MessageToEagle.com - Astronomers using the NASA/ESA Hubble Space Telescope have solved the 40-year-old mystery
of the origin of the Magellanic Stream, a long ribbon of gas stretching nearly halfway around the Milky Way.
New Hubble observations reveal that most of this stream was stripped from the Small Magellanic Cloud some two billion
years ago, with a smaller portion originating more recently from its larger neighbor.
The Magellanic Clouds, two dwarf galaxies orbiting our galaxy, are at the head of a huge gaseous filament known as
the Magellanic Stream. Since the Stream's discovery in the early 1970s, astronomers have wondered whether this gas
comes from one or both of the satellite galaxies.
Click on image to enlarge
hese images show wide and close-up views of a long ribbon of gas called the Magellanic Stream, which stretches nearly halfway around the Milky Way. In the combined radio and visible-light image at the top, the gaseous stream is shown in pink. The radio observations from the Leiden/Argentine/Bonn (LAB) Survey have been combined with the Mellinger All-Sky Panorama in visible light. The Milky Way is the light blue band in the centre of the image. The brown clumps are interstellar dust clouds in our galaxy. The Magellanic Clouds, satellite galaxies of the Milky Way, are the white regions at the bottom right. (Credit: Credit for the radio/visible light image: David L. Nidever, et al., NRAO/AUI/NSF
and Mellinger, LAB Survey, Parkes Observatory, Westerbork Observatory, and Arecibo Observatory. Credit for the radio image: LAB Survey.
Now, new Hubble observations show that most of the gas was stripped from the Small Magellanic Cloud about two
billion years ago - but surprisingly, a second region of the stream was formed more recently from the Large
A team of astronomers determined the source of the gas filament by using Hubble's Cosmic Origins Spectrograph (COS),
along with observations from ESO's Very Large Telescope, to measure the abundances of heavy elements, such as oxygen
and sulphur, at six locations along the Magellanic Stream.
COS detected these elements from the way they absorb the ultraviolet light released by faraway quasars - the brilliant
cores of active galaxies - as it passes through the foreground Stream.
The team found low abundances of oxygen and sulphur along most of the stream, matching the levels in the Small
Magellanic Cloud about two billion years ago, when the gaseous ribbon was thought to have been formed.
"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," says Andrew Fox, a staff member supported by ESA at the Space Telescope Science Institute, USA, and lead author of one of two new papers reporting these results.
"This inner region is very similar in composition to the Large Magellanic Cloud, suggesting it was ripped out of that galaxy more recently."
Click on image to enlarge
All-sky view of the Magellanic Stream (radio/visible-light)
This image shows a long ribbon of gas called the Magellanic Stream, which stretches nearly halfway around the Milky Way.
In this combined radio and visible-light image, the gaseous stream is shown in pink. The radio observations are taken from the Leiden/Argentine/Bonn (LAB) Survey. The Milky Way is the light blue band in the centre of the image. The brown clumps are interstellar dust clouds in our galaxy. The Magellanic Clouds, satellite galaxies of the Milky Way, are the white regions at the bottom right.
Credit: David L. Nidever, et al., NRAO/AUI/NSF and Mellinger, Leiden/Argentine/Bonn Survey, Parkes Observatory, Westerbork
Observatory, and Arecibo Observatory.
In a surprising twist, the team discovered a much higher level of sulphur in a region closer to the Magellanic Clouds.
This discovery was unexpected; computer models of the Stream predicted that the gas came entirely out of the Small Magellanic Cloud, which has a weaker gravitational pull than its more massive cousin.
"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, Germany, and 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."
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