Event horizon

Definition

The event horizon is the boundary surrounding a black hole beyond which nothing, not even light, can escape. It marks the limit where gravitational pull becomes so strong that escape velocity exceeds the speed of light.

5 Must Know Facts For Your Next Test

1. The event horizon is also known as the 'point of no return' for a black hole.
2. Its radius is directly proportional to the mass of the black hole and can be calculated using $R_s = \frac{2GM}{c^2}$, where $R_s$ is the Schwarzschild radius.
3. Beyond this boundary, all paths bring objects closer to the singularity at the center of the black hole.
4. Observers outside the event horizon can never see anything crossing it due to extreme time dilation effects.
5. The concept of an event horizon arises from Einstein's General Theory of Relativity.

Review Questions

• What happens to objects that cross the event horizon?
• How does the radius of an event horizon relate to a black hole's mass?
• Why can't we observe events occurring inside an event horizon?

Related terms

Schwarzschild Radius:

The radius defining the size of the event horizon for a non-rotating black hole.

Singularity: A point at which density becomes infinite and volume goes to zero inside a black hole.

Escape Velocity:

The minimum speed needed for an object to break free from another object's gravitational influence.