  We reconsider the problem of modelling static spherically symmetric perfect
fluid configurations with an equation of state from a point of view of that
requires the use of the concept of principal transform of a 3-dimensional
Riemannian metric. We discuss from this new point of view the meaning of those
familiar quantities that we call density, pressure and geometry in a
relativistic context. This is not simple semantics. To prove it we apply the
new ideas to recalculate the maximum mass that a massive neutron core can have.
This limit is found to be of the order of 3.8 $M_\odot$ substantially larger
than the Oppenheimer and Volkoff limit.
