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White dwarfs and degeneracy

  1. Jan 28, 2012 #1
    Yesterday i had a thought about when our sun runs out of energy and collapses into a white dwarf, it is my understanding when this happens a white dwarf is held up by electron degeneracy, all the electrons are under immense pressure but cannot fall to the lowest energy state therefore stopping the star from collapse due to gravity.
    My question is how can this star still emit light as the electrons cannot change energy levels?
    Unless my understanding of degeneracy is wrong and they can in fact change energy levels, if this is the case would anyone care to explain?

    thanks
     
  2. jcsd
  3. Jan 28, 2012 #2

    Bill_K

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    At absolute zero the degeneracy is complete. All the states up to the Fermi level are occupied, and particles are unable to move from one state to another. (Electrons in a white dwarf, neutrons in a neutron star.) But at a finite temperature some of the particles are excited above the Fermi level, leaving vacancies, where some of them interact with other particles, such as photons.
     
  4. Jan 28, 2012 #3
    [QUOTEAt absolute zero the degeneracy is complete. All the states up to the Fermi level are occupied, and particles are unable to move from one state to another. (Electrons in a white dwarf, neutrons in a neutron star.) But at a finite temperature some of the particles are excited above the Fermi level, leaving vacancies, where some of them interact with other particles, such as photons.][/QUOTE]

    Is it the immense pressure that is causing this high temperature creating interactions?
     
  5. Jan 28, 2012 #4
    I think the degeneracy only occurs in the lower levels of the white dwarf, whereas on the upper levels and with the atmosphere on the surface electrons can still move.
     
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