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Studyguideanswers4 - 155) Population III stars are the very...

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155) Population III stars are the very first generation of stars containing no metals at all. They are linked to quasars appearing because quasars have very strong absorption lines of ultraviolet rays. Their polarization requires an extreme amount of energy which is accounted for in a generation of massive Population III stars. They are linked to quasars because some of the stars turned into blackholes, which may have in turn formed the cores of the first quasars. Correct 156) There was a lower temperature limit for the first stars forming because molecular hydrogen can’t cool the gas below 200 degrees Kelvin. This cooling was not efficient in more dense clouds because the molecules would collide with one another before they could emit a photon, heating up the clumps and slowing down the collapse process. This allowed stars to reach a few hundred solar masses. Correct 157) The second round of star formation was much more efficient because metals present were efficiently cooling the surrounding gas, allowing for stars with smaller masses to be formed. If a star can be formed at a smaller mass, more can be formed faster than before. Correct 158) The gas became ionized because of early stars giving off ultraviolet radiation. Correct 159) Blue stars can be assumed to be young because they have short lifetimes due to their high mass. Red stars, however, can’t automatically be assumed to be old. Red stars may be old but could also be young and simply low mass, therefore producing red light. Correct 160) Metal is any element other than hydrogen or helium in the universe, from an astronomer’s perspective. Metallicity is the number of metal atoms divided by the total number of atoms present in a cloud of ISM or a star. A main sequence star does not experience a change in its metallicity; it simply has the metallicity of the cloud from which it formed. However, the metallicity of an ISM cloud slowly increases over time due to planetary nebulae, novae, and super novae adding to the metallicity. Correct 161) The metallicity of an old main sequence star would most likely be lower than the metallicity of a young main sequence star because the young star has formed more recently. More recent formation means a more enriched ISM cloud, with a higher metallicity. Correct 164) The metallicity of an older galaxy is likely higher than the metallicity of a young galaxy because in galaxies, the metallicity is determined by combining the metallicities of all of the stars in the galaxy. There are most likely more stars in an older galaxy because they have had time to
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This note was uploaded on 06/14/2008 for the course PHYS 20083 taught by Professor Ingram during the Spring '08 term at TCU.

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Studyguideanswers4 - 155) Population III stars are the very...

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