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A comment on Mass Extinction and the Structure of the Milky Way (2013). Parent comment

Re:Mass Extinction and the Structure of the Milky Way (2013) by rtkwe on Monday May 08, 2017 @12:51AM (#14289338)
The Spiral arms aren't really cohesive bunches of stars but just bunches of relatively new stars that burn brighter than the older stars outside the spiral arms.

http://www.space.com/24642-spiral-galaxies-milky-way-shape-e...

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Re:Mass Extinction and the Structure of the Milky Way (2013) by Keysh on Monday May 08, 2017 @12:23PM (#14293017)
No, in many spiral galaxies the spiral arms are present in older stars as well; that's why they're considered density waves in the stars. The contrast is stronger for younger stars, but it's there in old stars, too.
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