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A supernova is a stellar explosion that briefly outshines an entire galaxy, radiating as much energy as the Sun or any ordinary star is expected to emit over its entire life span, before fading from view over several weeks or months.〔 〕 The extremely luminous burst of radiation expels much or all of a star's material〔 at a velocity of up to (10% of the speed of light), driving a shock wave〔 〕 into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant. Supernovae fuse and eject the bulk of the primary elements of nucleosynthesis.〔Timmes F.X., Woosley S.E. & Weaver T.A. "Galactic Chemical Evolution" Astrophys. J. Suppl. 98, 617 (1995); D.D. Clayton, ''Handbook of Isotopes in the Cosmos'': Cambridge University Press (2003)〕 They are potentially strong galactic sources of gravitational waves.〔 〕 A great proportion of primary cosmic rays comes from supernovae.〔 〕 Their many significant consequences make supernovae the most important stellar events in astronomy. Supernovae are more energetic than novae. ''Nova'' means "new" in Latin, referring to what appears to be a very bright new star shining in the celestial sphere; the prefix "super-" distinguishes supernovae from ordinary novae, which are far less luminous. The word ''supernova'' was coined by Walter Baade and Fritz Zwicky in 1931.〔 It is pronounced with the plural ''supernovae'' or ''supernovas'' (abbreviated ''SN'', plural ''SNe'' after "supernovae"). Supernovae can be triggered in one of two ways: by the sudden re-ignition of nuclear fusion in a degenerate star; or by the gravitational collapse of the core of a massive star. In the first case, a degenerate white dwarf may accumulate sufficient material from a companion, either through accretion or via a merger, to raise its core temperature, ignite carbon fusion, and trigger runaway nuclear fusion, completely disrupting the star. In the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy that can create a supernova explosion. The most recent directly observed supernova in the Milky Way was Kepler's Star of 1604 (SN 1604); remnants of two more recent supernovae have been found retrospectively.〔 〕 Observations in other galaxies indicate that supernovae should occur on average about three times every century in the Milky Way, and that any galactic supernova would almost certainly be observable in modern astronomical equipment.〔 〕 Supernovae play a significant role in enriching the interstellar medium with higher mass elements.〔 〕 Furthermore, the expanding shock waves from supernova explosions can trigger the formation of new stars.〔〔 〕 ==Observation history== (詳細はHipparchus' interest in the fixed stars may have been inspired by the observation of a supernova (according to Pliny).〔 〕 The earliest recorded supernova, SN 185, was viewed by Chinese astronomers in 185 AD. The brightest recorded supernova was the SN 1006, which was described in detail by Chinese and Islamic astronomers.〔 〕 The widely observed supernova SN 1054 produced the Crab Nebula. Supernovae SN 1572 and SN 1604, the latest to be observed with the naked eye in the Milky Way galaxy, had notable effects on the development of astronomy in Europe because they were used to argue against the Aristotelian idea that the universe beyond the Moon and planets was immutable.〔 〕 Johannes Kepler began observing SN 1604 at its peak on October 17, 1604, and continued to make estimates of its brightness until it faded from naked eye view a year later.〔 〕 It was the second supernova to be observed in a generation (after SN 1572 seen by Tycho Brahe in Cassiopeia).〔 Before the development of the telescope, there have only been five supernovae seen in the last millennium. In the perspective of how long a star's lifetime is, its death is very brief. In fact, a star's death may only last a few months. Due to this, a typical human will only experience this rarity, on average, once in their lifetime. This is a microscopic fraction in comparison to the 100 billion stars that compose a galaxy. Since the development of the telescope, the field of supernova discovery has extended to other galaxies, starting with the 1885 observation of supernova S Andromedae in the Andromeda galaxy. American astronomers Rudolph Minkowski and Fritz Zwicky developed the modern supernova classification scheme beginning in 1941.〔 〕 In the 1960s, astronomers found that the maximum intensities of supernova explosions could be used as standard candles, hence indicators of astronomical distances.〔 〕 Some of the most distant supernovae recently observed appeared dimmer than expected. This supports the view that the expansion of the universe is accelerating.〔 〕 Techniques were developed for reconstructing supernova explosions that have no written records of being observed. The date of the Cassiopeia A supernova event was determined from light echoes off nebulae,〔 〕 while the age of supernova remnant RX J0852.0-4622 was estimated from temperature measurements〔 〕 and the gamma ray emissions from the decay of titanium-44.〔 〕 In 2009, nitrates were discovered in Antarctic ice deposits that matched the times of past supernova events.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「supernova」の詳細全文を読む スポンサード リンク
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