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Black hole event horizon
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The surface beyond which nothing escapes.
The boundary r = 2GM/c² beyond which no signal can escape to outside observers. Falling in takes finite proper time, but outside observers see the infall freeze.
Crossing the horizon of a large black hole feels unremarkable.
Tidal forces differ with mass.
In more detail
The event horizon of a black hole is the boundary beyond which nothing can escape. At the Schwarzschild radius, the escape velocity equals the speed of light.
Real-world uses
- Event horizons are studied through their gravitational effects on nearby matter.
- Imaging projects have captured shadows of black hole horizons.
- Astronomers use the event horizon to explain why black holes appear black, since no light escapes from inside.
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Frequently asked questions
Can anything cross the horizon from inside?
No. Once inside, all paths lead to the singularity.
What is the event horizon telescope?
An array of radio telescopes that imaged the shadow of a black hole in 2019.
Can I see the event horizon?
Not directly. Astronomers infer it from the motion of nearby matter and from images of the glowing gas around it.
Related topics in Relativity
Einstein field equations · Geodesics · Schwarzschild metric · Hawking radiation · Gravitational waves detection · Frame dragging