The story behind this piece
Not an artist's impression: the disk in this image was ray-traced. Light was followed backwards along the exact paths photons take around a non-spinning black hole, u″ + u = 3GMu²/c², to find where it came from. A thin disk of gas orbits from the innermost stable orbit, three Schwarzschild radii, outward. Gravity bends the far side of the disk up over the shadow and down beneath it, and a fine photon ring outlines the shadow at 2.6 Schwarzschild radii. Gas moving toward us is Doppler-beamed and blazes; the receding side dims. The background stars are shifted with a simpler lensing approximation, and the warm palette is mapped from the physics rather than true colour.
