Nonrotating and nonexpanding perfect fluids
It is fairly well-known that nonstationary spacetimes exist which are filled with a nonrotating and nonexpanding perfect fluid, provided the fluid does not admit an equation of state. It is less well-known that the same is true when an equation of state does exist. Even when all possible invariants of a perfect fluid solution depend on a single spatial coordinate only, the corresponding solutions need not be stationary.
scientific article; zbMATH DE number 4032565