What boundary around a black hole is the point of no return for light and matter?

The event horizon is the boundary around a black hole that marks the point of no return for light and matter.

It is not a solid surface. Instead, it is a boundary in spacetime: once an object crosses it, every future path that remains possible leads inward, so no signal can reach a distant observer. Light emitted from inside cannot escape, which is why the black hole itself appears dark.

The event horizon should not be confused with the accretion disk, the hot, glowing material orbiting outside the hole. It is also different from the photon sphere, where light can orbit under particular conditions, and from the ergosphere surrounding a rotating black hole, where spacetime is dragged around by the hole’s spin. In a rotating black hole, the event horizon is generally oblate rather than perfectly spherical.

For a sufficiently large black hole, a freely falling observer might cross the horizon without noticing a locally dramatic event. The danger comes from the global structure of spacetime: after crossing, escape to the outside is no longer possible.