Plasma injection and outflow formation in Kerr black holes

We discuss the role plasma injection plays in the formation of outflows in Kerr spacetime. Using a model for the double flow established in the polar region of a rotating black hole, we study the interplay between the different processes that can power the outflow. In particular, we find two types of flows with distinct properties that depend on the rate at which energy is deposited in the magnetosphere. We discuss the implications of this result for gamma ray bursts outflows.