The question why and how things fall down was first triggered and answered by Galileo and Newton. However, the formulation of the General Theory of Relativity by Albert Einstein early this century introduced a new perspective for the mysterious force, gravity.
Though it is known according to Newtonian physics that gravitational attraction is a function of mass (law of universal attraction), general relativity presented a fascinating view for the effect of mass on space-time, the 4-dimensional universe that we live in. A number of scientific discoveries came to reinforce general relativity, in particular the discovery of the gravitational shift, and the deflection of light due to massive celestial objects.
Then, one thought about the question: what if we have an object massive enough that light cannot escape its attraction? That was the black hole. Since their discovery, black holes have created a great interest for mathematicians and astrophysicists, as well as science fiction writers! This esoteric object is actually a "deceased" star. However, there are certain conditions that lead to the formation of black holes.
Work done by Schwarzchlid, Wheeler, Penrose, Hawking, and Thorne contributed to our understanding of black holes, and classifying their different types. Not only that, mathematical work provided other theoretical objects that are close to black holes, such as: white holes, and wormholes. These models contributed to rise of science fiction novels that dealt with space travel, such as Contact, by Carl Sagan. Yet, it seems so far that going through a black hole will not be an interesting experience!
Though theoretical, hypothetical, mathematical,
black holes are one of the alive examples for human curiosity...the uncountably
infinite human curiosity!