The Lazarus Project. II. Spacelike extraction with the quasi-Kinnersley tetrad

TL;DR

This paper introduces a new method using the quasi-Kinnersley frame to improve gravitational wave extraction from numerical black hole simulations, especially in near-Kerr spacetimes, enhancing robustness and accuracy.

Contribution

It develops a novel spacelike extraction technique employing the quasi-Kinnersley tetrad, valid in nonlinear regimes, to better analyze late-time black hole spacetimes and extract gravitational radiation.

Findings

Successfully tested on Bowen-York data for spinning black holes

Provides a more robust wave extraction method

Quantifies tetrad-related errors in previous Lazarus results

Abstract

The Lazarus project was designed to make the most of limited 3D binary black-hole simulations, through the identification of perturbations at late times, and subsequent evolution of the Weyl scalar $\Psi_4$ via the Teukolsky formulation. Here we report on new developments, employing the concept of the ``quasi-Kinnersley'' (transverse) frame, valid in the full nonlinear regime, to analyze late-time numerical spacetimes that should differ only slightly from Kerr. This allows us to extract the essential information about the background Kerr solution, and through this, to identify the radiation present. We explicitly test this procedure with full numerical evolutions of Bowen-York data for single spinning black holes, head-on and orbiting black holes near the ISCO regime. These techniques can be compared with previous Lazarus results, providing a measure of the numerical-tetrad errors intrinsic to the method, and give as a by-product a more robust wave extraction method for numerical relativity.