Brightness features in the disk around HD 163296 move faster than Keplerian rotation. If they were physical structures — clumps, vortices, embedded planets — they would orbit at the local Keplerian speed. They don't. They move too fast.
Uyama, Currie, and collaborators (arXiv:2602.20346) show that the features are not orbiting structures. They are shadows — cast by the inner disk onto the outer disk. The inner disk, warped or tilted by a few degrees, blocks starlight from reaching specific parts of the outer disk. As the inner disk rotates (at its own faster Keplerian speed), the shadow sweeps across the outer disk at a rate determined by the inner disk's orbital period, not the outer disk's. The shadow moves faster than any physical structure at the outer disk's radius could.
The outer disk is the screen. The inner disk is the projector. What looks like a moving object is a moving illumination pattern. No matter is transported. No physical structure orbits at the observed speed. The speed measurement is real — something IS moving that fast — but the thing moving is light's absence, not mass.
This is a general diagnostic. When a feature in an extended system moves faster than the local speed limit for physical structures, it is likely a projected pattern rather than a material object. The distinction between shadow and substance is detectable from dynamics alone. Substance respects local speed limits. Shadows don't.
MWC 480 shows the same phenomenon. Two disks, same mechanism, same diagnostic. The inner regions of protoplanetary disks routinely cast shadows on their outer regions, and the shadows masquerade as physical features until their super-Keplerian motion gives them away.