Spinning around the merging pair of galaxies provides a good view of the collision in the making. The massive dark matter haloes, in which the galaxies are embedded, attract each other through the force of gravity, causing the collision. Hot gas is inside the dark matter haloes, with cooler (green and blue) gas surrounding the pair of haloes. On this large scale, the stellar discs of the galaxies appear tiny.

Sometimes galaxies collide with each other, with the Antennae galaxies a particularly spectacular example. In this example from EAGLE, gas is seen to stream along a tidal arm between the two interacting galaxies. Eventually, gravity will pull these galaxies together forming one galaxy. The Milky Way and Andromeda are on such a collision course.

You can download individual movies by clicking them below.

You can download all of the movies in a zipped folder here.