Antennae Galaxy
The Antennae galaxies take their name from the long antenna-like "arms" extending far out from the nuclei of the two galaxies, as shown to the left. These "tidal tails" were formed during the initial encounter of the galaxies some 200 to 300 million years ago. They give us a preview of what may happen when our Milky Way galaxy collides with the neighboring Andromeda galaxy several billion years in the future.
Credit: B. Whitmore (space Telescope Science Institute) & NASA