Why light can't escape a black hole

The familiar picture goes like this: to escape Earth, you need a speed of about 11 kilometers per second, and the more massive the body, the more you need. It seems like a black hole's threshold is simply higher than the speed of light - and nothing travels faster than light. The answer is right, but the reason isn't: light doesn't speed up or lose a race.

The speed of light is always the same. What changes is spacetime itself: mass curves it, and a ray follows the straightest available path - much like a plane flies "straight," yet traces an arc on a map. Near the Sun, this bending is tiny, but it has been measured many times.

Near a black hole, the bending reaches its limit. Just above the horizon, a ray aimed straight up can still escape, while one sent at an angle rises, curves around, and falls back. The closer to the horizon, the narrower this escape cone becomes; at the horizon itself, it collapses. Below it, there isn't a single direction that leads away.

In 2019, the first image of the surroundings of a supermassive black hole was revealed - in the galaxy M87. The hole itself doesn't glow; the hot gas around it does. Part of the bright ring is made of rays that curved around the hole and still made it to us. The dark spot in the middle is noticeably larger than the horizon itself: rays passing nearby also bend inward.

There is a transitional band, too. Light emitted almost at the boundary still reaches us, but stretched out: its wavelength grows, and photons arrive less and less often. From the outside, a flashlight dropped in wouldn't go out all at once - it would redden and fade until it vanished completely.

Most often, the problem is the word "sucks." From far away, a black hole pulls exactly like any body with the same mass: if the Sun suddenly became a black hole, the planets' orbits wouldn't shift - it would just become dark and cold. Things become unusual only right near the horizon.