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What you're looking at

A black hole emits no light. Everything here is other light, bent by its gravity.

The picture

The shadow — the black disk. Not the event horizon itself: it's the silhouette of all the light the hole swallows, about 2.6× wider than the horizon. Any ray aimed within the critical impact parameter $b = 3\sqrt{3}\,M \approx 5.2\,M$ falls in and never returns.

The photon ring — the razor-thin bright rim hugging the shadow. Light that whipped around the photon sphere ($r = 3M$) one or more times before escaping, piling up right at the edge. It sits just outside the shadow — nothing escapes from within.

Gravitational lensing — the smeared, warped stars. Mass bends light, so the background sky is distorted and you can even see around the far side of the hole.

The accretion disk — the glowing gas (switch it on in Modules). It spirals inward and stops at the ISCO ($6M$), the innermost stable orbit — that's the disk's sharp inner edge.

The arcs over and under the hole — the disk's far side: its top face is lensed up over the hole and its underside beneath it. Tilt the disk to 90° (edge-on) for the iconic line-plus-two-crescents look.

One side brighter (Doppler beaming) — the part of the disk rotating toward you is relativistically boosted, so it blazes while the receding side dims.

Reddening (redshift) — light climbing out of the gravity well loses energy and shifts red; deeper in, time itself runs slow (watch $d\tau/dt$ in the readout).

Key radii (in $M = GM/c^2$)

• $2M$ — event horizon, the point of no return.
• $3M$ — photon sphere, where light can orbit.
• $6M$ — ISCO, the disk's inner edge.
• $3\sqrt{3}\,M \approx 5.2\,M$ — the shadow's edge, what you actually see.

Why every black hole looks the same here

The bent-light image is scale-invariant — a stellar-mass hole and a billion-sun one are identical in these units. Mass only sets the real size and clock: pick a preset (Sgr A*, M87*) to read the horizon in km and the orbital period.

Controls

Drag orbits around the hole · Shift+drag looks around · ⌥/Alt+drag moves the hole · scroll zooms. The three tabs tune the physics, the disk, and rendering quality.