Galaxies colliding. Supercomputer simulation of two spiral galaxies colliding and merging into a single elliptical galaxy over a period of two billion years. Initially, the galaxies become distorted due to mutual gravitational attraction. As they merge, the interaction causes huge swathes of starbirth in the colliding molecular gas clouds. Eventually, the two large disk-shaped galaxies will settle into a cloud-shaped elliptical galaxy. Most elliptical galaxies observed today formed from collisions that occurred billions of years ago. This will happen within the next few billion years with the Milky Way galaxy and its largest neighbour, the Andromeda Galaxy.