[privong]

Toomre and Toomre, 1972, "Galactic Bridges and Tails". http://adsabs.harvard.edu/abs/1972ApJ...178..623T

This paper addressed the question of how galaxies with bridges and tails were formed. It used a series of simulations with gravitationally interacting point masses and associated test particles to represent the disks of two galaxies. It was one of the first papers to convincingly demonstrate that gravitational tidal interactions can create the narrow "tails" seen extending from some galaxies (others had argued that gravity could not make such narrow tails and argued for magetic fields).

This paper also speculated that gravitational interactions between galaxies could result in an increase in the amount of gas at the centers of galaxies and possibly explain the enhanced rate of star formation and supermassive black hole growth seen in some galaxies galaxies.