Dynamical friction for compound bodies

In the framework of the fluctuation–dissipation approach to dynamical friction, we derive an expression giving the orbital energy exchange experienced by a compound body, as it moves, interacting with a non-homogeneous discrete background. The body is assumed to be composed of particles endowed with a velocity spectrum and with a non-homogeneous spatial distribution. The Chandrasekhar formula is recovered in the limit of a point-like satellite with zero velocity dispersion and infinite temperature moving through a homogeneous infinite medium. In this same limit, but dropping the zero satellite velocity dispersion (σS) condition, the orbital energy loss is found to be smaller than in the σS=0 case by a factor of up to an order of magnitude in some situations.