Physical radii of type 1 (blue solid line) and type 2 (red solid line) critical cores as a function of core mass. The black curve represents homogeneous spheres in virial equilibrium (zero outside pressure) with temperature corresponding to the mean temperature of the 1 M_⊙ type 1 MBES. Also plotted are the physical radii of critical isothermal cores corresponding to the mean temperature of each non-isothermal core (dashed lines; see text).