Effects of cosmic radiation pressure on the gravitational instability of rotating plasmas

Abstract

This paper uses hydromagnetic fluid descriptions to study the effects of cosmic ray (CR) pressure and CR diffusion on the gravitational instability of uniformly rotating plasmas. The effects of cosmic radiation pressure have been incorporated through the CR pressure gradient terms in the momentum transfer equation of plasmas and the energy equation of CRs. In the fluid description, the CR fluid interacts with the gravitating, uniformly rotating and infinitely conducting plasmas by modifying the instability properties of the system. The dispersion relation of the gravitational instability has been derived with the help of linearized perturbation equations and using the normal mode analysis. It is found that the classical gravitational instability criterion remains unaffected due to the presence of rotation and CRs. But, it gets modified by the CR pressure-driven acoustic mode when CR diffusion is absent in the system. From the curves, we found that CR pressure stabilizes, whereas CR diffusion destabilizes the growth rate of the gravitational instability. The results are helpful to understand the role of cosmic radiation pressure and CR diffusion on the gravitational instability of plasma present in rotating accretion disks.