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What is a black hole, and what would happen if you fell in? (for a curious adult who has not studied physics). Cover, in this order: What is a black hole?; How can gravity be strong enough to trap light?; How does a black hole form?; What is the event horizon?; What happens if you fall into a black hole?; If nothing escapes, how do we see black holes?; Do black holes really suck everything in?; Can a black hole die? — page 1: What a black hole is
Mass pulls on things, as you know. Now cram a huge amount of mass into a tiny space. That squeezing is the seed of a black hole.
Normally you can escape gravity by moving fast enough. Near a black hole, the pull is so strong that even light, the fastest thing, gets dragged back.
Normally a rocket escapes gravity by going fast enough. Near a black hole the pull is so strong that even light cannot get away and is dragged back.
We see things when light reaches our eyes. If no light can escape a region, we see nothing there, so it looks black: a patch of total darkness.
The name misleads. It's not a hole or a drain in space. It's a region where lots of mass is concentrated, and gravity there traps light.
So a black hole is gravity winning completely: mass squeezed so tight that nothing nearby, not even light, can get back out.