Modern astronomy has produced a theory about the life of stars in which the fate of a star crucially depends on how massive it is. Lighter stars might end as red dwarfs, and heavier stars as enormously dense but tiny neutron stars. The heaviest stars collapse in upon themselves, creating black holes. Black holes are called black because the gravitational force associated with them is so strong that no light can escape. The infinite gravitational attraction at the edge of an event horizon such as a black hole not only warps space but also warps time for the hypothetical observer near the black hole.

See also ASTROPHYSICS; COSMOLOGY, PHYSICAL ASPECTS;