  A distorted black hole radiates gravitational waves in order to settle down
in one of the geometries permitted by the no-hair theorem. During that
relaxation phase, a characteristic damped ringing is generated. It can be
theoretically constructed from the black hole quasinormal frequencies (which
govern its oscillating behavior and its decay) and from the associated
excitation factors (which determine intrinsically its amplitude) by carefully
taking into account the source of the distortion. Here, by considering the
Schwarzschild black hole in the framework of massive gravity, we show that the
excitation factors have an unexpected strong resonant behavior leading to giant
ringings which are, moreover, slowly decaying. Such extraordinary black hole
ringings could be observed by the next generations of gravitational wave
detectors and allow us to test the various massive gravity theories or their
absence could be used to impose strong constraints on the graviton mass.
