Black holes are quite legitimate and in fact very boss indeed. A black hole is formed when a big 'ol star in space undergoes a process called gravitational collapse, in which most or all of its mass is compressed into a very, very small area of space, causing infinite spacetime curvature!!! :worked_till_5am:

This means that nothing, not even light can escape from the border. And although we apparently know so much about them, nobody has ever actually observed a black hole. The theory of black holes possibly existing has been debated since the 1700's, when scientist John Michell published a paper that brought about the essential idea of the black hole, predicting that an object with a radius 500 times larger than the sun would have an escape velocity of the speed of light, and thus be invisible. Although theory died in the 1900's when we learned more about optic waves, the black hole was essentially created.

However in all this time the most brilliant men on the planet have still not been able to explain the phenomenon completely. Today there is almost a universal agreement that they exist, however nobody is sure of there exact nature, an perhaps never will be.

New modernists, most notably Stephen Hawking, believe that material which falls into a black hole may actually appear somewhere else in the universe, as in the case of a wormhole.