Eigenvalues of the fundamental mode in the slow case (dashed) and masses of SDs with B_core = 10⁵⁵, close to the maximum, M_max ∼ 0.996 M_⊙ (solid), plotted as functions of the central energy density, ϵ₀. The zero of ω² coincides with the maximum mass, and it turns negative at higher densities. Since ϵ₀ remains almost constant in the range displayed in the figure, we show its tiny change with respect to the central density, ϵ_0  bare, of a pure QS that has the same B_core.