Kerr-de Sitter spacetime, Penrose process and the generalized area theorem

Understand

We investigate various aspects of energy extraction via the Penrose process in the Kerr-de Sitter spacetime.

• We show that the increase in the value of a positive cosmological constant, $\Lambda$, always reduces the efficiency of this process.
• The Kerr-de Sitter spacetime has two ergospheres -- associated with the black hole and the cosmological event horizons.
• We prove by analysing turning points of the trajectory that the Penrose process in the cosmological ergoregion is never possible.