Stargazing Understanding the Chandrasekhar Mass Units for Relativistic Lane Emden Equations

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The discussion centers on calculating the Chandrasekhar mass using the relativistic Lane Emden equation with n = 3, leading to the conclusion that Mtotal is proportional to a³. A participant points out a potential dimensional inconsistency in the equation K = P/ρ^(1+1/n), suggesting it yields dimensions of [M]^(2/3) rather than [M]². The confusion arises from a symbol clash involving 'a', which is clarified as part of the Lane Emden equations. The original poster acknowledges their mistake and decides not to delete the thread, recognizing its value for others. The conversation highlights the importance of accurate dimensional analysis in astrophysical calculations.
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TL;DR Summary
relativistic equation for mass give incorrect units using Lame Emden
Using Lane Emden and n = 3 (relativistic), I calculate the correct mass -- the Chandrasekhar mass (about 1.4 Msun)
The equation goes Mtotal ∝ a3, because at n=3, the density, ρ, cancels out.
a2 ∝ K/G = Kg2 → a3 ∝ Kg3. Here K ∝ h c or Kg m3/sec2 and G ∝ m3/Kg/sec2
This implies the mass, Mtotal units is Kg3

What is wrong, please...
 
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A reference would be helpful. Looking at the Wikipedia page, ##K=P/\rho^{1+1/n}##, which is ##P\rho^{-4/3}## in your case. That does not seem to me to have dimensions of ##\mathrm{[M]}^2##, but rather ##\mathrm{[M]}^{2/3}## if my late night algebra is correct. But that page doesn't mention a symbol ##a## anywhere, so it may be a symbol clash - which is why a reference would be helpful.
 
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Ibix said:
A reference would be helpful. Looking at the Wikipedia page, ##K=P/\rho^{1+1/n}##, which is ##P\rho^{-4/3}## in your case. That does not seem to me to have dimensions of ##\mathrm{[M]}^2##, but rather ##\mathrm{[M]}^{2/3}## if my late night algebra is correct. But that page doesn't mention a symbol ##a## anywhere, so it may be a symbol clash - which is why a reference would be helpful.
Thank you - I discovered my mistake. I will delete this post shortly.
 
a is in Lame Emden equations --- as in, r = a ξ
 
I guess I can't delete...
 
MarkL said:
I guess I can't delete...
No reason to delete the thread -- it has value to others. I'll go ahead and tie it off for you. :smile:
 
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