Thermo-Rotational Instability in Plasma Disks Around Compact Objects

TL;DR

This paper investigates the thermo-rotational instability in plasma disks around compact objects, showing how certain modes can drive the disk toward an adiabatic state and potentially alter its structure.

Contribution

It introduces the concept of thermo-rotational ballooning modes in plasma disks and analyzes their effects on density and temperature profiles and disk evolution.

Findings

Vertical ballooning modes are driven by combined radial and vertical gradients.

These modes tend to push the plasma toward an adiabatic temperature-density profile.

Modes can lead to the formation of plasma rings or different current configurations.

Abstract

Differentially rotating plasma disks, around compact objects, that are imbedded in a ``seed'' magnetic field are shown to develop vertically localized ballooning modes that are driven by the combined radial gradient of the rotation frequency and vertical gradients of the plasma density and temperature. When the electron mean free path is shorter than the disk height and the relevant thermal conductivity can be neglected, the vertical particle flows produced by of these modes have the effect to drive the density and temperature profiles toward the ``adiabatic condition'' where $\eta_{T}\equiv(dlnT/dz)/(dlnn/dz)=2/3$. Here $T$ is the plasma temperature and $n$ the particle density. The faster growth rates correspond to steeper temperature profiles $(\eta_{T}>2/3)$ such as those produced by an internal (e.g., viscous) heating process. In the end, ballooning modes excited for various values of $\eta_{T}$ can lead to the evolution of the disk into a different current carrying configuration such as a sequence of plasma rings.