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In globular clusters, blue straggler stars are heavier than the average star,so dynamical friction strongly affects them. The radial distribution of BSS,normalized to a reference population, appears bimodal in a fraction of GalacticGCs, with a density peak in the core, a prominent zone of avoidance atintermediate radii, and again higher density in the outskirts. The zone ofavoidance appears to be located at larger radii the more relaxed the hostcluster, acting as a sort of dynamical clock. We use a new method to computethe evolution of the BSS radial distribution under dynamical friction anddiffusion. We evolve our BSS in the mean cluster potential under dynamicalfriction plus a random fluctuating force, solving the Langevin equation withthe Mannella quasi symplectic scheme. This amounts to a new simulation methodwhich is much faster and simpler than direct N-body codes but retains theirmain feature: diffusion powered by strong, if infrequent, kicks. We compute theradial distribution of initially unsegregated BSS normalized to a referencepopulation as a function of time. We trace the evolution of its minimum,corresponding to the zone of avoidance. We compare the evolution under kicksextracted from a Gaussian distribution to that obtained using a Holtsmarkdistribution. The latter is a fat tailed distribution which correctly modelsthe effects of close gravitational encounters. We find that the zone ofavoidance moves outwards over time, as expected based on observations, onlywhen using the Holtsmark distribution. Thus the correct representation of nearencounters is crucial to reproduce the dynamics of the system. We confirm andextend earlier results that showed how the dynamical clock indicator dependsboth on dynamical friction and effective diffusion powered by dynamicalencounters.

Taking apart the dynamical clock. Fat-tailed dynamical kicks shape the blue-straggler star bimodality