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Why is stellar ash found in the core of a White Dwarf so dense?

  1. Sep 29, 2014 #1
    A normal star's core consists of Hydrogen but a white dwarf is itself the core and it consists of stellar ash. So the degeneracy pressure is exerted when this stellar ash becomes very dense (In other words when the white dwarf becomes very dense). Am I right?

    The density of a white dwarf is so much that a small cup of white dwarf material would be equal to the weight of 25 elephants. But why is the stellar ash so dense is another question?
  2. jcsd
  3. Sep 29, 2014 #2

    Ken G

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    It is natural for a self-gravitating gas to get denser and denser as it loses heat. The lost heat causes contraction, and the contraction causes the release of gravitational potential energy, which replaces the lost kinetic energy by even more kinetic energy than before. So as any such object loses heat, it will get denser and have more kinetic energy. This process would normally not end, so the density would get arbitrarily high, as occurs in a supernova that creates a black hole. But quantum mechanics has the Pauli exclusion principle, which means that no two electrons can be in the same state. That limits how dense the gas can get, because after it loses enough heat, the gas approaches its quantum mechanical ground state, and can lose no more heat. So ironically, you do not need quantum mechanics, or what is often called "degeneracy pressure" (not a very good term), to understand why the density is so high-- you need it to understand why the density does not get any higher.
  4. Sep 30, 2014 #3


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    All natural processes extract energy from their environment and leave a lower energy waste product. It's called entropy. The reason the core of a star has high density is because even its gravitational potential energy has been exhausted.
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