The core cannot be supported by electron degeneracy, and collapse down until neutron degeneracy takes over. Neutrons are fermions, and subject to the Pauli exclusion principle just like electrons were.
How massive are neutron stars? Typically, about 1.4 Msun, the Chandrasekhar mass. Why??
Because they are supported by (neutron) degeneracy, they also follow a mass-radius relationship similar in behavior to that of white dwarfs (R~M-1/3), but at much smaller sizes:
Past this? Black holes....
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Conservation of angular momentum as the core collapses:They have very strong magnetic fields!Or, for a sphere of constant structure,
So the final spin frequency is
or the final spin period is
What is the initial rotation period? Not certain, but for an example, let's use the rotation period of a nearby white dwarf: 1350 seconds. Then the rotation period of the neutron star will be PNS ~ 5x10-3 seconds!
Magnetic flux (B times area) through the surface of the core is also conserved in collapse. SoThey are hot!Which means that
Again, using the magnetic field strength of an extreme white dwarf, B=5x108 Gauss, BNS ~ 1014 Gauss! Compare to the Sun, which has a magnetic field strength of 2 Gauss.
The temperature of their creation (in a supernova) is 1011 K. They rapidly cool by neutrino emission down to a temperature of 106 K (in a thousand years or so).Hmm, tiny, X-ray emitting neutron stars. Could we ever see them?Stefan-Boltzmann: L = 4piR2sigmaT4 = 7x1032 erg/s. Like the Sun.
Easy to see? Nope: LambdaMax = 0.29/T ~ 29 Angstroms -- X-rays!