Near a bathtub drain the pull grows so strong that a floating toy can't paddle away. A black hole is gravity's ultimate drain: past a certain edge, not even light is fast enough to swim back out.
A place gravity won't let light leave
A black hole is a region where gravity is so strong that nothing — not even light — can escape. Many form when a very massive star exhausts its fuel and collapses under its own gravity. The mass is concentrated so densely that space and time are extremely warped around it.
The event horizon is the boundary of no return: cross it and no signal can get back out. It is not a solid surface but a point beyond which escape would require moving faster than light.
In 2019 the Event Horizon Telescope imaged the shadow of the supermassive black hole in galaxy M87 — direct evidence they exist.
- Recall that we see objects by the light they emit or reflect.
- Note that no light escapes past the event horizon.
- Explain why a black hole appears black.
What you should see: Since no light can escape the event horizon, none reaches us — so the region appears black against the background.