The gravitational wave strain emitted by a perturbed black hole (BH) ringing down is typically modeled analytically using first-order BH perturbation theory. In this Letter, we show that second-order effects are necessary for modeling ringdowns from BH merger simulations. Focusing on the strain's (ℓm)=(4,4) angular harmonic, we show the presence of a quadratic effect across a range of binary BH mass ratios that agrees with theoretical expectations. We find that the quadratic (4,4) mode's amplitude exhibits quadratic scaling with the fundamental (2,2) mode - its parent mode. The nonlinear mode's amplitude is comparable to or even larger than that of the linear (4,4) mode. Therefore, correctly modeling the ringdown of higher harmonics - improving mode mismatches by up to 2 orders of magnitude - requires the inclusion of nonlinear effects.
CITATION STYLE
Mitman, K., Lagos, M., Stein, L. C., Ma, S., Hui, L., Chen, Y., … Vu, N. L. (2023). Nonlinearities in Black Hole Ringdowns. Physical Review Letters, 130(8). https://doi.org/10.1103/PhysRevLett.130.081402
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