Hi everyone, first time poster here... I'm learning General Relativity from some old course notes I got from my friend and am just wondering if anyone can suggest a good source which would have a detailed description (calculations etc) of the Penrose process and how it relates to Black Hole thermodynamics. All I have is "Penrose process-energy extraction from spinning BH." It seems obvious that by finding an E<0 trajectory in the ergoregion and shooting a particle along this trajectory opposite the spin direction of the BH's one could in principle extract energy because conservation of angular momentum would "slow down" the spinning BH. This doesn't seem so surprising, so why the big deal? Perhaps I am missing something. Any suggestions or sources would be very appreciated-thanks!