This scientific visualization of a computer simulation depicts the inevitable collision between our Milky Way galaxy and the Andromeda galaxy (also known as Messier 31). NASA Hubble Space Telescope observations indicate that the two galaxies, pulled together by their mutual gravity, will crash together in a near-head-on collision about 4 billion years from now. The thin disk shapes of these spiral galaxies are strongly distorted and irrevocably transformed by the encounter. Around 6 billion years from now, the two galaxies will merge to form a single elliptical galaxy.