A Galactic Smash Hit: Galaxy Collision Simulation 

In this visualization of a computer simulation, two spiral galaxies are set on a collision course. As one slices through the other, both are disrupted. The tidal forces of gravity produce long tails of material streaming away from the collision. The central regions relatively quickly fall together and merge.
The visualization is based on a supercomputer simulation, which calculated the motions of 262,144 particles under the forces of gravity and hydrodynamics. The gas particles are shown in blue and the stars in yellow. Each particle is visualized with a size corresponding to its effective size in the calculation. A background field of galaxies was added to provide camera motion clues and astronomical context. The simulation covers roughly 1.5 billion years of the collision.
Visualization: Frank Summers, Space Telescope Science Institute
Simulation: Chris Mihos, Case Western Reserve University, and Lars Hernquist, Harvard University