Figure 13-44 Interacting and Colliding Galaxies (a) Pairs of colliding galaxies often exhibit long “antennae” of stars ejected by the collision. This particular system is known as NGC 4676 or “the Mice” (because of its tails of stars and gas). It is 300 million light-years from Earth in the constellation Coma Berenices. The collision has stimulated a firestorm of new star formation, as can be seen in the bright blue regions. Mass can also be seen flowing between the two galaxies, which will eventually merge. (b) These two galaxies, NGC 2207 (right) and IC 2163, are orbiting and tidally distorting each other. Their most recent close encounter occurred 40 million years ago when the two were perpendicular to each other and about 1 galactic diameter apart. Computer simulations indicate that they should eventually coalesce.