Introduction
A black hole is a region in space-time, the gravitational attraction which is so large that it can not leave even objects moving at the speed of light, including photons of light itself. The boundary of this region is called the event horizon, and its characteristic dimension - the gravitational radius. In the simplest case of a spherically symmetric black hole Schwarzschild radius is equal to it.
Theoretically, the possible existence of such regions of space-time should be of some exact solutions of Einstein's equations, the first of which was obtained by Karl Schwarzschild in 1915. The exact inventor of ...