Event Horizon Lab

A physically accurate black hole built for teaching, which runs in any browser. Every pixel traces a ray of light backwards through the curved space around a non-spinning black hole, so the dark shadow, the glowing disk seen wrapped over and under the hole, and the thin ring of trapped light all come out of the physics rather than being drawn. A probe can be dropped in to show what a distant observer sees: it slows, reddens and fades at the horizon without ever crossing it. Gravity follows general relativity; quantum mechanics is being added in stages, starting with Hawking radiation, which shows the hole glowing, heating up and evaporating.

Question

Can a black hole be taught by letting people explore one — the shadow, the light bent around it, a probe that never visibly crosses the horizon?

My role

Individual. The physics model, the ray-tracing shader and the interface.

Method

General relativity (Schwarzschild geometry) · GPU ray tracing · Numerical integration

Tools

WebGL fragment shader · JavaScript · one self-contained HTML file

Evidence

Checked against the results the physics requires: a shadow of about 2.6 Schwarzschild radii, the innermost stable orbit at 3, and a probe that fades at the horizon without crossing it; the approximations are listed in the repository.

Result

The shadow, the lensed disk and the photon ring come out of the physics; none of them is drawn.

≈2.6

Shadow radius, Schwarzschild radii

3

Innermost stable orbit, Schwarzschild radii

0

External libraries

Computes

• Light bending: each ray is integrated through the Schwarzschild geometry, producing the shadow at about 2.6 Schwarzschild radii, the lensed disk and the photon ring
• Accretion disk from the innermost stable orbit at 3 Schwarzschild radii outwards, with temperature falling as r^(−3/4), Keplerian rotation and Doppler beaming
• A probe in radial free fall that a distant observer never sees cross the horizon, while its own clock reaches it in finite time
• Tidal stretching across a 2-metre body: spaghettified at one solar mass, intact at Sagittarius A*
• Hawking radiation: the temperature, the band the glow falls in, the power, and an evaporation run from any mass down to the final burst, set against the 2.7 K cosmic background

Output

Live interactive simulation on GitHub Pages, free to use for teaching; open-source code on GitHub.

BoundaryAn educational simulation, not a research instrument: disk Doppler beaming is simplified, the probe’s redshift is taken along a single line of sight, the drawn tidal stretch is a visual scale while the tidal numbers are exact, Hawking emission counts photons only, and spinning black holes are not modelled.