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Milky Way companion galaxies actually just visiting |
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Written by Derek Kessler on
Tuesday, 18 September 2007
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 Chances are if you've ever taken any sort of astronomy class, you've heard of the Large and Small Magellanic Clouds. We've known about their existance since the time of Magellan (hence, the Magellanic Clounds) - way back in the early 16th century - and all this time we've thought that they were our eternal neighbors, slowly orbiting the Milky Way. Not so, it seems. With just one measurement, the past 500 years of theories on the Magellanic Clouds have been tossed out the hypothetical airlock.
Compared to the large spiral disc of the Milky Way, the Large and Small Magellanic Clouds are fairly small. The Large Magellenic Cloud comes in at about 1/20th the size and resides at a point some 160,000 light-years from Earth, the small is about 1% the size of the Milky Way, and is 200,000 light years away. Both are considered to be irregular galaxies, though it appears that both used to be barred spiral galaxies not unlike our own (just much smaller) that have been severely distorted by the gravitation forces exerted by the 200 billion stars in the Milky Way.
Gurtina Besla of the Harvard-Smithsonian Center for Astrophysics in Massachusetts has been leading a team that was measuring the three-dimensional velocities of both the Magellanic Clouds. They discovered that the miniature galaxies are moving at twice the early predicted velocity, which indicates that they cannot be orbitting the Milky Way. Tidal forces and friction from the Milky Way's massive hydrogen halo have slowed the Magellanic Clouds over time, but it appears that they both are of an origin outside our own local group and are simply sling-shotting around the Milky Way. Just like Kirk.
The Magellanic Clouds are moving at a velocity that would correspond to a parabolic orbit, a trait shared by most comets in our solar system. As is the case, after the Magellanic clouds pass around the Milky Way they will exit our local group on a path that won't bring them back for more than 8 billion years, if they come back at all. For comparison, our Sun is expected to self-destruct via supernova in approximately 4.5 billion years.
Discuss: TrekUnited Forum
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"Take your Vulcan cynicism and bury it with your repressed emotions."
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