The approach to homologous expansion is shown by comparing the early-time (black lines) and late-time (red lines) 3D simulations of models B15-2 (panel a)), N20-P (panel b)), W18 (panel c)), and W20 (panel d)). The solid lines give the homology index q = ∂lnv/∂lnr, the dotted lines the ⁵⁶Ni mass fraction. Bullets mark the outer boundary of the bulk of ⁵⁶Ni containing 99% of the total ⁵⁶Ni mass.