The active mass density in Einstein's theory of gravitation in the analog of Poisson's equation in a local inertial system is proportional to ρ+3p/c². Here ρ is the density of energy and p its pressure for a perfect fluid. By using exact solutions of Einstein's field equations in the static case we study whether the pressure term contributes towards the mass.
No takes yet. Share an insight, caveat, or question.
Ehlers et al. (2005) studied this question.