Hi everybody, When I have a perfect fluid within a constant gravitational field g, the pressure at depth z simply reads P=\rho g z, where \rho is the fluid density (incompresible). If now my g is still constant, but my fluid is relativistic. Not because it's moving (everything is still) but because it is hot with k_B T \sim mc^2. What happens to P = \rho g z ? Thanks!