A thin trail of neutral hydrogen which stretches in a great circle around the sky for about 150° from the Magellanic Clouds, passing near the south galactic pole. It is thought to be debris pulled from the Small Magellanic Cloud in a close encounter with the Large Magellanic Cloud about 2 billion years ago.

http://hubblesite.org/newscenter/archive/releases/2013/27/ Pictures of the Magellanic Stream from the Hubble Space Telescope.