Composition and equation of state of thermally dissociated matter and mass and stability of rigidly rotating relativistic polytropes

The composition and equation of state of a perfect gas of photons, electrons-positrons, neutrinos, and nucleons are calculated assumming either perfect neutrino transparency or some build up of neutrino concentration in dense matter. The calculations applicable to collapsing stars after thermal dissociation and before nuclear forces are important. The energy of a rigidly rotating star is written in the first and second post-Newtonian approximation. Conditions for equilibrium and stability are derived, as well as evolutionary paths for stars shedding anular momentum or mass. The energy method is applied to low mass white dwarfs, to semi-relativistic neutron stars, and to supermassive stars.