Example of an expansion curve, which is the expansion velocity of a shell as a function of the galactocentric radius. This curve is drawn for the shell number 1 and the gravitational potential of a de Vaucouleurs sphere (Sérsic sphere with index 4). The baryonic mass of the sphere is 10¹¹M_⊙, and it has the effective radius of 5 kpc. The curve asymptotically reaches the value given by Eq. (10) indicated by the dashed line.