Numerical Relativity in Gravitational-Wave Astronomy: From Waveforms to Horizons

Gravitational-wave detection and inference rely on accurate models of compact-binary signals across inspiral, merger, and ringdown. Numerical relativity (NR) provides the only first-principles solution of the fully nonlinear two-body problem in general relativity, and it plays a central role in connecting strong-field dynamics to the waveform models used in searches and parameter estimation.

In this talk, I will give a beginner-oriented overview of how NR enters the GW modeling pipeline. I will describe what NR simulations compute and how their outputs are converted into “model ingredients” used in practice: calibration of semi-analytical inspiral–merger–ringdown models, training of surrogate models, and construction of remnant fits (final mass, spin, and recoil) that control ringdown attachment and consistency tests. I also discuss promising recent developments in which Numerical Relativity is being used in new ways to shed light not only on the gravitational waves received in the weak-field regime, but also on the horizon physics in the strong-field, non-linear regime.