What is an Event Horizon?

Answer 1

For a Black Hole, it is the distance from the Black Hole, less than which, nothing can escape from the Black Hole - not even light.

Answer 2

A black hole is a super dense object that has an intense gravitational pull. There are two parts to a black hole, a singularity and a event horizon. If you were to take a slice of a black hole right through its center
The event horizon is where the force of gravity becomes so strong that even light is pulled into the black hole. Although the event horizon is part of a black hole, it is not a tangible object. If you were to fall into a black hole, it would be impossible for you to know when you hit the event horizon. For a mathematical derivation of the radius of a event horizon see below.

The singularity is not really a tangible object either. According to the General Theory of Relativity the Singularity is a point of infinite space time curvature. This means that the force of gravity has become infinitely strong at the center of a black hole. Everything that falls into a black hole by passing the event horizon, including light, will eventually reach the singularity of a black hole. Before something reaches the singularity it is torn apart by intense gravitational forces. Even the atoms themselves are torn apart by the gravitational forces.

Answer 3

It's the "black" in Black hole. Let me explain...

The answer has to do with escape velocity--the speed at which an object must travel in order to escape the gravitational pull of another object. Here on Earth, the escape velocity is around 11.2 kilometers per second, while the surface gravity is about 9.8 meters per second squared (that means you have an additional 9.8 meters of speed added per second as you fall). That means that in order to escape from the Earth's gravitational pull, you have to be able to move at 11.2 kilometers per second or better, or the earth will just pull you right back down again. The further you get away from the earth, the lower the escape velocity, until eventually, if you had somewhere to stand (and a space suit of course) you could jump free of the earth's gravity.

Since Mass and Gravity are intimately entwined together, you can easily deduce that as mass goes up, gravity goes up--and therefore the escape velocity goes up.

When an object becomes really dense, it's surface gravity goes up, even though it may remain the same mass.

When a star goes supernova, the incredible pressure at the core squeezes the material there so hard that it can start what is called gravitational collapse--the radius is shrinking, making the surface gravity more intense, which causes faster shrinking, etc. When an object reaches this critical type of collapse, it can't be stopped until it has shrunk to a point where it's density is infinite. As you can imagine, with infinite density some wild things happen to surface gravity. In fact, we aren't really sure what can happen on the surace of a black hole, because the mega-intense gravity seems to break down physics--the acceleration experienced there is faster than the speed of light, which means all the rules are broken.

This also means that there is an area, a sphere around the black hole, where the escape velocity is faster than light. As you go further from the black hole, the escape velocity decreases, just as with the earth. Eventually you reach a point where the Escape velocity is the same as the speed of light. Any closer, and not even light can escape the awesome gravity.

This area is the event Horizon.

Since no light can escape from closer in, it makes the area in space around the black hole seem, well...black.

I hope that helps!

Answer 4

It's the point at which the escape velocity of the black hole exceeds the speed of light. This means that beyond this point, light can't get out so nothing can be seen. No events are visible past this 'horizon'.

Answer 5

An event horizon is the point at which there is no return. It is often referred to as the PNR. In philosphical terms, it is the point at which free will succumbs to fate and no matter what we do, we cannot forestall or change the inevitable outcome. In astronomical terms, it is the point at which a single force, be it gravity, magnetism, or other forces, act on a body with such singularity that nothing can alter their course or prevent their collision with the attracting particles.

Answer 6

It is a membrane that will allow information or matter to travel only one way through it.
A classic example is a black hole.