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f10_nov30 - The rotation curve of the Galaxy tells us the...

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Ast 307 - Nov. 30, 2010 The Past, Present, & Future of the Universe The rotation curve of the Galaxy tells us the distribution of mass Most spiral galaxies have flat rotation curves, indicating that there are large amounts of dark matter in their outer regions. Dark Matter in Other Spiral Galaxies Most elliptical galaxies don’t rotate, but the absorption lines (coming from the stars in them) are broadened by the motions of the stars, and one can calculate the mass of the galaxy from this broadening. Result: These galaxies also contain dark matter. Dark Matter in Elliptical Galaxies
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We can measure the velocities of galaxies within a cluster from their Doppler shifts… The mass found this way is ! 50 times the mass seen in stars Dark Matter in Galaxy Clusters: I. Motions of individual galaxies Some galaxy clusters also contain large amounts of hot, X-ray emitting gas. The gas temperature (average particle velocity) tells us the total mass: 2% stars 13% hot gas 85% dark matter Dark Matter in Galaxy Clusters: II. Retention of Hot Gas Gravitational lensing, the bending of light rays by gravity, provides another way to measure the cluster’s mass Dark Matter in Galaxy Clusters: III. Gravitational Lensing Dark Matter in Galaxy Clusters
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Resolution of Olbers’ Paradox The Cosmic Microwave Background: The “3-degree Background Radiation” We see a nearly uniform glow, all over the sky, from the early hot universe. This thermal radiation has been so
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