Anatomy of the lensed image
Seen nearly edge-on (80°), the same flat disk appears below the shadow in front and arched above it behind — light bent by gravity. The side spinning toward you looks brighter and whiter.
Shadow is not pure black
Faint warm glow inside, brightest along the lower-left edge where hot gas skims the horizon.
Razor photon ring
A razor-thin ring where light circles the hole before escaping — brightest where motion blueshifts it.
Relativistic beaming
Gas coming toward you is beamed and looks whiter; gas moving away looks dimmer and redder.
Lensed above and below
Front of the disk below the shadow; far side bent over the top; a second, lensed image tucked underneath.
Frame-dragged shear
Spin drags space itself, shearing the disk into streaks.
Per fragment Schwarzschild null integration
d2p dlambda2 = -3/2 h2 p / r5, Binet u'' = -u + 3/2 rs u2. Velocity-Verlet with angular sweep, bendC continuous via sub-Verlet.