Chapter_19_Milky_Way_summary - Doppler-velocity...

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Chapter Summaries Chapter 19: The Milky Way (19.1, 19.3, 19.4) (don’t forget to find definitions at the end of the book, in the glossary and draw pictures!!!!!) 1. Our galaxy consists of a disk of stars and gas, with a bulge of stars at the center of the disk, surrounded by a large spherical halo disk bulge halo (Halo stars are all old, with a smaller proportion of heavy elements than disk stars, indicating that the halo formed first) 2. Stars in the disk orbit in circles going in the same direction with a little up-and-down motion 3. Orbits of halo and bulge stars have random orientations 4. Sun’s location is in an arm in the outer part of the Milky Way.
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Unformatted text preview: Doppler-velocity measurements tell us we live in a spiral galaxy 5. Orbits of stars near the center of our galaxy indicate that it contains a black hole with 4 million times the mass of the Sun 6. Best hypothesis for how galaxies form: 1. A giant cloud of H and He condensed after the Big Bang 2. Halo stars (oldest) formed first, in clumps, as gravity caused cloud to contract. These clumps later merged. 3. Bulge stars form next 4. Remaining gas settled into spinning disk 5. Star formation continues as long as there is material in the ISM (interstellar medium) (stars continuously form in disk as galaxy grows older)...
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