Nasa has solved a gigantic galactic mystery - literally - by finding the elusive source of the Magellanic Stream.
The Magellanic Stream is a long ribbon of gas which stretches nearly halfway around the galaxy, from our perspective. It's been known about for more than 40 years, but its source has remained hidden from our site.
But now a team of astronomers led by Andrew J. Fox of the Space Telescope Science Institute in Baltimore think they have the answer.
They used data from Hubble's Cosmic Origins Spectrograph to measure the amount of heavy elements, such as oxygen and sulfur, at six locations on the stream.
What they found was a low amount of oxygen and sulfur, matching the levels in the Small Magellanic Cloud, a dwarf galaxy which orbits the Milky Way at the head of the stream.
As a result, they now think the ribbon was formed when gas was stripped from the Small cloud about 2 billion years ago.