which a star crosses an accretion disc around a supermassive black hole, drives shocks, and launches dense outflows from which radiation emerges. We present a systematic study of star-disc collisions, linking the physical parameters of the collision to the resulting outflows and emerging bolometric luminosities. We perform three-dimensional local radiation-hydrodynamics simulations, varying the disc surface density and vertical density profiles, stellar velocity and radius, and local collision angle. We focus on the regime where the star remains unperturbed by the collision. We find that variations in stellar velocity and accretion disc surface density leave the bow shock and outflow morphology largely unchanged. Faster stars produce brighter flares, while denser discs mainly increase the flare duration. Increasing the stellar radius increases the momentum of the forward outflow and produces brighter and longer flares. More centrally concentrated discs yield brighter and shorter flares because radiation escapes more efficiently through outer low-density layers. More oblique crossings reduce the momentum and luminosity asymmetry of two outflows, and lengthen the flares. We provide empirical scalings of the peak luminosity and flare duration with the individual system parameters and apply them to GSN 069. The best candidate solutions favour a star with a radius ∼ R_⊙ on a retrograde orbit, colliding with a dense post-TDE disc with a vertically concentrated density profile. Our findings suggest that specific combinations of system parameters can reproduce characteristic flare amplitudes, durations, duty cycles, and strong-weak flare patterns observed in QPE sources.
ER -