Extracting Energy and Angular Momentum from a Kerr Black Hole

Abstract

In this thesis we take a look at energy and angular momentum extraction from a rotating black hole. We start off by introducing basic concepts regarding black hole before moving on to Kerr black holes. We compute basic properties of a Kerr black hole such as its the location of its event horizon, the area of the event horizon and we introduce the ergosphere. \par Next we move on to the constituting mechanism for energy and angular momentum extraction from a Kerr black hole: the Penrose process. The basic idea of the Penrose process is that it is possible for a particle within the ergosphere to have a decay product which has a negative energy. If such a decay product falls into the black hole, it extracts energy and angular momentum from it.\par A more effective energy and angular momentum extraction mechanism is the Blandford-Znajek process. The Blandford-Znajek process is an electromagnetic process and understanding it amounts to understanding three central components of which we only discuss two in detail in this thesis. \par Firstly, we need to understand force-free electromagnetism. This can be understood as the physics explaining how the energy and angular momentum is being carried away. This force-free electromagnetism induceses a current in the plasma surrounding the black hole. This current is connected to the electromagnetic fields and carries away the energy and angular momentum. \par Secondly we will briefly take a look at the plasma surrounding the black hole. We will answer the question of how it is formed and what properties it has to satisfy. \par Lastly, we need to take a look at the mechanism explaining how energy and angular momentum is take away from the black hole. For a positive radially outflowing energy flux measured far away from the black hole, we require a negative radially inflowing energy flux near the black hole. Here we also recognise the role of the Penrose process.