Physics Lab
Calculators and small simulations. Type a mass below to see how small a black hole's radius can get.
Schwarzschild radius
Enter the mass of an object in solar masses to estimate the radius of its event horizon in kilometers.
Schwarzschild radius: 2.95 km
For comparison, Earth's radius is ~6,371 km.
Black hole visualization
A simplified view of a black hole: event horizon, accretion disk, and inner glow. Drag to rotate; the view auto-rotates slowly.
Light-year distances
A light-year is the distance light travels in one year, about 9.46 × 10¹² km. Even nearby stars are many light-years away.
Distance to Proxima Centauri (~4.24 ly): 40,113,368,000,000 km
For comparison, Earth-Sun distance (1 AU) is ~150 million km. Proxima Centauri is tens of thousands of times farther.
Orbital period
Estimate the orbital period of a small body around a Sun-like star using a circular orbit, then see a simple top-down sketch of that orbit.
Orbital period: 365.3 days
Earth's orbital period is ~365 days at 1 AU around the Sun.
Escape velocity
The minimum speed needed to escape a body's gravity from a given distance: v = √(2GM/r). Default values show Earth's escape velocity (~11.2 km/s).
Escape velocity: 11.18 km/s
Earth's escape velocity is ~11.2 km/s. For comparison, solar escape from 1 AU is ~42 km/s.
Gravitational lensing
When a massive object (lens) lies between us and a distant source, light bends. The Einstein radius is the characteristic angular scale of the lensed images. Distances in megaparsecs (Mpc).
Einstein radius: 63.813 arcsec
Typical galaxy-galaxy lensing: ~1 arcsec. Source must be farther than the lens.