A Black hole is a region from space from which nothing, not even light can escape from it. The Black Hole in the middle of the Milky is more than 4 million solar masses.
Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun. The term black hole can also be called Neutron Star. Karl Schwarzschild was credited with being the astronomer who developed the concept of the black holes.

http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/Daniel_Barnes/Page2.htm http://en.wikipedia.org/wiki/Black_hole
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A black hole is an extremely dense celestial body which is believed to exist in our universe. THe gravitational force of a Black Hole is so strong that light can enter it but not escape.

The Black Hole Concept was developed by a German Astronomer in 1916, named Karl Schwarzschild. He based his studies on Albert Einstein's general theory of gravity.

The point when no matter can escape the gravitational force of a black hole is called the Event Horizon. You can only see a black hole when light is entering it, not any other time.

Black Holes are still a mystery to mankind which is why we don't know all the facts about Black Holes.

Black Holes are also called Neutron Stars.