The boundary of a black hole is said to be surrounded by event horizon - the point of no return! What is its significance in terms of general relativity?
closed as too broad by called2voyage♦ Mar 10 '14 at 18:38
Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
It is exactly the point of no return for light. In other words, it is the point (actually more like a sphere) in which the escape velocity from the Black Hole gravity reaches $c$.
What I mean to say is, how are the characteristics of event horizon related to Space-Time?
Formally, an event horizon is the boundary of a region of spacetime that's not in the causal past of future null infinity. In other words, the boundary of a region from which even idealized light rays cannot escape to infinity. Whenever the event horizon is smooth, it is also null hypersurface--i.e., the direction perpendicular to it is a light ray.
Because the event horizon is defined in terms of the infinite future, the definition is very non-local, and one would need to know the entire future history to be sure where the event horizon is. As such, it is only one of a half-dozen different types of horizons used to study black holes.
Though the event-horizon itself is a three-dimensional hypersurface in spacetime, it can also be viewed as an evolving two-dimensional membrane made of a viscuous electrically conducting fluid with finite temperature and entropy but zero thermal conductivity.