Schwarzschild Radius
The physical radius defining the event horizon of a non-rotating, spherically symmetric black hole of mass M.
Governing formula
R_s = 2 G M / c² ≈ 2.95 km × (M / M_☉)
SI unit
Meters or Kilometers
In depth
Derived by Karl Schwarzschild in 1916. If any object of mass M is compressed smaller than its Schwarzschild radius R_s, its escape velocity exceeds c and it collapses into a black hole.
Examples in the real world
The Sun's Schwarzschild radius equal to ~3.0 km, and Earth's equal to ~8.9 millimeters.