How a black hole forms
The short answer
Why the heaviest stars collapse, what an event horizon is, and how small the Sun would have to be squeezed to become a black hole.
0:28ScienceIntermediateblack holesstarsgravity
Chapters and transcript
- 0:00
A big star holds itself up
Gravity pulls the star inwards. Heat from nuclear fusion in its core pushes outwards, and the two stay in balance.
- 0:07
When the fuel runs out, it collapses
In stars far heavier than the Sun, the core is crushed by its own gravity and the outer layers explode.
- 0:14
Not even light can escape
The crushed core can become a black hole. Inside its event horizon, gravity is so strong that nothing, not even light, gets back out. Light passing close by is bent.
- 0:21
Squeeze the Sun to 6 km across
The Sun is about 1.4 million km wide. Packed into a ball about 6 km across, even the Sun would be a black hole, though it is not heavy enough to collapse that far on its own.