|Annu. Rev. Astron. Astrophys. 1984. 22:
Copyright © 1984 by . All rights reserved
Some of the most exotic specimens of neutral hydrogen distributions are found where galaxies seem to come together. In fact, neutral hydrogen proves to be an even better tracer of tidal disruption than does starlight. In this section, we examine the occurrence of neutral hydrogen streams, the interactive nature of galaxies in groups, and the ultimate fate of the gas, stars, and galaxies that partake in such encounters.