Changes

===Mathematics===

===Mathematics===

There are several solutions of the Einstein field equations that are used to model black holes.  The simplest of these is the Schwarzchild metric.  From this metric, one kind calculate the Schwarzschild radius, which defines the boundary of the black hole, to be

There are several solutions of the Einstein field equations that are used to model black holes.  The simplest of these is the Schwarzchild metric.  From this metric, one kind calculate the Schwarzschild radius, which defines the boundary (event horizon) of the black hole, to be

:<math>r_s=\frac{2GM}{c^2}</math>,

:<math>r_s=\frac{2GM}{c^2}</math>,

where

where