@inproceedings{felix2009a,
title={A rigorous treatment of energy extraction from a rotating black hole},
author={Felix Finster, Niky Kamran, Joel Smoller, and Shing-Tung Yau},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191224204223101365146},
booktitle={Communications in Mathematical Physics},
volume={287},
number={3},
pages={829-847},
year={2009},
}

Felix Finster, Niky Kamran, Joel Smoller, and Shing-Tung Yau. A rigorous treatment of energy extraction from a rotating black hole. 2009. Vol. 287. In Communications in Mathematical Physics. pp.829-847. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191224204223101365146.