27 how does gas cycle through galaxies 212 arp 220

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27 How does gas cycle through galaxies? 21.2 Arp 220
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The star-gas-star cycle is not always steady. Depends on the rate at which hot gas in halo can cool and resupply the cold clouds necessary to produce stars. Temporary stage 28 21.2 Starburst Galaxies
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Intensity of supernova explosions in starburst galaxies can drive galactic winds. 29 21.2
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A galactic wind in a small galaxy can drive away most of its gas, stopping star formation for a time. X-ray/visible composite photo of dwarf starburst galaxy NGC 1569. X-ray light from the galactic wind is in blue, and visible light from hydrogen gas is shown in red. 30 21.2
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In Summary All galaxies began as active star-forming systems in the blue cloud. Mergers and collisions can produce larger galaxies. Some stop producing stars Some are stripped of gas when entering a cluster. Galaxies with no star formation become redder as their stars age Red sequence 31
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If the center of a galaxy is unusually bright, we call it an active galactic nucleus (AGN). Quasars are the most luminous examples. 32 What is the evidence for supermassive black holes at the centers of galaxies?
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How big are active galactic nuclei? A. about 1000 light-years across B. about 100 light-years across C. about 1 light-year across D. a few light-hours across E. the size of a star 33
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The highly redshifted spectra. Variability shows that all this energy comes from a region smaller than our solar system. 34 21.3
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Thought Question What can you conclude from the fact that quasars usually have very large redshifts? A. They are generally very distant. B. They were more common early in time. C. Galaxy collisions might turn them on. D. Nearby galaxies might hold dead quasars. E. All of the above 35
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What is the luminosity of the most powerful quasars? A. the same as a nova B. the same as a white dwarf supernova C. the same as the Milky Way galaxy D. 80 times the luminosity of the Milky Way galaxy E. 1000 times the luminosity of the Milky Way galaxy 36 From brightness and distance, we find that luminosities of some quasars are greater than 10 12 L Sun .
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Orbital evidence: The orbital speed and distance of gas orbiting the center of Galaxy M87 indicate a black hole with mass of 2–3 billion M Sun .
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  • Fall '19
  • galaxy evolution

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