A dynamical interpretation of the Hubble sequence of galaxies.

A theory of galactic evolution has been proposed by Brosche (1970), according to which a galaxy is driven by energy loss due to collisions among galactic gas clouds through virial equilibrium states from an initial spherical shape to a contracted elongated shape. The total angular momentum is assumed to determine the galaxy type in the Hubble sequence and to influence the time of contraction from the initial spherical to the final flat configuration. In the present paper, Brosche's scheme is modified by assuming as models the rotating polytropes of Chandrasekhar and Lebovitz with variable density from center to border. Centrifugal shedding of matter is attained at the equator of the contracting ellipsoid for a configuration with an axial ratio different from zero. A flat disk is formed surrounding the internal bulge, with a decreasing overall eccentricity. The rotation curve assumes, as a result, an aspect qualitatively similar to the one observed for spiral galaxies. Star formation feedback has been also considered. Varying the angular momentum different galaxy types of the Hubble sequence could be obtained.