on space and time scales characterized by mean free path and mean collision time.

A relativistic second-order theory was found by Israel [@Is76] and developed by Israel and Stewart [@IsSt76], Hiscock and Lindblom [HiLi89]{} and Hiscock and Salmonson [@HiSa91] into what is called “transient” or “extended” irreversible thermodynamics. In this model deviations from equilibrium (bulk stress, heat flow and shear stress) are treated as independent dynamical variables, leading to a total of 14 dynamical fluid variables to be determined. For general reviews on causal thermodynamics and its role in relativity see [@Ma95].

Causal bulk viscous thermodynamics has been extensively used for describing the dynamics and evolution of the early Universe or in an astrophysical context. But due to the complicated character of the evolution equations, very few exact cosmological solutions of the gravitational field equations are known in the framework of the full causal theory. For a homogeneous Universe filled with a full causal viscous fluid source obeying the relation $\xi \sim \rho ^{1/2}$, with $\rho $ the energy density of the cosmological fluid, exact general solutions of the field equations have been obtained in [@ChJa97; @MaHa99a; @MaHa99b; @MaHa00a; @MaTr97]. It has also been proposed that causal bulk viscous thermodynamics 