They aren't really, except at the level of approximation that comes about from a simple estimate of what degeneracy pressure does. The Chandrasekar Limit for white dwarfs is 1.4 solar masses, and the Oppenheimer-Volkov limit for neutron stars is 1.4 solar masses. These stellar cinders are supported by electron degeneracy pressure (white dwarfs) and neutron degeneracy pressure (neutron stars) which are two very different mechanisms. Both forces are expressed by essentially the same formula, except that the strong nuclear force is 100 times more than the electromagnetic force, and this causes the size of the neutron star to be much smaller than a white dwarf ( 10,000 km vs 20 km). Even though the pressure comes from the light-weight electrons in white dwarfs, the mass of the body is still determined by the number of protons and neutrons. The relationship that defines this maximum mass depends only on the fundamental constants, c, G, h according to:
3/2
(hc)
M = -----------
3/2 3/4
G m
Where m is the mass of a proton.
The maximum mass of a neutron star is, however, a bit more complicated that what is suggested by the Oppenheimer-Volkov limit and depends on the details of the rotation of the neutron star, and the specific 'equation of state' used to describe matter at densities of 10^13 grams/cc or higher. Upper limits for rotating neutron stars can be as high as 3 times the mass of the Sun.
Copyright 1997 Dr. Sten Odenwald
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