Stochastic motion, t → L_t(t), of a retrograde test star of mass μ_t = μ_⋆ for different initial conditions. The trajectory of the star is described by the Langevin Eq. (64), with the Langevin coefficients h and g obtained in Fig. 12. Because these coefficients tend to 0 for low enough angular momentum (| L_t | ≲ 2.7 × 10³), retrograde test stars cannot diffuse closer to the BH. This quenching of the resonant diffusion in the inner regions of the system is associated with the Schwarzschild barrier and is illustrated with the grey region.