The formation of elliptical galaxies by tidal interactions

Abstract

The suggestion is examined that elliptical galaxies result from the collisional heating of initially flat galaxies. A Maclaurin spheroid model is adopted for a rotating galaxy, and the rate at which galaxies are thickened by tidal encounters (including interpenetrations) in the isothermal cores of rich clusters of galaxies is investigated. The heating rate of galaxies in the cores of the densest clusters (e.g., Coma) is sufficiently high to explain the observation that elliptical galaxies are concentrated in such regions. Collisional heating also places an upper limit to the typical masses of black holes assumed to be isothermally distributed and sufficiently numerous to account for the nonluminous ('missing') mass of the Coma cluster.