How a black hole forms
- A giant star runs out of fuelMany times heavier than the Sun
- Its core collapsesGravity crushes it inward
- An event horizon formsThe point of no return
- Nothing comes back outNot matter, not light
Event horizon
Not a surface, just the boundary past which escape is impossible.
Milestones
| Year | Discovery |
|---|---|
| 1915 | Einstein's general relativity describes gravity as curved space-time |
| 2015 | LIGO detects gravitational waves from two black holes merging |
| 2019 | First image of a black hole, in galaxy M87 |
| 2022 | Image of Sagittarius A*, the black hole at our galaxy's center |
Sagittarius A* holds about 4 million times the Sun's mass.
Gravity bends time
Clocks run slower near mass
Time passes a bit slower closer to Earth
GPS must correct for it
Without the fix, positions would drift miles a day
Extreme near a black hole
Time nearly stops at the horizon, as seen from far away
Squeeze Earth
It would become a black hole under an inch across
Sources: NASA; Event Horizon Telescope; LIGO
Remember
Black holes show that gravity bends both space and time, and your phone's GPS proves it every day.
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Answer key
- What can escape from inside a black hole's event horizon?NothingNothing escapes once inside the horizon.
- What usually forms a black hole?The collapse of a giant starMassive stars collapse at the end of their lives.
- When was the first image of a black hole released?2019The Event Horizon Telescope image of M87 came out in 2019.
- What did LIGO detect in 2015?Gravitational wavesRipples in space-time from merging black holes.
- Why does GPS need relativity corrections?Satellite clocks run at a different rateGravity and speed change how fast the satellite clocks tick.