Instability of high-frequency acoustic waves in accretion disks with turbulent viscosity

TL;DR

This paper investigates how turbulent viscosity causes instability in high-frequency acoustic waves and various modes within accretion disks, revealing limitations of the thin disk approximation for certain wave numbers.

Contribution

It demonstrates the instability of both low- and high-frequency modes due to turbulent viscosity and assesses the applicability limits of the thin disk model in accretion disk dynamics.

Findings

Turbulent viscosity induces instability in multiple oscillation modes.

High-frequency reflective harmonics are also unstable.

The thin disk model closely approximates 3D models for certain wave numbers.

Abstract

Dynamics of linear perturbations in a differentially rotating accretion disk with non-homogeneous vertical structure is investigated. It has been found that turbulent viscosity results in instability of both pinching oscillations, and bending modes. Not only the low-frequency fundamental modes, but also the high-frequency reflective harmonics appear to be unstable. The question of the limits of applicability of the thin disk model (MTD) is also investigated. The insignificant distinctions in the dispersion properties of MTD and three-dimensional model appear for wave numbers k<(1-3)/h (h is the half-thickness of a disk). In the long-wavelenght limit, the relative difference between eigenfrequencies of the unstable acoustic mode in the 3D-model and the MTD is smaller than 5%.