The Mice colliding galaxies, optical image taken by the Hubble Space Telescope's new Advanced Camera for Surveys (ACS) on April 7th 2002. These galaxies (NGC 4676) were once spiral in shape, but the gravitational interaction has thrown off long tails of stars and distorted their nuclei (yellow). It has also caused a burst of star formation activity, as seen by the abundance of hot young blue stars. The galaxies will combine to form one large elliptical galaxy in several million years time. The Mice are around 300 million light years from Earth in the constellation Coma Berenices.