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Tuesday, October 11, 2005

How Big is a Galaxy?

There is more than one discipline with unsettled theoretical models. Those darn data can be so inconvenient:

Milky Way: Larger, Weirder?, Discover: Galaxies are large, but many of them-including the Milky Way-are much larger than suspected. Astronomers at the Keck observatory in Hawaii have found that the Andromeda galaxy-our closest galactic neighbor, 2.2 million light-years away and a familiar sight in the evening sky-is three times bigger than previously thought. Spectrographic analysis shows that 3,000 stars, once believed to be separate from Andromeda, move in lockstep with that galaxy's rotation, as part of its outer disk. "It was completely unexpected says Caltech astrophysicist Scott Chapman... In a related finding, new images from the Gemini South telescope in Chile exposed another giant disk around NGC 300, a far less massive galaxy that resembles our own but is 6 million light-years away. Using Gemini's high-end optics, Joss Bland-Hawthorn of the Anglo-Australian Observatory and astronomer Ken Freeman of the Australian National University counted the brightest stars on the galaxy's fringes. The census shows that, like Andromeda, NGC 300 boasts a broad disk-in this case one that effectively doubles the galaxy's size. The new measurements mean that astronomers must rethink how galaxies are formed. "The one thing that is clear is that all the models of galaxy formation do not predict such large spinning disks," says Chapman. These models typically assume that galaxies were created by gases clumped together by gravity. Since the gases thin out away from the core, star concentration should ease rapidly, and galaxies should exhibit sharp edges. But the stars appear to be obeying unknown rules, tapering off evenly...

[I can't resist this stuff. Apologies there isn't a link - it was typed from the magazine.]

    Posted by on Tuesday, October 11, 2005 at 12:06 AM in Science | Permalink  TrackBack (0)  Comments (6)

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