Pushing the limits of eccentricity in planet-disc interactions

TL;DR

This paper validates a linear model for eccentric planet-disc interactions through hydrodynamic simulations, revealing its accuracy across various eccentricities and disc conditions, and highlighting nonlinear effects like shocks and horseshoe drags.

Contribution

It provides a comprehensive comparison between linear theory and simulations for highly eccentric perturbers, establishing a benchmark and cautioning against simplistic fitting functions.

Findings

Strong agreement between simulations and linear theory for eccentricities up to local aspect ratio.

Identification of torque reversal phenomena at high eccentricities.

Observation of nonlinear shock effects and coorbital dynamics varying with eccentricity.

Abstract

Modelling the gravitational interaction between an eccentric perturber and a differentially shearing gas disc is a longstanding problem with various astrophysical applications, ranging from the evolution of planetary systems to the migration of black holes embedded in AGN discs. Recent work has advanced a global, linear, modal approach for calculating the excited wake and the resulting feedback on the perturber's orbital evolution. In this work we perform a complementary suite of targeted hydrodynamic simulations to test this linear framework across a range of disc temperature and density profiles. In particular, we push from circular orbits to highly eccentric trajectories for which the perturber moves supersonically with respect to the background gas. We find remarkable agreement between our simulations and the linear methodology across a range of diagnostics -- lending support to the predicted wake morphologies, complex radial torque density profiles, and torque reversal phenomena, which occur when the eccentricity exceeds the local aspect ratio. In contrast, comparison with previous fitting functions exposes noticeable discrepancies, cautioning against their indiscriminate use in studies which explore a wide range of perturber eccentricities, in varied disc structures. Our simulations also probe the fundamentally nonlinear effects of shock induced angular momentum deposition and coorbital horseshoe drags, which exhibit clear variations with eccentricity. Finally, this careful comparison between linear theory and numerics provides a detailed benchmark for planet-disc interaction problems and therefore we have provided a repository of our linear calculations for use as a rigorous test of future numerical investigations.