Throw an object, like a ball, into space from Earth at an approximate speed of 25,000 miles per hour. The object would have enough momentum to escape Earth's gravity and reach outer space. This speed is scientifically referred to as an escape velocity and differs for all gravitational fields. The more mass a planet or star has, the stronger its gravitational field, thus the greater its escape velocity. Black holes' masses are so large that their theoretical escape velocity is greater than the speed of light, making them appear colorless or black.
Black holes form when a star at least 30 times the mass of the Sun dies and collapses under its own weight. The star then shrinks into an infinitely dense point known as a singularity. Around a singularity lies an imaginary circle referred to as the event horizon. Inside an event horizon, the concepts or conventional understandings of space and time completely break down.
A person falling into a black hole would be impossible to observe. Theoretically, if one approached a black hole, time would slow to the extent that it would take an infinite amount of time to reach. Additionally, the black hole's gravitational pull on light would make the person appear as if he or she were fading away. No one knows for sure, however, what would happen in reality.
Calculations recently made by mathematician Roger Penrose at Oxford University in England suggest that it may be possible for advanced technology to extract enough energy from a black hole to supply power to all of civilization. This would require a structure encircling a black hole with a stream of fuel fed into it. The particles in the fuel stream would be split into two fragments. One fragment would fall into the event horizon, while the other would emit a kick of pure energy supplied by the push of the first fragment.
Penrose's theory also indicates that energy could be collected from these "kicks." The energy collected this way, however, would not be unlimited. Black holes gradually reach a point at which their energy producing properties diminish.
Currently, modern technology is nowhere close to creating this type of machine. Yet, over decades of technological advancements and increases in space exploration, black holes may become a vital energy supplier.
[Source: Secrets of the Universe]