AI Insight
This paper demonstrates that grid-based simulations of asymmetric accretion discs produce different stability outcomes depending on the choice of reference frame (stellocentric versus barycentric). The authors identify a new type of instability called "bracket modes" that arise from boundary conditions in the simulation domain, showing that the same disc can appear stable in one frame but unstable in another. This frame-dependence occurs because the boundaries of finite simulation domains change location depending on the reference frame chosen, particularly when the central object moves in response to asymmetric mass distributions in the disc.
Why it matters
This finding challenges the reliability of current numerical simulations used to study planet-disc interactions and asymmetric disc structures. The results suggest that many existing simulation results may need reinterpretation and that new computational methods are needed to properly account for the gravitational feedback between discs and their central objects.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: If the mass distribution within an accretion disc is asymmetric, it will exert a gravitational pull on its central object. The central object must then move away from the origin of the reference frame, resulting in atypical gravitational pulls on the disc. The goal of the present series of papers is to investigate the stability of this feedback loop. In this first paper, we report a surprising finding: the choice of reference frame affects the number and nature of the waves and instabilities contained in the analytical equations. To show this, we use a simple example: the modes discovered by Sanchez et al. (2025, Appendix A.3). We provide the first analytical description of those modes, we explain their physical mechanism, and propose to call them ‘bracket modes’ because they arise from the bracket side of an integration by parts. We show that the same disc can be stable in the stellocentric reference frame but unstable in the barycentric reference frame. This is because the boundaries of the simulation domain are frame-dependent. To avoid this, one must model the entire disc all the way from the central cavity to the outer edge. But this is prohibitively expensive, and some discs do not have a central cavity anyway. Our results suggest that extreme caution is required when interpreting simulations of asymmetric discs, and that our community may not have the tools to model the reflex motion of the central object yet.
Source: Reflex instabilities I: Boundaries makes grid-based disc simulations frame-dependent