Abstract
Spherically symmetric perfect fluids are studied under the restriction of shear‐free motion. All solutions of the field equations are found by solving a single second order nonlinear equation containing an arbitrary function. It is shown that this arbitrary function is a geometric invariant, E, which measures the gravitational field energy, and it is shown that E=const generates all the homogeneous density solutions. An improved proof is given for the nonexistence of any one‐parameter equation of state. A number of exact solutions are presented and discussed.

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