Phase Segregation in a Two-Phase Self-gravitating Gas Mixture

Details Phase Segregation in a Two-Phase Self-gravitating Gas Mixture Phase Segregation in a Two-Phase Self-gravitating Gas Mixture

Jul 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...501..666k&link_type=abstract

Astrophysical Journal v.501, p.666

Astronomy and Astrophysics

Astronomy

3

Galaxy: Evolution, Galaxy: Formation, Gravitation, Hydrodynamics, Ism: Clouds, Stars: Formation, Waves

Scientific paper

We discuss the stability of a self-gravitating two-phase gas mixture by linear analysis. The mixture is composed of diffuse phase and immersed dense clouds in pressure equilibrium. Earlier we have shown that in a two-phase self-gravitating mixture, two fundamental wave modes are relevant: (1) the gravitationally modified sound mode with the intrinsic Jeans length lambda J1 and (2) the modified void (or pattern formation) mode with the Jeans length lambda J2. In this paper, we describe the effect of stabilization of perturbations in a two-phase self-gravitating mixture: when the diffuse phase dominates in volume (the volume filling factor alpha ~= 1), the pattern formation mode is gravitationally unstable for lambda > lambda cr, while the fast acoustic mode remains gravitationally stable for arbitrary lambda ; when the dense phase dominates ( alpha << 1), the slow acoustic mode is gravitationally unstable, while the fast pattern formation mode is stable. The stabilization is caused by displacement of the light component by agglomerating dense clouds: gravitationally unstable dense phase displaces light diffuse phase and thus excites in it wave motions. We argue that gravitational instability of the pattern formation mode results in the segregation of phases. The critical length lambda cr depends on parameters of phases and their volume filling factors and can vary from 8 pc for molecular clouds to 0.1-0.5 kpc for spiral galaxies and protogalaxies. We briefly discuss possible consequences of the stabilization effect for the two-component model of protogalaxies.

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