On gas dynamical models of galaxies

This paper discussed the range of applicability of the gas dynamical equations used in gas dynamical models. It is pointed out that (1), when dealing with gravitational collapse, the law of mass conservation and the equation of continuity are inapplicable if the reaction energies are large. (2) The presence of turbulence only affects the basic-state motion. If the basic-state motion is given and if we neglect higher-order small quantities and if we make certain simplifying assumptions, then the equations for small perturbations are of the same form as in the absence of turbulence. The equations used by C.C. Lin and his coworkers are precisely equations for small perturbations, hence Lin's theory still holds even if there is turbulence. If we wish to go to the next approximation, then we must, in general, take account of turbulence.