Content area
Abstract
In many astrophysical plasmas, the mean free path is large, and thermal conduction occurs primarily along magnetic field lines. As a result, the usual convective stability criterion is modified from a condition on entropy to a condition on temperature. For small magnetic fields or large wavelengths, instability occurs in any atmosphere where the temperature and pressure gradients point in the same direction. I refer to the resulting convective instability as the magnetothermal instability (MTI). In this thesis I present two- and three-dimensional simulations of the MTI using new computational methods that combine magnetohydrodynamics (MHD) with anisotropic thermal conduction along magnetic field lines. I demonstrate tests of both the MHD and conduction algorithms and show that they parallelize well. I show excellent agreement between linear theory and computational measurements of the growth rates. In the nonlinear regime, I find that this instability can dramatically rearrange the thermal structure of an atmosphere and drive a magnetic dynamo. I then study the MTI in the intracluster medium (ICM) of clusters of galaxies. Clusters of galaxies are the largest gravitationally bound objects in the universe, yet the fundamental physics of the structure, heating, and cooling of the ICM are poorly understood. I show that the ICM is unstable to the magnetothermal instability. As a result of the MTI, I find that the temperature profile of the ICM can be substantially modified on timescales of several billion years while the magnetic field is amplified by dynamo action. I also find that the saturated state of the magnetic field has a highly radial structure. Finally, I explore some of the potential observational consequences of the MTI in galaxy clusters.
