NASA Hubble Space Telescope Discovers Origin of Magellanic Stream

NASA's Hubble Space Telescope has made a surprising discovery. It's found the origin of the Magellanic Stream, a long ribbon of gas stretching nearly halfway around the Milky Way galaxy. The findings solve a 40-year mystery that continually baffled scientists.

The Large and Small Magellanic Clouds are active dwarf galaxies orbiting the Milky Way at the head of this gaseous stream. Scientists have long wondered whether the gas from the Megellanic Stream comes from these galaxies. Now, the new observations may have shown researchers the answer.

In order to get a better sense of where exactly this stream of gas was coming from, the researchers used Hubble's Cosmic Origins Spectrograph (COS). This allowed them to measure the amount of heavy elements, such as oxygen and sulfur, at six locations along the Magellanic Stream. More specifically, COS observed the brilliant cores of active galaxies whose emitted light passed through the stream and detected these elements from the way they absorb ultraviolet light.

So what did they find? The scientists discovered a low amount of oxygen and sulfur along most of the stream. These levels matched ones found in the Small Magellanic Cloud about 2 billion years ago, which is the time period when the stream was thought to have formed. The astronomers also found a much higher level of sulfur closer to the Magellanic Clouds, which seemed to indicate that the more recent material was ripped from the Large Magellanic Cloud.

The findings are unexpected. Computer models actually predicted that the gas came entirely out of the Small Magellanic Cloud, which has less gravity that its massive cousin. The new observations, though, indicate otherwise.

"What's interesting is that all of the other nearby satellite galaxies of the Milky Way have lose their gas," said Andrew J. Fox, one of the researchers, in a news release. "The Magellanic Clouds have been able to retain their gas and are still forming stars because they're more massive than the other satellites. However, as they're now approaching the Milky Way, they're feeling its gravity more and also encountering its halo of hot gas, which puts pressure on them. That process, together with the gravitational tug-of-war between the Magellanic Clouds, leads to the production of the stream."

The findings reveal not only the origins of this stream, though. They also show what may happen in the future. The gaseous stream may eventually rain down on the Milky Way's disk, fueling the birth of new stars.

The findings are published here and here in The Astrophysical Journal.