Two drums: one swallows the beat silently, the other ricochets it back. That's how an ordinary black hole and its hypothetical twin — a black mirror — are built. The first has an event horizon, a point of no return. The second has a reflective surface: nothing falls in, everything is thrown back.

When a star spirals toward such an object, it punches spacetime, emitting gravitational waves. For a black hole, the sound quickly fades, swallowed by the horizon. For a black mirror, the waves bounce back and forth, creating a long echo with a distinct frequency spectrum — quasinormal modes. But the pace of infall also differs: a slow mirror decelerates the falling body by reflecting energy; a fast one accelerates it, because it suppresses the effect that, in ordinary holes, feeds orbital motion. Future observatories like LISA will notice this difference in rhythm.