Instability and vertical eccentricity variation in global hydrodynamic disk simulations

TL;DR

This paper investigates how strong eccentricities in astrophysical disks lead to various instabilities and dynamical phenomena through 3D simulations and linear theory, revealing interactions between inertial waves and global modes.

Contribution

It provides a combined analysis of local and global instabilities in eccentric disks, highlighting the nonlinear interaction between inertial waves and low-frequency global modes.

Findings

Inertial waves grow via parametric instability, matching local theory predictions.

Global low-frequency modes are excited and interact with inertial turbulence.

Eccentricity variations can cause vertical corrugation of the disk.

Abstract

Many dynamical interactions can induce eccentricities in astrophysical accretion disks. Disk eccentricities in turn seed a variety of instabilities, even in ideal hydrodynamics. We use 3D nonlinear simulations and 2+1D linear calculations to characterize local and global instabilities in strongly distorted disks. On local scales, our simulations show the growth of parametrically excited inertial waves, which drive wave turbulence. The inertial waves' growth rates and localizations agree with the predictions of local theory. On global scales, we observe the growth of a separate family of low-frequency, vertically structured modes that compare favorably with eigenmodes computed from the linear theory of an eccentric background state. These low-frequency modes interact nonlinearly with the inertial wave turbulence driven by parametric instability, and they induce variation in eccentricity profiles that are initially uniform in the vertical direction. Extrapolating from our vertically local framework, we postulate that these secondary distortions may correspond to the corrugation of an initially planar eccentric disk. Our simulations demonstrate that strong disk eccentricities drive numerous dynamical phenomena even in a purely hydrodynamic, Newtonian framework.