The Complex Relationship Between Mass & Volume in a White Dwarf

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SUMMARY

The discussion centers on the relationship between mass and volume in white dwarfs, specifically how the mass is inversely proportional to volume. The rate of change of the number of electrons with energy (dN/dE) is derived from the density of states function g(E) = kE^(0.5), leading to the conclusion that dN/dE becomes inversely related to the mass of the white dwarf. This relationship challenges the expectation that increased mass would correlate with an increase in the number of electrons. The temperature within a white dwarf, approximately 10^7K, affects the distribution function f(E), which approaches 1 as volume decreases and mass increases, complicating the understanding of electron distribution as the star cools.

PREREQUISITES
  • Understanding of quantum mechanics and potential wells
  • Familiarity with the concept of density of states in statistical mechanics
  • Knowledge of thermodynamic principles, particularly in high-temperature environments
  • Basic astrophysics, specifically the characteristics of white dwarfs
NEXT STEPS
  • Study the implications of the Pauli exclusion principle in electron distribution
  • Explore the effects of temperature on electron behavior in stellar environments
  • Investigate the cooling processes of white dwarfs and their impact on mass and volume
  • Learn about the equations governing stellar structure, particularly in degenerate matter
USEFUL FOR

Astronomers, astrophysicists, and students studying stellar evolution, particularly those interested in the properties and behaviors of white dwarfs.

vin300
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We have the rate of change of number of electrons with energy directly proportional to the volume in an 3-D potential well.
For a white dwarf, the mass is inversely proportional to its volume.

If we consider the electrons in a white dwarf to be in such a potential well, dN/dE becomes inversely proportional to the mass of the white dwarf which,to me, is hard to digest because with more mass the number of electrons is supposed to increase.
 
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g(E)=kE^(0.5)
g(E) is the density of states, k a constant and E the energy of the state.
dN/dE =kVE^(0.5)
dN/dE is the rate of change of number of electrons with energy.
For a white dwarf,
R=(3.6*10^19)/M^(1/3)
where R is the radius and M the mass of the wd.
Since its volume is in inverse proportion to its mass, dN/dE becomes inversely related to the latter.But dN/dE is supposed to be directly proportional to its mass so that integration over all the energy levels gives more free electrons.
 
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I got it.The temperature inside of a white dwarf is about 10^7K, at such temperatures, the distribution function given by
f(E)= [exp(E-Ef)/kT +1]^-1 is approximately 1 for all states, so integration of f(E)g(E)dE gives more electrons per unit volume.
As the volume of the white dwarf lowers, its mass rises, temperature rises bringing f(E) closer to 1.
That doesn't seem correct either.What after the white dwarf has cooled ? :frown:
 
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