Could the environment around black holes amplify hidden gravitational signals?

In a modified gravity theory called dynamical Chern-Simons gravity, an oscillating shell of matter near a black hole can act like a resonant cavity, triggering runaway growth of a hidden scalar field through Mathieu instability. The amplified scalar then drives a secondary burst of gravitational waves — a delayed echo with a distinctive sideband frequency pattern. Crucially, even ultraweak couplings to beyond-standard physics could build up over time and leave detectable imprints in gravitational wave data.