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Unformatted text preview: These lecture notes were prepared for Rutgers Physics 341/342: Principles of Astrophysics by Prof. Chuck Keeton, and modified by Profs. Saurabh Jha and Eric Gawiser. All rights reserved. c 2011 Lecture 13: Galaxies There is much to say about galaxies! Here at Rutgers, Physics 443 is a whole course devoted to galaxies. For this course I want to focus on their internal motion, or dynamics , and what it tells us about their mass. The book begins the study of galaxies with the Milky Way. However, there are many complications arising from the fact that we are inside the Galaxy, making to hard to observe the Galaxys properties. This is a classic case of not seeing the forest for the trees! So I will focus on other galaxies, but attempt to put the Milky Way in context. I. The Nature of Galaxies (See Chapter 25 of Carroll & Ostlie.) Hundreds of thousands of galaxies have been observed; see http://thegalaxyzoo.org for examples. It is natural to try to classify them to look for patterns, and group similar galaxies together. There seems to be three main categories: spiral galaxies: disk, spiral arms, bulge (and maybe a bar); contain stars, gas, and dust elliptical galaxies: smooth, featureless, ellipsoidal distribution of light; contain mostly stars (little gas and dust) irregular galaxies: everything else! The spiral galaxies are further subdivided by the appearances of the disk, spiral arms, bulge, and bar. (Show pictures in class.) Edwin Hubble came up with a scheme to organize the galaxy types at least the spirals...
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- Fall '11