Wikipedia:Today's featured article/August 3, 2007

A supernova is a stellar explosion that creates an extremely luminous object that is initially made of plasma—an ionized form of matter. A supernova may briefly outshine its entire host galaxy before fading from view over several weeks or months. During this brief period of time, the supernova radiates as much energy as the Sun would emit over about 10 billion years. The explosion expels much or all of a star's material at a velocity of up to a tenth the speed of light, driving a shock wave into the surrounding interstellar gas. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant. There are several types of supernovae and at least two possible routes to their formation. A massive star may cease to generate energy from the nuclear fusion of atoms in its core, and collapse under the force of its own gravity to form a neutron star or black hole. Alternatively, a white dwarf star may accumulate material from a companion star (either through accretion or a collision) until it nears the Chandrasekhar limit of roughly 1.44 times the mass of the Sun, at which point it undergoes runaway nuclear fusion in its interior, completely disrupting the star. On average, supernovae occur about once every 50 years in a galaxy the size of the Milky Way and play a significant role in enriching the interstellar medium with heavy elements. Furthermore, the expanding shock waves from supernova explosions can trigger the formation of new stars. (more...)

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