Thermal index of npeγ matter as a function of baryon density n_b for different temperatures and a fixed proton fraction of Y_p = 0.2. Solid lines show the total thermal index of asymmetric matter, Equation (24). Dashed lines display the nuclear thermal index, Equation (29), while the dashed–dotted line represents the lepton contribution. The two dotted lines indicate the thermal index of an ideal relativistic and nonrelativistic gas, corresponding to Γ_th = 4/3 and 5/3, respectively.