ASTRON 2B03 Lecture Notes - Lecture 15: Orbital Speed, Weak Gravitational Lensing, Measure R
10 Apr 2018
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Astronomy 2b03 lecture lomoar cpsd| 2151316 lomoar cpsd| 2151316. In 1933, fritz zwicky made the rst estimates of the masses of clusters of galaxies. Without extra mass the galaxies would have velocities too high to stay in the cluster! Total mass/mass in stars+gas = ~a few hundred (estimate was a little high but good idea) We repeat zwicky(cid:1932)s measurement and nd the exact ratio of dark matter to luminous matter andromeda galaxy m31 closest big galaxy to the milky way. Evidence for large amounts of dark matter came from the rotating motions of spiral galaxies. A spiral galaxy keeps its size and shape by rotating. Each star in it is orbiting around the center of the galaxy. The speed of rotation depends on the amount of mass inside the orbit. lomoar cpsd| 2151316. More mass = larger speed to compensate for the increased gravitational attraction. The orbital speed is higher for smaller radius r, or bigger mass.
