Figure: Early N-body simulation for the Mice Galaxies

N-body simulations by A. Toomre and J. Toomre, Astrophysical Journal, 178, 623-666 (1972).
(Copyright: Astrophysical Journal)

This paper was the first to convincingly argue (and show) that the bridges and tails seen in some multiple galaxies are just tidal relics of close encounters.

A pdf version of Toomre and Toomre's paper is available here.