Nonsingular Spherical Models with a Variable Cosmological term

Abstract

Exact solutions of the Einstein's field equations describing a spherically symmetric cosmological model without a big bang or any other kind of singularity recently obtained by Dadhich and Patel (2000) are revisited. The matter content of the model is a shear-free perfect fluid with isotropic pressure and a radial heat flux. Three different exact solutions are obtained for both perfect fluid and fluid with bulk viscosity. It turns out that the cosmological rerm $\Lambda (t)$ is a decreasing function of time, which is consistent with recent observations of type Ia supernovae.

19 pages, 6 figures, submitted to Fizika B (Zagreb)