How monster galaxies feed off of their neighbors

In very large, ancient galaxies, usually more than ten billion light-years away from us, many stars behave differently than in the Milky Way, where the large majority of stars obediently follow the motion of arms rotating about the center of the galaxy. Why is that? It seems galaxies have something in common with people: when theres too much substance around their mid-sections, its usually a result of too much eating. Giant galaxies have swallowed up too many of their neighbors, one after the...