Gravitational Instability in a Cylindrical Plasma in a Magnetic Field

概要

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The problem of the stability of an infinitely long cylinder in its own gravitational field in the presence of a magnetic field is investigated by means of the energy principle for a compressible fluid. It is shown that the system may be unstable for sufficiently long wave length perturbations in which the magnetic field lines are interchanged together with the fluid, and as a result of the interchange the gravitational energy of the system is lowered. The cause of the instability is shown to be a convective instability in the gravitational field. In spiral arms of the Galaxy, the growing time of this instability is estimated to be about 10^8 years and the corresponding wave length is 10^3 parsecs for matter density ρ=2×10^<-24>g/cm^3 and magnetic field B=10^<-5> gauss, if the matter is distributed uniformly in the cylinder. The gradient of matter distribution in the radial direction, however, has an effect to supress the instability. It is shown that the present observational distribution of diffused matter is well explained, if we assume that the spiral arms are now in the marginal state against the instability.
理論物理学刊行会の論文
1964-05-25