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According to Einstein’s general theory of relativity, a black hole in space is a place where the gravity well is so great that a gravitational time dilation has occurred. This causes time to stop. This causes an event horizon into which objects can fall or be pulled, but those objects will never reappear. They are referred to as black because they do not reflect anything that hits them. They absorb all light. Analysis has shown that a black hole does posses a temperature and Hawking radiation.
Although it is invisible, a black hole in space can be observed through its interaction with other matter. One can be inferred by tracking the movement of a group of stars that orbit a region in space which looks empty. Also, one can see gas falling into a relatively small black hole, from a companion star. This gas spirals inward, heating up to very high temperatures and emitting large amounts of radiation that can be detected from Earth bound and Earth-orbiting telescopes. Such observations have resulted in the scientific consensus that black holes exist in our universe.
The existence of a black hole in space was first postulated in 1783. 1915 saw the release of Einstein’s theory of general relativity, but it was not until a few years later that Karl Schwarzchild found a solution that the existence of a black hole was possible. His solution is called the Schwarzchild radius. It is used to define the radius of the event horizon of a non rotating black hole.
Some scientists, and many sci-fi fanatics, believe that if you could find a way to connect black holes you could travel across space quickly and efficiently. Others believe that creating a black hole in an enclosed area would allow you to create a spacecraft engine that would never fail and launch our race into interstellar travel.
There are good articles about black holes here and here. WE have a great article here on Universe Today about the proposed ”black hole drive”. Astronomy Cast offers a good episode about stars forming in and around a black hole.