Effect of temperature gradient on the wave propagation in a self-gravitating medium and its role in the central region of our Galaxy

Abstract

The wave propagation in a finitely conducting, self-gravitating, non-relativistic hydromagnetic medium with temperature gradient and a heat-energy transport into it has been considered. Firstly, a General Dispersion Relation (G.D.R.) has been derived. The interest has been kept limited for the study of one dimensional wave propagation in a typical medium where magnetic field and it's gradient, density gradient, temperature gradient are all along the direction of wave propagation. The D.R. of such a medium follows from G.D.R. In particular, the effect of temperature gradient on the wave propagation has been studied. Analytical expressions for the wave parameters have been derived under different conditions. It has been found that the longitudinal waves could be sufficiently energetic for being unstable by the temperature gradient. Further, the modified Jeans' criterion (depending on temperature gradient), a criterion important for stability, has also been obtained. On assuming the gas medium in the central region (≲ 10 pc) of our Galaxy to behave like hydromagnetic fluid, and the direction of wave propagation (z-direction) as the direction perpendicular to the Galactic plane, few numerical estimations for the wave parameters (like wave lengths, phase velocity, etc.) have been made (as application of the above theoretical discussions). It has been found that the phase velocity of longitudinal waves at 1 pc level is at least 170 kms−1 while at the 10 pc level the longitudinal waves of length less than a parsec may propagate smoothly through the medium. It has been suggested that (i) in the central region (≲ 10 pc) of our Galaxy the temperature gradient could be one of the major causes of the mass-outflow along the direction perpendicular to the Galactic plane (ii) outside the central region (≲ 10 pc) of our Galaxy, there may be long term consequences of such mass-outflow like Halo formation.