Abstract:
The results of a linear stability analysis of gaseous disk, in which
heating and radiative cooling is dynamically important, we are
presented. It is shown that cooling gives weak damping of acoustical
modes and make more unstable gravity modes. So, the entropical-gravity
mode is unstable for any wavelength and the local criterion of
gravitational stability is absent. These effects may to influence on
the mechanism of observational structure of gaseous disk in galaxies
forming.
The physical cause of instability is phase shift between disturbances
of internal energy and pressure on the one hand and disturbances of
density on other hand, which uniquely determines by dispersion law.
For acoustic modes all disturbances are in phase — increase of
density leads to increase of internal energy; the wave behaves in the
usual way. For the entropy modes disturbances of density are not in
phase with disturbances of pressure and internal energy. So, local
increase of density leads to decrease of pressure and internal energy.
This is energetically favorable in accordance with the Le Chatelier
— Brown principle and increases in time.
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