Published in "The Evolution of Galaxies and Stellar Populations", eds. Beatrice M. Tinsley and Richard B. Larson, Yale University Observatory, 1977.
Abstract. As I hardly need to remind you, it has dawned rather widely in the last few years that the old notion of dynamical friction - tucked away in several 1943-vintage appendices to Chandrasekhar's (1942) book, and long appreciated mostly just by stellar dynamicists impressed by the rapid sinking of heavy masses in N-body simulations of star clusters - applies even to galaxies in a variety of settings. In his review, Ostriker has already stressed one such setting, the great clusters like Coma. Here I will focus on just the opposite extreme; some strange goings-on in mere pairs. Of course, neither of us would dispute that many modest groups and loose clusters of galaxies exist also, but for the moment it seems best to ignore them.
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