Radial distance evolution test. Comparing the N-body simulation (black dots) and the point-mass integration (solid red line). The dashed line represents the integration without the bulge mentioned in Sect. 2.5. The lines at the bottom represent the difference between the red line and the dashed line, while the solid black line represents the difference between the red line and the orbit computed considering the dynamical friction (see text for details and Sect. 2.5).