A black hole bends the path of light itself. Rays passing far away swerve only slightly — the deflection Arthur Eddington measured at the 1919 eclipse, confirming Einstein's general relativity over Newton's.
Aim closer and the bending grows without limit. At one exact impact parameter, b = 3√3 GM/c² ≈ 2.60 Schwarzschild radii, a ray neither escapes nor falls in — it circles the hole forever on the photon sphere at r = 1.5 rₛ.
Any ray aimed inside that critical radius is swallowed. Seen from far away, that captured cone is a dark disk — the black hole's shadow — whose glowing edge the Event Horizon Telescope imaged around M87* in 2019. You are finding that edge by hand: sweep the aim until the beam just grazes the shadow.
The simulation stopped unexpectedly — the lesson continues without it. You can move on; nothing you did was wrong.