Some Properties of the "string Gas" with the Equation of State p = -(1)/(3) ρ

We show that the string gas — a perfect fluid with the equation of state p = -(1)/(3) ρ possesses rather interesting properties. In Friedmann universes its presence can change the observable topology of the space; in the spherically symmetric spacetimes it produces rather bizzare geometries and in a way its influence on the rotation curves mimics the dark matter effects.