Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988a%26a...200..120s&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 200, no. 1-2, July 1988, p. 120-126. Research supported by DFG.
Astronomy and Astrophysics
Astrophysics
2
Disk Galaxies, Galactic Rotation, Perturbation Theory, Rotating Disks, Cosmology, Cylindrical Coordinates, Interstellar Gas, Star Formation
Scientific paper
Global instabilities against axisymmetric polytropic perturbations are investigated for an isothermal self-gravitating thin disk. The idealization of zero thickness is used. Marginally stable perturbations with polytropic exponents 0 < γ < 5/3 are calculated. Besides, the effect of a surrounding envelope on the stability of the disk is considered. The density distribution of the envelope is that of the isothermal gas sphere. The stability depends on the ratio of the rotational velocity to the sound velocity, the value of γ, and the ratio of the mass of the envelope to that of the disk. Ring-mode instabilities occur for disks with large rotational velocities, collapse instabilities can occur at small velocities. The stabilizing effect of the envelope is considerable. In the case of an isolated disk for γ > 1.34 all equilibrium states are stable with respect to collapse. For γ < 0.75 there are no stable isolated disks.
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