Black Hole Black Hole, theoretical object of extreme density and with a gravitational field so strong that nothing, including electromagnetic radiation, can escape from it. It therefore appears totally black. In 1994 astronomers using the Hubble Space Telescope found the first convincing evidence that a black hole exists. They found that an object of 2.5 billion to 3.5 billion solar masses must be present at the center of the galaxy M87. According to general relativity, gravitation severely modifies space and time near a black hole.
Time slows down relative to that of distant observers and inside the black hole stops completely.
Black holes may form from burnt-out stars. As nuclear fuels are exhausted in the core of a star, the pressure associated with their heat no longer resists gravitational contraction of the core. If the core mass exceeds about 1.7 solar masses, collapse to a black hole follows. English physicist Stephen Hawking has suggested that many black holes may have formed in the early universe. They could compose a significant fraction of the total mass of the universe.