Prob physics (2)

Prob physics (2) - A supernova (abbreviated SN, plural SNe...

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A supernova (abbreviated SN, plural SNe after supernovae) is a stellar explosion that is more energetic than a nova . It is pronounced / ˌ s u ː p r ə ˈ n o ʊ v ə / with the plural supernovae / ˌ s u ː p r ə ˈ n o ʊ v i ː / or supernovas . Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy , before fading from view over several weeks or months. During this short interval a supernova can radiate as much energy as the Sun is expected to emit over its entire life span. [1] The explosion expels much or all of a star's material [2] at a velocity of up to 30,000 km/s (10% of the speed of light ), driving a shock wave [3] into the surrounding interstellar medium . This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant . Nova (plural novae ) 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 also involve a star increasing in brightness, though to a lesser extent and through a different mechanism. The word supernova was coined by Walter Baade and Fritz Zwicky in 1931. [4] Several types of supernovae exist. Types I and II can be triggered in one of two ways, either turning off or suddenly turning on the production of energy through nuclear fusion . After the core of an aging massive star ceases generating energy from nuclear fusion, it may undergo sudden gravitational collapse into a neutron star or black hole , releasing gravitational potential energy that heats and expels the star's outer layers. Alternatively a white dwarf star may accumulate sufficient material from a stellar companion (either through accretion or via a merger) to raise its core temperature enough to ignite carbon fusion , at which point it undergoes runaway nuclear fusion, completely disrupting it. Stellar cores whose furnaces have permanently gone out collapse when their masses exceed the Chandrasekhar limit , while accreting white dwarfs ignite as they approach this limit (roughly 1.38 [5] times the solar mass ). White dwarfs are also subject to a different, much smaller type of thermonuclear explosion fueled by hydrogen on their surfaces called a nova. Solitary stars (such as the Sun) with a mass below approximately 9 solar masses, evolve into white dwarfs without ever becoming supernovae. Although no supernova has been observed in the Milky Way since 1604 , supernovae remnants indicate that on average the event occurs about once every 50 years in the Milky Way. [6]
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This note was uploaded on 03/27/2012 for the course PHYS 101 taught by Professor Schermerhorn during the Spring '12 term at CUNY Brooklyn.

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Prob physics (2) - A supernova (abbreviated SN, plural SNe...

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