Multipole moments on the common horizon in a binary-black-hole simulation

We construct the covariantly defined multipole moments on common horizon of an equal-mass, non-spinning, quasicircular binary-black-hole system. see a strong correlation between these and gravitational waveform. find that are well described by fundamental quasinormal modes at sufficiently late times. For each moment, least two different $\ell$ detectable in best model. These models provide faithful estimates true mass spin remnant black hole. also show including overtones, $\ell=m=2$ moment admits excellent quasinormal-mode description all times after merger. This demonstrates perhaps surprising power perturbation theory near