Maximum compactness of static stars when the lapse is tied to the isotropic conformal factor, N = 2/ψ − 1
In isotropic coordinates the Schwarzschild metric satisfies N = 2/ψ − 1 for every mass, so if the lapse is a function of the isotropic conformal factor alone, vacuum general relativity fixes that function (in areal coordinates the same argument gives a different closure, Jacobson 2007: the choice of the isotropic varia...