[Paper Review] The Fourth RIT binary black hole simulations catalog: Extension to Eccentric Orbits

James Healy, C. O. Loustó|arXiv (Cornell University)|Jan 31, 2022

Pulsars and Gravitational Waves ResearchPhysics and Astronomy102 references86 citations

TL;DR

This paper presents the fourth release of the RIT binary black hole waveform catalog, significantly expanding previous catalogs by adding 824 simulations of eccentric black hole binaries with eccentricities up to e = 1. Using high-accuracy numerical relativity simulations with the LazEv code and improved initial data (HiSpID), the catalog provides extrapolated gravitational waveforms (ℓ ≤ 4 modes of ψ4 and strain H), corrected for center-of-mass drift, and remnant properties. A key contribution is the discovery of new, simple correlations between peak radiation and remnant black hole parameters that remain valid even in the presence of eccentricity, enabling improved astrophysical modeling and parameter estimation for gravitational wave events.

ABSTRACT

This fourth release of the RIT public catalog of numerical relativity black-hole-binary waveforms \url{http://ccrg.rit.edu/~RITCatalog} consists of 1881 accurate simulations that include 446 precessing and 611 nonprecessing quasicircular/inspiraling binary systems with mass ratios $q=m_1/m_2$ in the range $1/128\leq q\leq1$ and individual spins up to $s/m^2=0.95$; and 824 in eccentric orbits in the range $0<e\leq1$. The catalog also provides initial parameters of the binary, trajectory information, peak radiation, and final remnant black hole properties. The waveforms are corrected for the center of mass drifting and are extrapolated to future null infinity. As an application of this waveform catalog we reanalyze all of the peak radiation and remnant properties to find new, simple, correlations among them, valid in the presence of eccentricity, for practical astrophysical usage.

Motivation & Objective

• To extend the RIT numerical relativity waveform catalog to include highly eccentric binary black hole systems with e > 0, filling a critical gap in existing catalogs.
• To provide accurate, extrapolated gravitational waveforms (ψ4 and strain H) for 1881 simulations, including 824 eccentric binaries, with corrections for center-of-mass drift.
• To identify and validate new, simple correlations between peak radiation and final remnant black hole properties that remain robust even in the presence of eccentricity.
• To support future gravitational wave parameter estimation and surrogate modeling by offering a comprehensive, publicly accessible dataset with high-fidelity initial and final state parameters.

Proposed method

• Simulations were performed using the LazEv code with the BSSN formalism and Carpet mesh refinement, employing high-order finite differencing and Kreiss-Oliger dissipation for stability.
• Initial data were generated using the TwoPunctures code and generalized to HiSpID for highly spinning and eccentric binaries, reducing spurious gravitational wave content.
• Eccentric orbits were produced by reducing the tangential momentum of quasi-circular initial data by a factor (1−ϵ), with eccentricity computed via d²¨d/m during evolution.
• Waveforms were extracted at finite radii and extrapolated to future null infinity using standard techniques, ensuring accurate amplitude and phase information.
• Remnant properties (mass, spin, recoil velocity) were computed via the Christodoulou formula and flux integrals of ψ4, with center-of-mass correction applied post-merger.
• Correlations between peak radiation and remnant parameters were derived using statistical fitting across the full catalog, including eccentric systems.

Experimental results

Research questions

• RQ1 How do peak gravitational wave amplitudes and energies correlate with final remnant black hole mass and spin in eccentric binary black hole systems?
• RQ2 Can simple, universal correlations between remnant and peak radiation parameters be identified that remain valid across both quasicircular and eccentric orbits?
• RQ3 What is the impact of initial eccentricity on the efficiency of energy and angular momentum radiation during black hole binary coalescence?
• RQ4 How do the new HiSpID initial data improve the accuracy and stability of long-term eccentric binary simulations compared to standard puncture data?
• RQ5 To what extent do the observed correlations in this catalog remain valid when extrapolated to astrophysically relevant eccentricities?

Key findings

• The catalog includes 1881 high-accuracy numerical relativity simulations, of which 824 are in eccentric orbits with initial eccentricities ranging from 0 < e ≤ 1.
• All waveforms are extrapolated to future null infinity and corrected for center-of-mass drift, ensuring high-fidelity amplitude and phase information for gravitational wave detection and parameter estimation.
• New, simple correlations were discovered between peak radiation (energy, linear and angular momentum flux) and final remnant black hole properties (mass, spin, recoil velocity), valid across both quasicircular and eccentric systems.
• The correlations remain robust even at high eccentricities, suggesting that remnant properties can be predicted from early-waveform features without full simulation, enabling faster parameter inference.
• The catalog provides detailed initial parameters, trajectory data, and final remnant properties, with uncertainties reported to high precision (e.g., δMIH and χIH to 5–6 decimal places), enhancing its utility for data analysis.
• The dataset is publicly accessible at http://ccrg.rit.edu/~RITCatalog and is already being used for parameter estimation in LIGO-Virgo O1/O2 events, demonstrating its practical astrophysical relevance.