Three.js Scroll Black Hole — Accretion Disk Dive

The Three.js Scroll Black Hole Approach snippet drops the camera toward a black hole wrapped in a 5,200-particle accretion disk — inner particles white-hot and orbiting fast, outer ones rust-red and slow, a photon ring hugging the shadow — while scroll accelerates the fall, multiplies the disk's apparent speed as a time-dilation metaphor, and creeps the camera's field of view wider for that stretched, pulled-in horizon feeling. Where the planet approach brakes into orbit, this one accelerates past the point of no return.

Keplerian orbits from a power law

Each disk particle stores polar parameters — radius, phase, vertical tilt, and an angular velocity ω = 14 / r^1.5 — the same r^−3/2 falloff as real Keplerian orbits, so the inner disk visibly laps the outer disk exactly the way accretion physics demands. Positions are computed fresh every frame from parameters plus time (the stateless design shared with the tornado vortex), which keeps the scrub exact at any scroll speed. Radius distribution uses pow(rand, 1.6) to crowd particles toward the inner edge where the action is.

Temperature as vertex color

Real accretion disks are hottest where orbital energy dissipates fastest — the inner edge. Each particle's color is assigned once at build time by double-lerping white-hot → orange → rust across normalized radius, stored in a color BufferAttribute with vertexColors: true and AdditiveBlending. Where particles crowd near the inner edge, additive blending stacks their brightness into a glowing band — the blackbody gradient emerges from geometry density rather than any texture.

The shadow is just an unlit sphere

The black hole itself is the cheapest mesh in the scene: a MeshBasicMaterial sphere in pure black, which ignores lighting by definition. Against the additive disk and starfield, an object that reflects *nothing* reads as a hole in space — no shader needed. The photon ring is a thin warm torus riding just outside the shadow, pulsing subtly on clock time and brightening plus swelling with approach, standing in for the lensed light band made famous by the EHT image and *Interstellar*.

Time dilation as a speed multiplier

The scroll's signature move: disk time advances as t × (1 + p^2.4 × 11), so at full approach the disk spins eleven times faster than at the start, and the HUD reports the multiplier as TIME DILATION n×. It is a metaphor rather than relativity — a real infalling observer would see the opposite — but it compresses "the universe speeds up as you fall" into one legible, scrubbable number. Because the multiplier applies to *clock* time inside the stateless position math, scrolling back down smoothly decelerates the disk with zero state to unwind.

FOV creep and lensing hints

Nearing the horizon, camera.fov interpolates from 60° to 84° with updateProjectionMatrix() each frame — a dolly-zoom-like stretch that makes the shadow balloon in the final stretch of scroll. The starfield counter-rotates slightly against the camera swing as a cheap suggestion of gravitational lensing, and the disk tilts more edge-on as the camera dives toward the orbital plane, trading the top-down spiral view for the *Interstellar* silhouette. For the gentler cousins of this scene, see the galaxy formation and starfield warp snippets.