A black hole is a great amount of matter packed into a very small area. For example, the image of a star, ten times the size of the sun squeezed into a sphere aptly describes it. The result is a gravitational field so strong that, even light can’t escape. Most black holes are formed of the remnants of a large star that dies in a supernova explosion.
The idea of an object in space, dense enough to prevent even light from escaping is centuries old. Einstein first predicted black holes in 1915 with his General Theory of Relativity. Karl Schwarzschild used Einstein’s General Theory of Relativity to find out what happens near a massive star that has collapsed to a single point. He found that they emit no light, but can be detected by the effect of their gravity on nearby stars.
Astronomer John Wheeler coined the term black hole in 1967. Cygnus X-1, the first object considered to be a black hole was discovered in 1964.
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