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The accretion of a spherically symmetric, collisionless kinetic gas cloud onto a Schwarzschild black hole is analysed. Whereas previous studies havetreated this problem by specifying boundary conditions at infinity, here theproperties of the gas are given at a sphere of finite radius. The correspondingsteady-state solutions are computed using four different models with anincreasing level of sophistication, starting with the purely radial infall ofNewtonian particles and culminating with a fully general relativisticcalculation in which individual particles have angular momentum. The resultingmass accretion rates are analysed and compared with previous models, includingthe standard Bondi model for a hydrodynamic flow. We apply our models to thesupermassive black holes Sgr A* and M87*, and we discuss how their lowluminosity could be partially explained by a kinetic description involvingangular momentum. Furthermore, we get results consistent with previousmodel-dependent bounds for the accretion rate imposed by rotation measures ofthe polarised light coming from Sgr A* and with estimations of the accretionrate of M87* from the Event Horizon Telescope collaboration. Our methods andresults could serve as a first approximation for more realistic black holeaccretion models in various astrophysical scenarios in which the accretedmaterial is expected to be nearly collisionless.

Accretion of a Vlasov gas on to a black hole from a sphere of finite radius and the role of angular momentum