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final_astro - Astronomy 101 Final Exam Fall 2006 Chapter 11...

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Astronomy 101 Final Exam Fall 2006 Chapter 11 Fill In the Blank 1. The interstellar medium is made up of matter in the form of gas and dust . 2. To scatter a beam of radiation most effectively, a particle must be similar in size to the wavelength of the radiation. 14. It takes a star like the Sun a total of about 1 million years to form. 15. More massive stars evolve more light curves . Review and Discussion 9. Why do stars tend to form in groups? The large interstellar clouds in which stars form are very massive. They fragment into small clouds, each of which eventually forms a star. Therefore a cluster of stars is formed rather than just single stars. 11. What are brown dwarfs? Brown dwarfs occur when a cloud fragment has insufficient mass to form a star. As the gas collapses and the core temperature increases, there is not enough gas to compress and heat the core to 10 million K. Hydrogen fusion never occurs and the object just radiates off its excess energy from formation. This is a brown dwarf. Chapter 12 Fill In the Blank 3. While a star is on the main sequence, hydrogen is slowly consumed in the core and helium builds up. 8. A typical white dwarf has the following properties: about half a solar mass, fairly high surface temperature, small size, and low luminosity. 9. As time goes by, the temperature and the luminosity of a white dwarf both decrease . 10. In a binary consisting of a white dwarf and a main-sequence or giant companion, matter leaving the companion forms an accretion disk around the dwarf. 11. A nova explosion is due to hydrogen fusion on the surface of a white dwarf. 12. When a proton and an electron are forced together, they combine to form a neutron and a neutrino . Review and Discussion 2. Why is the depletion of hydrogen in the core of a star such an important event? <br Without the fusion of hydrogen into helium occurring in the core, the core no longer has an energy source. Gravity is then able to collapse the core, forcing major changes in the entire structure of the star.
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10. Under what circumstances will a binary star produce a nova? The primary factor as to whether stars in a binary will affect one another’s evolution in the separation of the two stars. If separated by a few A.U., most stars will never expand to a sufficiently large size to ever affect each other. 14. What evidence do we have that many supernovae have occurred in our Galaxy? When the supernova explosion occurs, it rapidly ejects a vast cloud of gas. This is called a supernova remnant. Supernova remnants can last for thousands of years and provide evidence of an earlier supernova. Many remnants are observed. 15. Why do the cores of massive stars evolve into iron and not heavier elements? A massive star will eventually build up a core of iron. But iron can not fuse and release energy. The core collapses under gravity; high energy photons break up the iron nuclei. A core of neutrons forms and the remainder of the star explodes as a supernova.
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