Understanding black hole radius
Calculate the Schwarzschild radius for a black hole of a chosen mass.
The idea behind it
The event horizon is a boundary in spacetime, not a material surface. For a non-rotating, uncharged black hole, its radius grows linearly with mass.
The relationship to remember
rₛ = 2GM/c² ≈ 2.95334 km × 10 solar masses = 29.53 km.
Make your own discovery
Double the mass. Unlike the radius of an ordinary star, this horizon radius also doubles.
Try the interactive lab ↗What this model leaves out
The Schwarzschild solution: no rotation or electric charge. The glowing ring is an explanatory illustration, not an image prediction. It is not the size of an observed black hole shadow.
Check your understanding
Would a black hole with the Sun’s mass pull Earth in?
At Earth’s distance it would have the same gravitational pull as the Sun, neglecting other differences. Earth’s orbit would not suddenly collapse.
Is the bright ring the event horizon?
No. Glowing material and bent light can appear around a black hole; the horizon itself does not emit light that escapes.
Continue with the formula reference or test yourself in space practice.