Week 12 Galaxies Objectives

Week 12 Galaxies Objectives - dramatically altered the...

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Learning Objectives for Week 12 Galaxies 1. When galaxies were first discovered, it was not clear that they lie far beyond the Milky Way. As late as the 1920s it was unclear whether spiral nebulae were very remote “island universes” or simply nearby parts of our Galaxy. 2. Hubble proved that the spiral nebulae are far beyond the Milky Way. Cepheid variables revealed the immense distances to other galaxies. 3. Hubble devised a system for classifying galaxies according to their appearance. Galaxies come in various shapes: spiral, barred spiral, elliptical, and irregular. 4. Galaxies are grouped into clusters and superclusters. Superclusters of galaxies are not spread uniformly across the universe, but are found in vast sheets separated by truly immense voids. 5. Colliding galaxies produce starbursts, spiral arms, and other spectacular phenomena. Galaxies need not actually collide to exert strong forces on each other. 6. Galaxies formed from the merger of smaller objects. Over the eons, collisions and mergers have
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Unformatted text preview: dramatically altered the population of galaxies. 7. Active galaxies bridge the gap between normal galaxies and quasars. Fast-moving jets emanate from quasars, radio galaxies, and Seyfert galaxies. 8. Quasars look like stars but have huge redshifts. Examining the spectra of quasars revealed that they are immensely distant. 9. Quasars are the ultraluminous centers of distant galaxies. The most luminous quasars emit 100,000 times more radiation than the entire Milky Way Galaxy. 10. Supermassive black holes are the central engines that power active galaxies. Most or all large galaxies have supermassive black holes at their centers. 11. Quasars, blazars, and radio galaxies are probably the same kind of object seen from different angles. The power source for active galaxies is gravitational energy released by material falling toward a central black hole....
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