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

• Published in: arXiv.org 2021-09
• Main Authors: Gamboa, Aldo, Gabarrete, Carlos, Domínguez-Fernández, Paola, Núñez, Darío, Sarbach, Olivier
• Format: Article
• Language: English
• Subjects: Angular momentum; Astronomical models; Boundary conditions; Deposition; Elliptical galaxies; Event horizon; Luminosity; Supermassive black holes
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2107.04830

The accretion of a spherically symmetric, collisionless kinetic gas cloud on to a Schwarzschild black hole is analysed. Whereas previous studies have treated this problem by specifying boundary conditions at infinity, here the properties of the gas are given at a sphere of finite radius. The corresponding steady-state solutions are computed using four different models with an increasing level of sophistication, starting with the purely radial infall of Newtonian particles and culminating with a fully general relativistic calculation in which individual particles have angular momentum. The resulting mass accretion rates are analysed and compared with previous models, including the standard Bondi model for a hydrodynamic flow. We apply our models to the supermassive black holes Sgr A* and M87*, and we discuss how their low luminosity could be partially explained by a kinetic description involving angular momentum. Furthermore, we get results consistent with previous model-dependent bounds for the accretion rate imposed by rotation measures of the polarised light coming from Sgr A* and with estimations of the accretion rate of M87* from the Event Horizon Telescope collaboration. Our methods and results could serve as a first approximation for more realistic black hole accretion models in various astrophysical scenarios in which the accreted material is expected to be nearly collisionless.