Mystery #3Tier 3space / gravity

What is a black hole?

Out in space lurk objects with gravity so strong that not even light, the fastest thing there is, can escape them. They're completely black and invisible. What on Earth (or off it) is a black hole?

The first real image of a black hole (in galaxy M87), a dark centre ringed by glowing gas. — Photo: Event Horizon Telescope Collaboration · CC BY 4.0 · via Wikimedia Commons

Your guess

What's your hunch about what makes a black hole so 'black' that not even light escapes?

There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.

Make a guess to unlock the hints and the answer.