Magellanic Stream mystery solved by Hubble telescope
16 Sep 2013 by Evoluted New Media
A 40-year old mystery has been solved by astronomers using NASA’s Hubble Space Telescope. They have uncovered the origin of the Magellanic Stream, a long ribbon of gas stretching nearly halfway around our Milky Way galaxy.
Two dwarf galaxies orbiting the Milky Way – the Large and Small Magellanic Clouds – are at the head of the Magellanic Stream. Since the stream was discovered in 1970s, astronomers have wondered whether the gas comes from one or both of the satellite galaxies.
Researchers have now been able to determine the source of the gas filament using Hubble’s Cosmic Origins Spectrograph to measure the amount of heavy elements at six locations along the stream. The observations reveal most of the gas was stripped from the Small Magellanic Cloud about 2 billion years ago, and a second region of the stream originated more recently from the Large Magellanic Cloud.
Andrew J. Fox, from the Space Telescope Science Institute in Baltimore, who led the research, said: “We’re finding consistent amounts of heavy elements in the stream until we get very close to the Magellanic Clouds, and then the heavy element levels go up. This inner region is very similar in composition to the Large Magellanic Cloud, suggesting it was ripped out of the galaxy more recently.”
The Magellanic Clouds have a special feature compared to other satellite galaxies of the Milky Way – they have been able to retain their gas and are still forming stars. As they approach the Milky Way, they are influenced by its gravity and encounter its halo of hot gas. It is this process, together with the gravitational tug-of-war between the two galaxies that leads to the production of a stream.
The stream may ultimately rain down onto the Milky Way’s disk fuelling the birth of new stars – infusion of fresh gas is part of a process that triggers star formation. Researchers wanted to know the true origin of the wayward gas in order to comprehensively understand how galaxies make new stars.
“We want to understand how galaxies like the Milky Way strip the gas from small galaxies that fall into them and then use it to form new stars. This seems like it’s an episodic process. It’s not a smooth process where a slow stream of gas comes in continuously. Instead, once in a while a large gas cloud falls in. We’ve shown which of them is producing the gas that ultimately will fall into the Milky Way,” Fox explained.
The team’s results appear in The Astrophysical Journal.
