The merger of a binary black hole creates a highly distorted final black hole. The gravitational radiation emitted during this relaxation offers a unique opportunity to probe extreme gravity and its connection to black hole horizon dynamics. Using numerical relativity simulations, the authors demonstrate a correlation between observable features in gravitational waves and geometrical properties of the final black hole's dynamical apparent horizon. Specifically, they show how the line-of-sight passage of a 'cusp'-like defect on the horizon correlates with 'chirp'-like frequency peaks in the post-merger gravitational waves. These post-merger chirps are expected to be observable with increased sensitivity of LIGO, Virgo, LISA, and the Einstein Telescope.

Juan Calderon Bustillo, Christopher Evans, James A. Clark, Grace Kim, Pablo Laguna, Deirdre Shoemaker