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A supernova is a type of stellar explosion which appears to result in the creation of a new star upon the celestial sphere. ("Nova" is Latin for "new"). The "super" prefix distinguishes this from a nova, which also involves a star increasing in brightness, though to a lesser extent and through a different mechanism. Supernovae involve the expulsion of a star's outer layers; filling the surrounding space with hydrogen and helium (along with other elements); the debris eventually forms clouds of dust and gas. When the explosion of a supernova compresses nearby clouds, it can induce their gravitational collapse to form new stars, and enrich those new stars in heavy elements.
Supernovae can release several times joules of energy, roughly equivalent to the output of the SunThe Sun (also called Sol is the star in our solar system. Planet Earth orbits the Sun. Other bodies that orbit the Sun include other planets, asteroids, meteoroids, comets and dust. Not all objects passing through the solar system have been orbitally capt over its entire lifetime.
As part of the attempt to understand supernova explosions, astronomers have classified them according to the lines of different chemical elements that appear in their spectraSpectroscopy is the study of spectra, ie. the dependence of a physical measure to frequency. Spectroscopy is often used in physical and analytical chemistry for the identification of substances, through the spectrum emitted or absorbed. A device for recor. See "Optical Spectra of Supernovae" by Filippenko (Annual Review of Astronomy and Astrophysics, Volume 35, 1997, pp. 309-355) for a good description of the classes.
The first element for division is the presence or absence of a line from hydrogen. If a supernova's spectrum does not contain a hydrogen line, it is classified Type I, otherwise Type II.
Among those groups, there are subdivisions according to the presence of other lines and the shape of its light curve.
Type Ia supernovae lack helium and present a siliconSilicon is the chemical element in the periodic table that has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon. It is the second most abundant element in the Earth's crust, making up 25 absorption line in their spectra near peak light. The most commonly accepted theory of these type of supernovae is that they are the result of a carbon- oxygen white dwarf accreting matter from a nearby companion star, typically a red giant, until it reaches the Chandrasekhar limit. The increase in pressure from the resultant collapse of the star ignites carbon fusion in the star's core. This in turns causes the star to explode violently and to release a shock wave in which matter is typically ejected at speeds on the order of 10,000 km/s. The energy released in the explosion also causes an extreme increase in luminosity.
The theory of these type of supernovae is similar to that of novae, in which a white dwarf accretes matter more slowly and does not reach the Chandrasekhar limit. In the case of a nova, the infalling matter causes a fusion reaction of material near its surface but does not cause the star to collapse.
Type Ia supernovae have a characteristic light curve (graph of luminosity as a function of time after the explosion). Near the time of maximum luminosity, the spectrum contains lines of intermediate-mass elements from oxygen to calcium; these are the main constituents of the outer layers of the star. Months after the explosion, when the outer layers have expanded to the point of transparency, the spectrum is dominated by light emitted by material near the core of the star: heavy elements synthesized during the explosion, most prominently iron-group elements. The radioactive decay of Nickel-56 through Cobalt-56 to Iron-56 produces high-energy photons which dominate the energy output of the ejecta at intermediate to late times.
Unlike the other types of supernove, Type Ia supernovae are generally found in all types of galaxies, including ellipticals. They show no preference for regions of current star formation.
The similarity in the shapes of the luminosity profiles of all known Type Ia supernovae has led to their use as a standard candle in extragalactic astronomy. The cause of this similarity in the luminosity curve is still an open question mark. In the late 1990s, observations of type Ia supernovae produced the unexpected result that the universe seems to undergo an accelerating expansion.
The Type Ia supernova releases the highest amounts of energy amongst all known classifications of supernovae. The farthest single object ever detected in the universe ( galaxies or globular clusters do not count) was a Type Ia supernova located billions of light-years away.
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