On gravitational instability of the interstellar gas |
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| Authors: | Bruno Bertotti Alfonso Cavaliere |
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| Institution: | (1) Istituto di Fisica dell'Università, Messina, Italy;(2) Laboratorio Gas Ionizzati, Frascati (Roma), Italy;(3) Present address: European Space Research Institute, Frascati (Rome) |
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| Abstract: | In the galaxy, Jeans' critical length for the interstellar gas is appreciably smaller than the critical length for the stars, a necessary condition for the gravitational instability of the former to have a local character. An accurate discussion of the orders of magnitude involved leads to the establishment of a well defined limiting procedure and to simplified equations in which the effect of stars occurs only through the equilibrium, but disappears from the perturbations. The equations are spatially local, but their coefficients are time-dependent, in that they describe the evolution of a small wave packet dragged along by the supersonic gas motion. They have been solved in several interesting cases by the introduction of an effective, time-dependent wave vector, which describes the deformation of a wave profile due to the velocity gradients. The ordinary Jeans' instability is recovered only when the velocity gradient is a skew tensor; otherwise we find a stabilizing effect in accelerated and sheared flows, a destabilizing effect in a decelerated flow. Possible connections of this model with the observed turbulent structure of the interstellar gas are discussed. |
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