Black holes are objects in space that are so massive or so condensed that even light can't escape them because the escape velocity from the gravity, within a radius known as the event horizon, is greater than lightspeed. Blackholes are the remnants of large stars though black holes may form in other ways as well. Since not even light can escape from a black hole, they can not be detected directly, but they can be detected by their effects on their surroundings. For instance, stars and other luminous objects may orbit around black holes. A star must be at least three solar masses for a black hole to form. Some scientists fear that human beings could create a black hole in a particle accelerator and destroy the Earth.  Present day partile accelerators will not produce stronger collisions than happen naturally through cosmic ray collisions. What about the future?
- Black Holes Tall Grande Venti
- Mysteries of Deep Space: Black Holes This video deals with Neutron Stars and Black holes.
- Violent Universe: Inside a Black Hole
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