In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

These objects are thought to provide power to blazars. The rotating versions of these bodies described by the Kerr metric are surrounded by ergospheres from which energy can be gained in the Penrose process, and they can be described by mass, charge, and angular momentum according to the [*] no-hair theorem. They aren't neutron stars, but after exploding in supernovae, stars that have overcome the electron degeneracy pressure of the Chandrasekhar limit can form these objects. Featuring an event horizon at the Schwarzchild radius surrounding a gravitational singularity, for 10 points, name these astronomical objects so massive that no light can escape them.
Science