Normally, by rapidly oscillating a mirror in a vacuum, you can conjure real particles from nothing: this is the dynamical Casimir effect. But near a black hole, things are different. The spacetime curvature itself stifles any attempt to create something.
As you approach the hole's edge, the local speed of light tends toward zero. To keep the mirror from outpacing light, its oscillation amplitude must shrink in proportion to the distance to the horizon — otherwise the speed limit is violated. Right at the boundary, motion nearly freezes, and the vacuum remains untouched.
Thus the black hole acts as a silent guardian: its geometry tames any mechanical vibrations, shielding the vacuum from disturbances.
An unexpected twist: the damping of particles isn't due to the quantum nature of the vacuum. It's dictated by pure geometry — to simply not outrun light, the mirror must come to a halt. Quantum laws only slightly tweak this inevitability.
The scenario recalls scenes from "Interstellar": near a black hole, time freezes, and all rhythms stop — only here it's not fiction but a calculation.