horizon

What you’re looking at

• The black circle is the shadow of the event horizon. It looks about 2.6 times bigger than the horizon itself, because gravity bends light from behind it into your eyes.
• The arc over the top is the back of the disk. Its light has been bent up and over the hole to reach you, which is why the disk seems to wrap around it.
• One side is brighter. The disk spins at a good fraction of light speed. The side coming toward you gets boosted, the side moving away is dimmed (Doppler beaming).
• The thin inner ring is light that looped around the hole, maybe more than once, before escaping. It sits on the photon sphere at 1.5 times the horizon radius.
• The stars near the edge are smeared and doubled. That’s gravitational lensing: you’re seeing the same stars along more than one path.

Distances are in r_s, the radius of the event horizon. Light paths follow the real Schwarzschild equations. The disk is a thin, idealised one.