Orbital decay of satellites crossing an accretion disc

Motion of stellar-mass satellites is studied around a massive compact body which is surrounded by a gaseous slab of a stationary accretion disc. The s atellites suffer an orbital decay due to hydrodynamical interaction with th e disc medium (transitions across the disc, gap opening in the disc, densit y waves) and gravitational radiation. Arbitrary orbital eccentricities and inclinations are considered, and it is observed how the competing effects d epend on the parameters of the model, namely, the mass and compactness of t he orbiters, the osculating elements of their trajectories, and surface den sity of the disc. These effects have a visible impact on the satellites lon g-term motion, and they can produce observational consequences with respect to galactic central clusters. It is shown that the satellite-disc collisio ns do not impose serious restrictions on the results of gravitational wave experiments if the disc medium is diluted and the orbiter is compact but th ey are important in the case of environments with relatively high density. We thus concentrate on application to accretion flows in which the density is not negligible. We discuss the expected quasi-stationary structure of th e cluster that is established on sub-parsec scales within the sphere of gra vitational influence of the central object. Relevant to this region, we giv e the power-law slopes defining the radial profile of modified clusters and we show that their values are determined by satellite interaction with the accretion ow rather than their initial distribution.