Crash of the Titans: Milky Way & Andromeda Collision [Ultra HD] 

In about 4 billion years, the Milky Way and Andromeda galaxies will collide.
The three largest galaxies in our Local Group of Galaxies are our Milky Way along with the Andromeda (also known as Messier 31) and Triangulum (also known as Messier 33) galaxies. This scientific visualization of a computer simulation depicts their joint evolution over the next several billion years and features the inevitable massive collision between the Milky Way and Andromeda. Hubble Space Telescope observations indicate that the two galaxies, pulled together by their mutual gravity, will crash together in a 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. The Triangulum galaxy continues to orbit the merged pair through the end of this computer simulation, though other computer models show it becoming part of the collision.
The visualization covers 8.2 billion years into the future at 105 million years per second. Colors are representative: light blue for spiral galaxies (considered "blue" in astronomy parlance because of their active star formation) and orange-yellow for elliptical galaxies (called "red" by astronomers for their old stellar populations). A random background field of galaxies has been added to the simulation in order to indicate the camera motion through the simulation volume.
This visualization depicts the same simulation as the "Future Galaxy Merger" visualization, but includes the Triangulum galaxy and utilizes a more cinematic camera choreography.
Visualization: Frank Summers (STScI)
Simulation: Gurtina Besla (Columbia University) and Roeland van der Marel (STScI)