The Invisible Boundary

The event horizon is not a physical surface. You cannot touch it, stand on it, or see it. It is a mathematical boundary — the radius at which the escape velocity equals the speed of light. Since nothing can travel faster than light, anything that crosses this boundary can never return.

The size of the event horizon is set by the Schwarzschild radius, calculated as 2GM/c², where G is the gravitational constant, M is the mass, and c is the speed of light. The Sun's Schwarzschild radius is about 3 kilometers.