High-accuracy numerical relativity simulations confirm that overtones are essential for modeling binary black hole ringdowns and reveal the presence of previously unidentified second-order quasinormal modes, validating perturbation theory as a good approximation for describing much of the ringdown.
This study confirms the presence of an overtone in the GW150914 black hole ringdown signal by addressing data analysis systematics that led to conflicting conclusions in previous studies.
Data conditioning techniques like downsampling, filtering, and data segment duration selection, while useful for computational efficiency, can significantly alter posterior distributions in black hole ringdown analyses if not carefully applied, potentially leading to systematic errors and skewed tests of general relativity.