What Is the Edge of a Black Hole?

The edge of a hole is not really a barrier. It's just where you fall in. The subtle point also is that you can't measure the event horizon. Technically, to calculate where the event horizon is, you need to know what happens to every particle that comes near it. Then you find sort of like the surface in which if a particle passed through it, nothing ever escaped. We did take a picture of black hole, and that does give us clues about the size of the event Horizon. But check out a whole episode about the black hole image for details about that.