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Joined:	29 Nov 2011
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23 Mar 2012 22:19:56 IST

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why do white dwarfs glow brightly??

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they are formed when a star runs out of its fuel, then how does it glows?

is a black hole immortal.......? if it ends -HOW?

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Vishal Mahuli

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Joined: 14 Feb 2012

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25 Mar 2012 11:37:27 IST

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Itsnot formed when astar gets out of its fuel completely,.... its just a progressive stage of STAR DEATH.... so what all amount of energy is left is sent out in the form of light........ yaa black hole is immortal....

edison

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Joined: 19 Oct 2006

Posts: 7797

29 Mar 2012 12:26:50 IST

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A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored thermal energy.

Electron degeneracy is a stellar application of the Pauli Exclusion Principle, as is neutron degeneracy. No two electrons can occupy identical states, even under the pressure of a collapsing star of several solar masses. For stellar masses less than about 1.44 solar masses, the energy from the gravitational collapse is not sufficient to produce the neutrons of a neutron star, so the collapse is halted by electron degeneracy to form white dwarfs. This maximum mass for a white dwarf is called the Chandrasekhar limit. As the star contracts, all the lowest electron energy levels are filled and the electrons are forced into higher and higher energy levels, filling the lowest unoccupied energy levels. This creates an effective pressure which prevents further gravitational collapse.

Sirius-B gives an example of the size of a white dwarf. Electron degeneracy halts the collapse of this star at the white dwarf stage. Though comparable in mass to the Sun, its white dwarf stage is smaller than the Earth.

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