Black Holes: Light's Hidden States ✎ express
Black holes aren't faceless devourers. Sometimes they behave like water: they can 'freeze' or 'boil', changing their internal state. Scientists described this by modeling light near a black hole as a gas. This gave rise to a generalized formula for entropy (a measure of disorder), building on the ideas of Bekenstein and Hawking. The twist: this disorder is proportional to the hole's area, not its volume — the exact opposite of what we see in a cup of coffee or a cloud of steam.
The key is the light ring, formed by spacetime curvature. Its properties — rotation speed, beam divergence — sensitively mirror the temperature and pressure of the black hole. By watching the ring, you can literally see the hole undergoing its transformations.
A black hole's entropy — its measure of disorder — grows with surface area, not volume. It's as if a room seemed messier because of the size of its walls, not what's inside.
The famous glowing ring from 'Interstellar' is exactly the light ring that gives away a black hole's secrets.