Imagine a force so powerful that not even light can escape its grasp. Hard to imagine? It exists in the form of a black hole. The gravitational field of a black hole can pull in light and just about anything else that makes it past its event horizon. Black holes are called such because since it can absorb visible light, its interior is rendered invisible and indistinguishable from the space around it. It can be seen depending upon the orbiting matter that is interacting with it outside its event horizon. Telescopes have detected gas spiraling in a black hole after emitting large amounts of radiation.
John Michell first came up with the idea that an object could have such a strong gravity force in 1783. Michell’s belief coincided with French physicist Pierre-Simon Laplace’s belief about such forces. Black holes theoretically work under Albert Einstein’s general theory of relativity. In other words, when a large amount of mass is present in a suitably small part of space, all paths through space warp inward toward the center of its volume, and matter and radiation cannot escape it.
There is more than one type of black hole. They are categorized as solutions to Einstein’s general theory of relativity. The simplest black hole is called the Schwarzschild black hole, named after physicist Karl Schwarzschild. These black holes have mass but neither charge nor angular momentum. In the 20th Century, the Reissner-Nordström solution was discovered. This black hole has an electrical charge. The Kerr Solution black hole rotates in space. The Kerr-Newman metric black hole has both an electrical charge and angular momentum.
Most people seem to think black hole suck in everything around it. That is not exactly true. Based on the Schwarzschild solution, it means there is no difference observable to human eyes or telescopes between a black hole and an object of the same mass once it is in the empty space outside an object. Its external gravitational field is the same as normal bodies of the same mass.
The size of a black hole can contain up to a billion solar masses. The largest known black hole measures an incredible 18 billion solar masses. Intermediate-mass black are believed to form from collisions of lower mass black holes. Stellar-mass black holes from 1.5-3.0 to 15-20 solar masses. Micro black holes have a mass less than a star. Read more about black holes at: http://www.smithsonianmag.com/