Parker‐Jeans Instability of Gaseous Disks Including the Effect of Cosmic Rays

We use linear analysis to examine the effect of cosmic rays (CRs) on theParker-Jeans instability of magnetized self-gravitating gaseous disks. We adopta slab equilibrium model in which the gravity (including self-gravity) isperpendicular to the mid-plane, the magnetic field lies along the slab. CR isdescribed as a fluid and only along magnetic field lines diffusion isconsidered. The linearised equations are solved numerically. The system issusceptible to Parker-Jeans instability. In general the system is less unstablewhen the CR diffusion coefficient is smaller (i.e., the coupling between theCRs and plasma is stronger). The system is also less unstable if CR pressure islarger. This is a reminiscence of the fact that Jeans instability and Parkerinstability are less unstable when the gas pressure is larger (or temperatureis higher). Moreover, for large CR diffusion coefficient (or small CRpressure), perturbations parallel to the magnetic field are more unstable thanthose perpendicular to it. The other governing factor on the growth rate of theperturbations in different directions is the thickness of the disk or thestrength of the external pressure on the disk. In fact, this is the determiningfactor in some parameter regimes.Comment: 19pages, 14figures submitted to Ap