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Lecture 25

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Laura Parker

Lecture 25Friday November 11 20111230 PMThe dark universeQuarter of the mass of the universeMost of the universe is made up of something we dont know dark matterEvidence for dark matterMotions of galaxies in clustersSpiral galaxy rotation curvesGravitational lensingEarly evidence for dark matter1933 Fritz Zwicky made the first estimates of the masses of clusters of galaxieswo extra mass the galaxies would have velocities too high to stay in clustersHe measured the velocities of the coma cluster and their escape velocities were at the speed they should beable to escape so there must be some kind of mass that we dont see holding the galaxies in the clusterWhat did Zwicky doFound the existence of dark matterHe measured the speeds of galaxies then through the speeds found the mass of the whole galaxy then compared that mass to the visible luminous mass of the galaxy which was much smaller than the whole galaxy clusters mass Dark matterWhat did Zwicky findtotal massmass in starsgasfew hundredThere is some mass that we cannot see in these clustersNext slideSpeed of rotation can tell us the mass of the objectsSpeed of rotation can be measured using spectrum linesYour only sensiti
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