On the Gravitational Instability of Some Magneto-Hydrodynamical Systems of Astrophysical Interest. Part III.
Abstract
Chapter 9. Magneto-hydrostatic equilibrium of an infinite isothermal cylinder gas is considered. Two cases are distinguished: a - the lines of forces of the magnetic field are concentric circles around the symmetry axis of the system, lying in planes perpendicular thereto; b - the lines of forces are parallel to the axis of the cylinder. The magnetic field intensity is assumed proportional to the square root of the gas density. The latter is computed (9.23) as a function of the distance from the axis of symmetry. Chapter 10. Criteria for the critical length of a perturbation, for both configurations of the magnetic field of Chapter 9, are derived. In the case a, the critical length to the perturbation increases with the magnetic field intensity (10.31). If the lines of magnetic forces are parallel to the axis of the cylinder, the critical length of the perturbation decreases with the rise in magnetic field intensity (10.63). The stability of a plane-parallelly stratified, self-gravitating medium when the perturbation propagates along the magnetic field is examined. The critical length of the perturbation decreases with the rise in magnetic field intensity (10.101). Chapter 11. The effect of stars present in a gaseous spiral arm of the Galaxy on the criterion for critical length of a perturbation imposed on that arm is considered. A criterion (11.17) for the critical length of the perturbation is derived, pointing to a stabilizing effect of the stars. Chapter 12. The gravitational stability of the Perseus' arm is considered. The latter is found to be gravitationally instable; the formation therein of gas condensations about 2 kpc in size is predicted. It seems plausible that the condensations observed in the 21 cm line in this arm are due to its gravitational instability.
- Publication:
-
Acta Astronomica
- Pub Date:
- 1963
- Bibcode:
- 1963AcA....13...30S
- Keywords:
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- STABILITY;
- THEORY;
- MAGNETIC FIELDS