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Black holes were theoretically established in 1915, shortly after Albert Einstein published his theory of General Relativity. Since then, observations have confirmed black holes as actual astrophysical objects. In this Insight we publish ten long- and short-format pieces (in the “Reviews & Perspectives” and “Views & Comments” tabs, respectively) discussing key aspects of black holes, from their masses, to their spins, to the ways in which they impact their surroundings and are studied. This collection also showcases some of the black hole-related content that Nature Astronomy has published since our launch (in the “Primary research” and “Further reading” tabs). Also, please view our previous collection of landmark black hole discoveries published in Nature and other Springer Nature journals.
Current black hole spin measurements, in X-rays, radio and gravitational waves, are already constraining models for the growth of black holes, the dynamics of stellar core-collapse and the physics of relativistic jet production.
Supermassive black holes are fed through galaxy interactions and mergers, chaotic cold accretion in galaxy clusters and secular processes that may include stellar bars. Observations constraining these mechanisms at different scales are reviewed.
KAGRA is a new gravitational wave detector being built in Japan. Unlike LIGO/Virgo, it will operate at cryogenic temperatures with sapphire mirrors. KAGRA will help improve the localization of gravitational wave detections and determination of the source parameters.
Examining and comparing many of the definitions of a black hole, it is concluded that the profusion of different definitions is a virtue that makes the investigation of black holes possible and fruitful in many different kinds of problems.