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Degeneracy pressure of a White Dwarf Star

  • #1

Homework Statement:

A stable white dwarf star has mass m = 10^30 kg and radius R = 8 ×10^8 m. What is the degeneracy pressure of the electron gas in the star?

Relevant Equations:

P = 2πc/3h^3 × P(F)^4 × [1 - {mc/P(F)}^2]
where P(F) = h(3N/8πV)^(1/3)
So far, I am provided with all the required values for calculation, except N.
If N = total number of electrons in star, then using N = mass of star/ mass of an electron should be no problem.
Am I right?
 

Answers and Replies

  • #2
SammyS
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Homework Statement:: A stable white dwarf star has mass m = 10^30 kg and radius R = 8 ×10^8 m. What is the degeneracy pressure of the electron gas in the star?
Relevant Equations:: P = 2πc/3h^3 × P(F)^4 × [1 - {mc/P(F)}^2]
where P(F) = h(3N/8πV)^(1/3)

So far, I am provided with all the required values for calculation, except N.
If N = total number of electrons in star, then using N = mass of star/ mass of an electron should be no problem.
Am I right?
That can't be right.

That would work if the white dwarf star were composed entirely of electrons.
 
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  • #3
That can't be right.

That would work if the white dwarf star were composed entirely of electrons.
I think N is given by: N = M/(2×Mass of a proton)
 
  • #4
SammyS
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I think N is given by: N = M/(2×Mass of a proton)
That may make sense.

What is the typical composition of a white dwarf star?
 
  • #5
Sir usually WDSs are mainly composed of C-12 & O-16.
But the question here is asking about electron gas.
 
  • #6
SammyS
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Sir usually WDSs are mainly composed of C-12 & O-16.
But the question here is asking about electron gas.
Right. Each of those atoms has 1 electron for every two nucleons (one proton & one neutron). So, yes you were essentially right when you wrote: N = M/(2×Mass of a proton) .
 
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