August 8, 2013
Hubble Discovers Source Of Magellanic Stream
John P. Millis, PhD for redOrbit.com - Your Universe Online
Stretching almost halfway around the Milky Way galaxy, the Magellanic Stream is a ribbon of gas that has puzzled astronomers for decades. Now, using data from the Hubble Space Telescope (HST), astronomers now believe that they have nailed down its source.Visible from the southern hemisphere, the dwarf galaxies known as the large and small Magellanic Clouds - the LMC and SMC, respectively - are two of our nearest galactic neighbors. They may have originally been small spiral galaxies, but the gravitational pull of the much larger Milky Way has distorted their shape and caused them to look more irregular.
And this latest study from the HST indicates that it may be gas from these dwarf galaxies that is responsible for generating the Magellanic Stream. Researchers believe that most of the gas was stripped off of the SMC, and recently, some of the gas has come from the larger of the two dwarf galaxies. This actually wasn't much of a surprise to researchers, as they had wondered whether the origin could be traced back to the Magellanic clouds since the discovery of the ribbon of gas back in the 1970s.
The team was able to make the definitive connection between the stream of gas and the clouds by analyzing the relative gas abundances in the different systems. They found that the levels in the ribbon were consistent with that of the SMC some two billion years in the past, coinciding with when the stream is thought to have formed.
There was something that the team did not expect, however: there were much higher levels of sulphur in a region close to the Magellanic Clouds. "We're finding a consistent amount of heavy elements in the stream until we get very close to the Magellanic Clouds, and then the heavy element levels go up," said Andrew Fox in statement to the ESA. Fox is a staff member supported by ESA at the Space Telescope Science Institute, USA and lead author of one of the two studies on the region. "This inner region is very similar in composition to the Large Magellanic Cloud, suggesting it was ripped out of that galaxy more recently."
This was surprising because scientists had long believed that the sole source of the stream was from the SMC, giving it its weaker gravitational field. "As Earth's atmosphere absorbs ultraviolet light, it's hard to measure the amounts of these elements accurately, as you need to look in the ultraviolet part of the spectrum to see them," says Philipp Richter of the University of Potsdam in Germany, lead author on the second of the two papers. "So you have to go to space. Only Hubble is capable of taking measurements like these."
"Exploring the origin of such a large stream of gas so close to the Milky Way is important," adds Fox. "We now know which of our famous neighbors, the Magellanic Clouds, created this gas ribbon, which may eventually fall onto our own galaxy and spark new star formation. It's an important step forward in figuring out how galaxies obtain gas and form new stars."