Princeton University Astroplasmas Seminar - TIME CHANGED!

ABSTRACT: In weakly-collisional plasmas such as the intracluster medium (ICM), heat and momentum transport become anisotropic with respect to the local magnetic field direction. Anisotropic heat conduction causes the slow magnetosonic wave to become buoyantly unstable to the magnetothermal instability (MTI) when the temperature increases in the direction of gravity and to the heat-flux--driven buoyancy instability (HBI) when the temperature decreases in the direction of gravity. The local changes in magnetic field strength that attend these instabilities cause pressure anisotropic that viscously damp motions parallel to the magnetic field. In this talk, I will discuss two important effects of pressure anisotropy on the dynamical and thermal stability of the ICM. First, by stifling the convergence/divergence of magnetic field lines, pressure anisotropy significantly affects how the ICM interacts with the temperature gradient. Instabilities which depend upon convergence/divergence of magnetic field lines to generate unstable buoyant motions (the HBI) are suppressed over much of the wavenumber space, whereas those which are otherwise impeded by field-line convergence/divergence (the MTI) are strengthened. Second, because the viscous heating of the ICM is regulated by the pressure anisotropy -- which itself is nonlinearly regulated by the plasma beta parameter via rapidly-growing micro scale instabilities -- pressure anisotropy may play a crucial role in mitigating cooling flow and preventing cluster core collapse. I will discuss the physical interpretation of these effects in detail, placing them within the larger context of formulating a pragmatic analytical and numerical framework for modeling astrophysical multi-scale plasma dynamics.