98 lines
5.8 KiB
Plaintext
98 lines
5.8 KiB
Plaintext
ÜÜÜÜÜÜÜÜÜÜÜÜÜ ÜÜÜ ÜÜÜÜ
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ÜÛÛÛÛÛÛÛÛßÛßßßßßÛÛÜ ÜÜßßßßÜÜÜÜ ÜÛÜ ÜÛÛÛÛÛÛÛÛÜÜÜÜÜÛßß ßÛÛ
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ßÛÛÛÛÛÛÛÛÛÛÛÛÛÛÜ ßÛÛ ÜÛÛÛÜÛÛÜÜÜ ßÛÛÛÛÜ ßÛÛÛÛÛÛÛÜÛÛÜÜÜÛÛÝ Ûß
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ßßßÛÛÛÛÛÛÛÛÛÛÜ ÞÝ ÛÛÛÛÛÛÛÛÛÛÛßßÛÜÞÛÛÛ ÛÛÛÛÛÜ ßßÛÛÛÞß
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Mo.iMP ÜÛÛÜ ßÛÛÛÛÛÛÛÝÛ ÞÛÛÛÛÛÛÛÛÛ ÞÛÛÛÛ ÞÛÛÛÛÛÝ ßÛß
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ÜÛÛÛÛÛÛÛ ÛÛÛÛÛÛÛÛÝ ÞÛÛÛÛÛÛÛÛÝ ÛÛÛ ÛÛÛÛÛÛ
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ÜÛÛÛÛÛÛÛÝ ÞÛÛÛÛÛÛÛÛ ÞÛÛÛÛÛÛÛÛ ß ÞÛÛÛÛÛÛÜ ÜÛ
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ÜÛÛÛÛÛÛÛÝ ÛÛÛÛÛÛÛÛ ÛÛÛÛÛÛÛÛÝ ÞÞÛÛÛÛÛÛÛÛÛß
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ÜÛßÛÛÛÛÛÛ ÜÜ ÛÛÛÛÛÛÛÛÝ ÛÛÞÛÛÛÛÛÝ ÞÛÛÛÛÛÛßß
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ÜÛßÛÛÛÛÛÛÜÛÛÛÛÜÞÛÛÛÛÛÛÛÛ ÞÛ ßÛÛÛÛÛ Ü ÛÝÛÛÛÛÛ Ü
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ÜÛ ÞÛÛÛÛÛÛÛÛÛÛß ÛÛÛÛÛÛÛÛÛ ßÛÜ ßÛÛÛÜÜ ÜÜÛÛÛß ÞÛ ÞÛÛÛÝ ÜÜÛÛ
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ÛÛ ÛÛÛÛÛÛÛÛß ÛÛÛÛÛÛÛÛÛÛÜ ßÛÜ ßßÛÛÛÛÛÛÛÛÛß ÜÜÜß ÛÛÛÛÜÜÜÜÜÜÜÛÛÛÛÛß
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ßÛÜ ÜÛÛÛß ßÛÛÛÛÛÛÛÛÛÛÜ ßßÜÜ ßßÜÛÛßß ßÛÛÜ ßßßÛßÛÛÛÛÛÛÛßß
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ßßßßß ßßÛÛß ßßßßß ßßßßßßßßßßßßß
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ARRoGANT CoURiERS WiTH ESSaYS
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Grade Level: Type of Work Subject/Topic is on:
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[ ]6-8 [ ]Class Notes [Essay on SuperNova's. ]
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[x]9-10 [ ]Cliff Notes [ ]
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[ ]11-12 [x]Essay/Report [ ]
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[ ]College [ ]Misc [ ]
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Dizzed: 12/94 # of Words:714 School: ? State: ?
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ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>Chop Here>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ
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supernova
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A supernova is a STAR that explodes. It suddenly increases in
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brightness by a factor of many billions, and within a few weeks it slowly
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fades. In terms of the human lifespan, such explosions are rare
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occurrences. In our Milky Way galaxy, for example, a supernova may be
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observed every few hundred years. Three such explosions are recorded in
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history: in 1054, in 1572, and in 1604. The CRAB NEBULA consists of
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material ejected by the supernova of 1054. Such materials, known as
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supernova remnants, are common in the heavens.
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The supernovas observed in modern times have all occurred in other
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galaxies, the most distant yet having been detected in 1988 in a galaxy 5
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billion light-years away. The most interesting supernova of recent times
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was detected in the relatively nearby Large MAGELLANIC CLOUD, on Feb. 23,
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1987, by an astronomer at Chile's Las Campanas Observatory. It quickly
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became an object of intense study by all the means available to modern
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astronomy.
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A supernova may radiate more energy in a few days than the Sun does in
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100 million years, and the energy expended in ejecting material is much
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greater even than this. In many cases, including the Crab nebula supernova,
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the stellar remnant left behind after the explosion is a NEUTRON STAR--a
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star only a few kilometers in diameter having an enormously large density
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and consisting mainly of neutrons--or a PULSAR, a pulsating neutron star.
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There are two common types of supernovas, called type I and type II.
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Type I occurs among old stars of small mass, whereas type II occurs among
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very young stars of large mass. It is not known how a small-mass star can
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release the very large amounts of energy needed to explain type I
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supernovas. Scientists generally believe that this must involve binary
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systems--two stars revolving around each other. In such a system one of the
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stars is a WHITE DWARF, a small, dense star that is near the end of its
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nuclear burning phase. After attracting matter from the companion star for
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some time, the white dwarf eventually collapses with a great rush, becoming
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a neutron star, and ejecting matter outward. This rebound of matter is
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thought to be the supernova.
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Stars with large masses burn their nuclear fuel very rapidly. Within a
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million years or less, such stars build cores containing much iron. When
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the iron eventually burns, energy is quickly drained from the core, and the
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star cannot continue to support itself against gravity. It suffers a mighty
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collapse analogous to that of a type I supernova, and the rebound causes
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matter to be ejected in a type II supernova explosion. Stars ending in this
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way are typically red SUPERGIANTS, but the one that exploded as 1987A was a
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blue star, named Sanduleak, with a mass only about 15 times that of the
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Sun. Its pattern of brightening and fading also varied notably from that of
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typical type II supernovas, and an as yet unexplained "mystery spot"
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appeared some time after the explosion, apparently near to Sanduleak's
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former location. In 1989 astronomers thought that they had detected an
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extremely fast-spinning pulsar at that location, but much further data is
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still needed before this finding is confirmed.
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Cosmologists estimate that the Universe came into existence about 15
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billion years ago. This involved the initial creation of hydrogen and
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helium. Since then nuclear fusion in stars has changed some of the original
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hydrogen and helium into heavier elements (see STELLAR EVOLUTION).
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Supernovas have played an important role both in producing the heavy
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elements and in ejecting material back into space, where it has been used
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to make new stars and, probably, PLANETARY SYSTEMS. It is possible that one
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or more supernovas exploded shortly before the formation of our solar
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system. Elements ejected from these explosions could have mixed with the
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solar nebula, eventually becoming part of the structures of the Sun, the
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Earth, and all living things.
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Bibliography: Clark, D. W., and Stephenson, F. R., eds.,
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Historical Supernovae (1977); Jastrow, Robert, and Thompson,
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Malcolm, Astronomy (1984); Marschall, Laurence A., The
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Supernova Story (1988); Murdin, Paul and Leslie, Supernovae
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(1985); Shy, Frank, The Physical Universe (1982); Woosley,
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Stan, and Weaver, Tom, "The Great Supernova of 1987,"
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Scientific American, August 1989; Zeilik, Michael, and Gaustad,
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John, Astronomy (1983).
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