Dispersion and damping of magnetohydrodynamic modes in radiative plasmas

Abstract

The presented work introduces a theoretical model for radiative magnetohydrodynamics (RMHD) in the equilibrium diffusion limit, focusing on the dynamics of radiation energy. For small amplitude waves, the basic set of dynamic equations is perturbed to derive the dispersion relation for three fundamental modes: fast, intermediate, and slow magnetosonic waves in RMHD plasmas. The study reveals that both fast and slow magnetosonic waves exhibit dispersion and damping in RMHD plasma. It is also revealed that mode conversion between fast and slow RMHD waves occurs at specific values of the wavenumber and propagation angle. The investigation extends to exploring the influence of various parameters characterizing radiative plasma, such as radiation pressure, plasma beta, and radiation diffusivity, on the dispersion and damping of magnetosonic modes (both fast and slow) in RMHD plasma. The findings are elucidated through numerical illustrations. The proposed model finds application in scenarios involving optically thick regions within stars, specifically in their inner atmosphere and interior region. In these regions, the transport of radiation adheres to equilibrium diffusion, and radiation pressure and energy density reach magnitudes comparable to thermal energy and pressure.