The Complex Relationship Between Mass & Volume in a White Dwarf

In summary, the rate of change of the number of electrons with energy in a 3-D potential well is directly proportional to the volume. For a white dwarf, the mass is inversely proportional to its volume. This means that the rate of change of electrons with energy is inversely related to the mass of the white dwarf. However, at high temperatures, the distribution function and density of states lead to an increase in the number of free electrons. As the white dwarf cools, the mass increases and the temperature decreases, resulting in a decrease in the number of free electrons.
  • #1
vin300
603
4
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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  • #2
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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  • #3
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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Related to The Complex Relationship Between Mass & Volume in a White Dwarf

1. What is a white dwarf?

A white dwarf is a type of star that has reached the end of its life cycle and has exhausted all of its nuclear fuel. It is the remnant core of a low to medium mass star, typically composed of carbon and oxygen.

2. How does mass affect the size of a white dwarf?

The more massive a white dwarf is, the smaller it will be. This is because the gravitational force is directly proportional to the mass, so a higher mass star will have a stronger gravitational pull, causing it to shrink in size.

3. What is the relationship between mass and volume in a white dwarf?

In a white dwarf, there is an inverse relationship between mass and volume. As the mass increases, the volume decreases. This is due to the fact that the star's gravity becomes stronger as it loses mass, causing it to compress and become denser.

4. How does volume affect the temperature of a white dwarf?

The volume of a white dwarf is directly related to its temperature. As the volume decreases and the star becomes more compact, the temperature of the core increases. This is because the star's internal pressure increases, causing the temperature to rise.

5. Can the mass and volume of a white dwarf change?

The mass and volume of a white dwarf remain relatively constant once it has reached the end of its life cycle. However, if it is in a binary system with another star, it can gain or lose mass through accretion from its companion. This can affect its volume and temperature, but the overall relationship between mass and volume remains the same.

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