Parker-Jeans instability of gaseous disks including the effect of cosmic rays

Takuhito Kuwabara, Chung Ming Ko

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18 Scopus citations


We use linear analysis to examine the effect of cosmic rays (CRs) on the Parker-Jeans instability of magnetized self-gravitating gaseous disks. We adopt a slab equilibrium model in which the gravity (including self-gravity) is perpendicular to the midplane and the magnetic field lies along the slab. CRs are described as a fluid, and diffusion is considered only along magnetic field lines. The linearized equations are solved numerically. The system is susceptible to Parker-Jeans instability. In general, the system is less unstable when the CR diffusion coefficient is smaller (i.e., the coupling between the CRs and plasma is stronger). The system is also less unstable if the CR pressure is larger. This is reminiscent of the fact that Jeans instability and Parker instability are less unstable when the gas pressure is larger (or temperature is higher). Moreover, for a large CR diffusion coefficient (or a small CR pressure), perturbations parallel to the magnetic field are more unstable than those perpendicular to it. The other governing factor on the growth rate of the perturbations in different directions is the thickness of the disk or the strength of the external pressure on the disk. In fact, this is the determining factor in some parameter regimes.

Original languageEnglish
Pages (from-to)290-302
Number of pages13
JournalAstrophysical Journal
Issue number1 I
StatePublished - 1 Jan 2006


  • Cosmic rays
  • Instabilities
  • ISM: magnetic fields
  • MHD


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