Application of continuous variation formulas and discrete invariance principles to black holes and neutron star models

A discussion is given of the inferences that can be drawn from the application of the principle of time reversal invariance to the equilibrium states of axisymmetric bodies in general relativity, in conjunction with the law relating energy and angular momentum variations in elastic deformations. The concepts of moments of inertia and of the mutual moments of inertia between different components of a multicomponent body are described. Particular attention is given to the case of axisymmetric perfect solid neutron star models with relaxable elastic structures, and it is shown that such bodies have equilibrium states with the special property of invariance under simultaneous time and axial angle reversal. Finally, the case of a Kerr black hole is presented as a concrete example of the application of the ensuing formulas.