Black Holes

The Schwarzschild radius

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Schwarzschild radius $r_s = 2GM/c^2$: about 3 km per solar mass.
• Inside the event horizon, nothing can escape.
• Far away, a black hole’s gravity is the same as any equal mass.

Steps

1. No escape
2. How big would the horizon be?
3. Scaling up
4. Would the Earth fall in?
5. Spaghettification
6. A surprisingly thin giant