A black hole is a region of spacetime exhibiting gravitational
acceleration so strong that nothing--no particles or even
electromagnetic radiation such as light--can escape from it.
The theory of general relativity predicts that a sufficiently
compact mass can deform spacetime to form a black hole.
The boundary of the region from which no escape is possible is
called the event horizon. Although the event horizon has an
enormous effect on the fate and circumstances of an object
crossing it, no locally detectable features appear to be
observed. In many ways, a black hole acts like an ideal black
body, as it reflects no light. Moreover, quantum field theory
in curved spacetime predicts that event horizons emit Hawking
radiation, with the same spectrum as a black body of a
temperature inversely proportional to its mass.
Black Holes -- Prediction, Properties, and Structure
Black Holes -- Formation, Evolution, and Hawking Radiation
Black Holes -- Observational Evidence
Black Holes -- Open Questions