Astronomy Question of the Week: How is a black hole discovered?

Black holes are astrophysical objects with an almost unbelievably high mass per unit volume. They are so heavy that they are able to powerfully warp the space around them. Within a certain distance from the black hole ? the ‘event horizon’ ? this warping of space is so strong that absolutely no light or any [...]

Full story at http://spacefellowship.com/2009/12/07/astronomy-question-of-the-week-how-is-a-black-hole-discovered/