Massive fluid spheres in general relativity

We present a class of nonsingular analytic solutions of the general-relativistic field equations in isotropic form for a static spherically symmetric material distribution. Within a sphere the outward variation of pressure, density, pressure-density ratio, and the adiabatic sound speed is monotonic decreasing. The solution has been used to construct causal models for neutron stars with a maximum mass ≊4$M_{\mathrm{cirdot}}$ where we have assumed a surface density equivalent to the typical terrestrial nuclear density.