POLAR CIRCULAR ORBITS IN THE SPACETIME OF BLACK-HOLES

The motion of test particles along circular orbits passing alternately over the north and south poles of the Kerr-Newman black hole including the presence of an external magnetic field is considered. It is shown that the bounds of existence, stability and binding for circular orbits are essentially displaced towards the event horizon with the growth of the electric charge and angular momentum of the black hole. The results of analytical and numerical analysis for particular values of the parameters of a test particle and black hole are given.