the sources being described by an appropriate energy-momentum tensor, and so the Principle of Superposition does not apply. This means that one cannot simply pile up masses in any given spacetime because the field equations must be solved for each and every configuration of matter proposed.(This paragraph was taken from http://news.yahoo.com/black-holes-may-su… but they deleted it from the article.......
https://en.wikipedia.org/wiki/Shell_theo…
In Einstein’s theory the gravitational field, manifest in the curvature of spacetime, is coupled to its sources by the field equations, the sources being described by an appropriate energy-momentum tensor, and so the Principle of Superposition does not apply. This means that one cannot simply pile up masses in any given spacetime because the field equations must be solved for each and every configuration of matter proposed.
(This paragraph was taken from http://news.yahoo.com/black-holes-may-su… but they deleted it from the article. Apparently somebody couldn't stand the implication of what it said.)
Source: http://www.thunderbolts.info/wp/2012/08/…
A "black hole" is a star that collapsed in on itself and became very dense. The gravity field around it is so powerful that if light passes too close to it, it is sucked in and cannot escape. It doesn't emit any light, or let us see what is behind them (because it sucks in the light and holds it there), hence the "black hole" in space.
A black hole is, to put it simply, an extremely dense object. The density of a black hole creates a huge gravitational pull that light can't even escape, such as a star collapsing in on itself.
