A region of spacetime where gravity is so strong that nothing, not even light, can escape once it crosses the event horizon. Black holes form when massive stars collapse or through other extreme gravitational processes.
The term was popularized by physicist John Wheeler in 1967, though the concept dates to 1783 when John Michell proposed 'dark stars.' Wheeler's vivid phrase replaced earlier terms like 'gravitationally completely collapsed object' and captured the public imagination.
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