Physical model
- Light paths: null geodesics of the Schwarzschild metric, or the Kerr metric once the hole spins, integrated for every pixel, every frame.
- Your view: the aberration seen by an observer hovering at a fixed distance. With spin, that observer is carried around just enough to have no angular momentum.
- Color and brightness: Doppler shift, gravitational redshift and beaming applied to blackbody light. A frequency shift of g turns a temperature T into gT.
- The disk: gas on circular orbits at the correct orbital speed, from the innermost stable orbit (3 rs without spin, under 1 rs at high spin) outward.
- Hot clumps: each one moves at the orbital speed for its radius, so the inside of a clump outruns the outside and it shears into a spiral arc.
Simplified
- The disk’s temperature is scaled into visible light. Real disks are much hotter and glow in ultraviolet or X-rays. Its profile uses the non-spinning formula.
- The disk’s thickness is a smooth glow, and its fine turbulence is a texture rather than a fluid simulation.
- When you point at the image, the panel flattens spinning-hole rays onto one plane.
- The time light takes to cross the scene is ignored.
Scale: rs is the event horizon’s radius. It is about 30 km for a black hole of 10 suns, and about 130 au for M87*.