Magnetic fields around black holes

The electromagnetic field near a rotating black hole is being explored in educational style here. By employing analytic solutions for electrovacuum fields, 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 structure of magnetic lines and we also propose 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 the electromagnetic origin are considered as a possible source of high-speed outflows emerging from numerous nuclei of galaxies where black holes reside.