Black Hole Image Simulator
How this works: the tool remaps your uploaded image using an educational gravitational-lensing model. Changing mass and angular momentum alters how strongly light paths bend. It is a teaching visualization—not a telescope pipeline.
What you are seeing
The simulator places a non-rotating (Schwarzschild) black hole between the camera and your image, then works out where each pixel's light must have come from. Rays that pass close to the black hole are bent strongly, so the background is stretched into a bright Einstein ring. Rays that come too close fall in, leaving the dark disc of the black hole's shadow. The thin rings just outside the shadow are light that looped partly around the black hole before reaching the camera.
- Mass (M) changes how strongly light bends. Bigger values give a bigger shadow and a wider ring.
- Starting photon angular momentum (L) controls the first light ray in the sweep the simulator traces, which changes how the innermost rings are drawn.
- Pictures with a bright horizontal band, like the Milky Way, show the ring most clearly.
How the simulation works
Light follows paths called null geodesics. The simulator solves the photon equations of motion in the Schwarzschild metric for a range of rays, records how far each ray is deflected, and uses that mapping to warp every pixel of your image. This is backwards ray tracing, the same idea used for the black hole in Interstellar, simplified so it runs in a few seconds. The full derivation and code are in Chapter 3: Ray Tracing in the Schwarzschild Geometry.
It is a teaching tool, not a telescope pipeline. Real black holes spin and are surrounded by glowing gas, which makes their images asymmetric (compare Kerr vs Schwarzschild black holes).