Degeneracy, white dwarfs and neutron stars

4 Degeneracy, white dwarfs and neutron stars 5.4.1 Introduction 

Examination of the Fermi-Dirac distribution function Eq. (2.41) shows that the condition for applicability of the ideal-gas distribution to electron velocities is 

When thermal energy is negligible, cells in phase space are uniformly occupied up to the Fermi momentum pp, given by 

Because at this stage the material has usually been processed into helium and heavier elements, electrons outnumber nuclei and make the dominant contribution to the pressure, the more so when their energy from degeneracy greatly exceeds kT it is 

There is a critical density /)cnt above which the electrons become relativistic, i.e. 

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