Luminosity vs. temperature of the deep isotherm from numerical calculation. Note that regions of positive slope in Fig. 3 correspond to zero slope here, implying the radiative‐convective boundary jumps to a depth at which the slope is again negative. The calculation is for ﹩M=M_{\mathrm{J}\,}﹩ but can be extended to other masses using ﹩L\propto M﹩. The lines represent core entropies ﹩Sm_{p}/ k_{\mathrm{B}\,}=6,\ldots ,10﹩, from bottom to top.