Nonlinear effects in black hole ringdown

Understand

We report evidence for nonlinear modes in the ringdown stage of the gravitational waveform produced by the merger of two comparable-mass black holes.

• We consider both the coalescence of black hole binaries in quasicircular orbits and high-energy, head-on black hole collisions.
• The presence of nonlinear modes in the numerical simulations confirms that general-relativistic nonlinearities are important and must be considered in gravitational-wave data analysis.