This book focuses on one mechanism in black hole physics which has proven to be universal, multifaceted and with a rich phenomenology: rotational superradiance. This is an energy extraction process, whereby black holes can deposit their rotational energy in their surroundings, leading to Penrose processes, black-hole bombs, and even Hawking radiation. Black holes are key players in star formation mechanisms and as engines to some of the most violent events in our universe. Their simplicity and compactness make them perfect laboratories, ideally suited to probe new fields or modifications to the theory of gravity. Thus, black holes can also be used to probe some of the most important open problems in physics, including the nature of dark matter or the strong CP problem in particle physics.

This second edition stresses the role of ergoregions in superradiance, and completes its catalogue of energy-extraction processes. It presents a unified description of instabilities of spinning black holes in the presence of massive fields. Finally, it covers the first experimental observation of superradiance, and reviews the state-of-the-art in the searches for new light fields in the universe using superradiance as a mechanism.

Richard Brito is a Marie Curie Fellow at “Sapienza” University in Rome. His research focuses on black-hole and gravitational-wave physics with an emphasis on the potential to use gravitational waves to solve fundamental problems in physics. His PhD thesis was awarded the “Professor Abreu Faro” Prize in 2016 for the best thesis completed between 2015 and 2016 at Instituto Superior Técnico in the subjects of electronics, computer science, physics and mathematics. In 2018 he was awarded the “Alberto Prize”, a prize awarded by the Portuguese Society for Relativity and Gravitation to promising young researchers.

Vitor Cardoso is Full Professor of Physics at Técnico (Lisbon), where he leads the Gravity Group. His research focuses on strong-gravity problems, with implications for gravitational-wave and black-hole physics, high-energy and particle physics. He is the author of over 200 scientific papers. He is an Outstanding Referee for the American Physical Society. His research was recognized by the European Research Council with two prestigious ERC Grants. In 2015 he was awarded the “Ordem de Sant’Iago da Espada” title, for scientific achievements, by the President of the Portuguese Republic. Prof. Cardoso is currently the Chair of GWverse, an international Consortium of over 30 countries and hundreds of scientists, which aims to study black-holes, gravitational waves and fundamental physics. He is a founding member of the Portuguese Society for Relativity and Gravitation.

Paolo Pani is Associate Professor of Theoretical Physics at “Sapienza” University of Rome and Junior Fellow of the School for Advanced Study at “Sapienza”. He is a former Marie-Curie Intra-European Fellow and is now the Principal Investigator of the ERC DarkGRA project "Unveiling the dark universe with gravitational waves". He has been awarded with the SIGRAV Prize and with the Outstanding Referee award from the American Physics Society. He is author of 100+ scientific papers on black-hole, neutron-star, and gravitational-wave physics and their connections to fundamental questions in physics.