The Magnetoviscous-thermal Instability

TL;DR

This paper investigates the stability of magnetized, rotating plasmas with significant viscosity and thermal conductivity, proposing new instabilities that could explain angular momentum and heat transport in radiatively inefficient accretion flows around black holes.

Contribution

It extends previous research by analyzing the stability of dilute, magnetized plasmas considering viscosity and thermal conductivity, identifying new instabilities relevant to accretion physics.

Findings

Identified MHD instabilities that transport angular momentum and thermal energy.

Proposed these instabilities as candidates for accretion processes in RIAFs.

Discussed implications for models and simulations of astrophysical plasmas.

Abstract

Accretion flows onto underluminous black holes, such as Sagittarius A* at the center of our galaxy, are dilute (mildly collisional to highly collisionless), optically thin, and radiatively inefficient. Therefore, the accretion properties of such dilute flows are expected to be modified by their large viscosities and thermal conductivities. Second, turbulence within these systems needs to transport angular momentum as well as thermal energy generated through gravitational infall outwards in order to allow accretion to occur. This is in contrast to classical accretion flows, in which the energy generated through accretion down a gravitational well is locally radiated. In this paper, using an incompressible fluid treatment of an ionized gas, we expand on previous research by considering the stability properties of a magnetized rotating plasma wherein the thermal conductivity and viscosity are not negligible and may be dynamically important. We find a class of MHD instabilities that can transport angular momentum and thermal energy outwards. They are plausible candidates to describe accretion in radiatively inefficient accretion flows (RIAFs). We finish by discussing the implications for analytic models and numerical MHD simulations of mildly dilute or collisionless astrophysical plasmas, and immediate directions for further research.