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Study Guide #3 - Study Questions Guide#3(F07 GEOL 125 Earth...

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Study Questions Guide #3 (F07) GEOL 125: Earth History Dr. Hammond Draw a Hertzsprung-Russell diagram and indicate the positions of main sequence stars, red giants, white dwarfs, and our sun. How does a star of solar mass evolve on this diagram? What are the energy sources for stars in different parts of this diagram? The luminosity of a star can be determined from its brightness and distance, and its surface temperature can be found can be found from color. When luminosity (on a log scale) is plotted against surface temperature (on a log scale), most stars fall into one of several groupings. The largest is the main sequence . A few stars have a low surface temperature (with max emission at red wavelengths), but emit large amounts of energy. In order to be so luminous, they must be very large. These stars are called Red Giants. Others have a relatively high surface temperature but a low luminosity; these must be very small and are called White Dwarfs. A few stars have both high temperature and high luminosity and are called Supergiants . Why is a mass of at least 0.1 solar masses necessary for a star to form? How does the lifetime of a star depend on mass? How long will the sun exist in its present form? What will be the fate of our sun? What are the stages in the life of a massive star? What is the likely fate of a star of 10 solar masses? A mass of at least 0.1 (times the size of our sun) is necessary for a star to form because the dust cloud needs to have sufficient mass to achieve temperatures and densities in its center that are sufficient to initiate H fusion. (This makes a star born). Reaches critical density which causes the dust cloud to collapse. How much mass is in a dust cloud, determines how hot it will get in the center of a dust cloud which starts fusion. The rate at which a star passes through the various stages increases with increasing stellar mass with empirical evidence that lifetime is approx. proportional to - . m 2 5 . (The bigger the star, the faster it ages.) It may take about 50 my for the sun to reach the main sequence stage. The sun will exist in its present form for another 5 by. At this point, our sun will turn into a red giant and swallow the earth because the sun will run out of hydrogen. Stages in Life of Massive Star: 1. Dust cloud exceeds critical density and collapses (supernova trigger) 2. Cloud heats (gravitational potential energy kinetic energy thermal energy) 3. Cloud spins faster and flattens (conserves angular momentum) 4. The temperature at center rises enough to initiate fusion (a star is born)
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5. Inner solar nebula is hot, but outer is cool. Silicates an iron condensed into grains, but volatile elements remain as gasses. Outer nebula is cold and all elements form grains. 6. Young star T-Tauri phase: sweeps away gasses and gives off volatile gasses.
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