Magnetic fields around black holes

Mutual interaction between electromagnetic and gravitational fields can be treated in the framework of the general theory of relativity. This poses a difficult problem but different approximations can be introduced in order to grasp interesting effects and to describe mechanisms which govern astronomical objects. The electromagnetic field near a rotating black hole is explored here. By employing an analytic solution for the weak electromagnetic field in vacuum, we plot the surfaces of constant flux and we show how the field is dragged around the black hole by purely geometrical effects of the strong gravitational field. We visualize the complicated structure of magnetic lines and we also mention possible astrophysical applications of more realistic situations involving the presence of plasma. The entangled and twisted field lines result in reconnection processes which accelerate the particles injected into the vicinity of the black hole. Such acceleration mechanisms of electromagnetic origin are considered as a possible source of high-speed plasma jets emerging from numerous nuclei of galaxies where black holes reside.