Physics

Black Hole

See a black hole the way its light does. Every pixel is a photon traced back along its bent path, so the far side of the glowing disk rises over the top and the whole sky folds round a shadow 2.6 times the size of the horizon. Then put a particle in orbit: it traces rosettes that never close, cannot circle closer than 3 rₛ, and its clock runs slow near the hole.

approaching side: brighter, bluerreceding side: dimmer, redderorbit, coloured by its clock rateNewtonphoton sphere 1.5 r_sinnermost stable orbit 3 r_s

Drag to orbit the camera, scroll to move closer or farther

Shadow radius—

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View

Camera distance r 22 rₛ

Height above the disk 8°

Accretion diskSky gridFlat space (light goes straight)Shadow guides

Numbers

Camera at r / r_s—

Camera clock √(1 − r_s/r)—

Shadow radius b_c—

Shadow across your sky—

Render resolution—

What to observe

The disk is flat, yet its far side shows above the hole and again below it: that light bent over and under the shadow to reach you. The side turning towards you is brighter and bluer.
Hide the disk and paint a target on the sky: its gold spot, straight behind the hole, shows as a ring all the way round it, an Einstein ring. Tick Flat space and the spot just hides behind a black ball of radius r_s.
A bound orbit never closes: each pass the closest point moves on, tracing a rosette. Newton's ellipse with the same start closes on itself.
Below L = √3 r_sc there is no stable orbit, so the particle plunges. Seen from far away its clock slows to a stop and it freezes at the horizon.

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