  We consider accretion of charged test matter by rotating, magnetic black
holes and discuss a number of aspects in which the interaction of the angular
momentum contained in the electromagnetic field and the spin of the hole plays
a fundamental role. First, we argue that such a black hole tends to lose its
angular momentum by accreting charges while remaining globally neutral. Then,
we show that accretion can happen in a superradiant manner via an enhanced
Penrose process. In particular, we find that the regions from which energy and
angular momentum can be extracted contain the axis of rotation and, in some
cases, consist of floating bubbles disconnected from the black hole itself.
Finally, we address the question of whether extremal dyonic rotating black
holes can be overcharged or overspun via accretion of arbitrary matter, and
prove that this can not happen if the null-energy condition holds. We conclude
by discussing some future research directions.
