This image from the Hubble Space Telescope shows the Antennae Galaxies in a state of merger, which began many millions of years ago. Most galaxies merge, rather than collide, but the mergers create havoc with gravity and often cause a major revamping of the structure of both galaxies. Gas and dust within the galaxies are stirred up, and often come together with great ferocity. The end result is usually a much larger individual galaxy, or two highly distorted galaxies with trails of stars in their wakes.

Image Credit: NASA / ESA / STScI / AURA / B. Whitmore

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