The Antennae Galaxies in Collision . ... When two galaxies collide , the stars that compose them usually do not. That's because galaxies are mostly empty space and, however bright, stars only take up only a small amount of that space. During the slow, hundred million year collision , one galaxy can still rip the other apart gravitationally, and dust and gas common to both galaxies does collide . ... NASA Web Site Statements, Warnings, and Disclaimers . NASA Official: Jay Norris. ...