The SXS Collaboration's third catalog of binary black hole simulations

TL;DR

The paper presents a substantial expansion and refinement of the SXS binary black hole waveform catalog, increasing simulations from 2,018 to 3,756 and enhancing coverage of mass ratios, spins, and eccentric configurations using the Spectral Einstein Code (SpEC). It introduces memory and center-of-mass corrections, refined eccentricity handling, and a memory-corrected waveform pipeline, while implementing PBandJ to better handle junk radiation and AMR-driven convergence. The work demonstrates that spectral methods provide a dramatic efficiency advantage over finite-difference schemes and underscores the catalog’s readiness for current detectors and ongoing development toward next-generation observatories. A new data-archiving and access framework (including versioning and the sxs Python package) enables reproducible, scalable, and user-friendly distribution of this large, complex dataset. Together, these advances expand the practical utility of numerical relativity waveforms for waveform modeling, detector analysis, and future gravitational-wave astronomy.

Abstract

We present a major update to the Simulating eXtreme Spacetimes (SXS) Collaboration's catalog of binary black hole simulations. Using highly efficient spectral methods implemented in the Spectral Einstein Code (SpEC), we have nearly doubled the total number of binary configurations from 2,018 to 3,756. The catalog now densely covers the parameter space with precessing simulations up to mass ratio $q=8$ and dimensionless spins up to $|\vecχ|\le0.8$ with near-zero eccentricity. The catalog also includes some simulations at higher mass ratios with moderate spin and more than 250 eccentric simulations. We have also deprecated and rerun some simulations from our previous catalog (e.g., simulations run with a much older version of SpEC or that had anomalously high errors in the waveform). The median waveform difference (which is similar to the mismatch) between resolutions over the simulations in the catalog is $4\times10^{-4}$. The simulations have a median of 22 orbits, while the longest simulation has 148 orbits. We have corrected each waveform in the catalog to be in the binary's center-of-mass frame and exhibit gravitational-wave memory. We estimate the total CPU cost of all simulations in the catalog to be 480,000,000 core-hours. We find that using spectral methods for binary black hole simulations is over 1,000 times more efficient than much shorter finite-difference simulations of comparable accuracy. The full catalog is publicly available through the sxs Python package and at https://data.black-holes.org .

Figures (11)

• Figure 1: An overview of some of the most extreme systems in the updated catalog. a) SXS:BBH:2621, a very long, 147-orbit simulation viewed from the emission direction $(\theta, \phi) = (0.4\pi, 0.1\pi)$ with polarization $\psi=0.2\pi$. The non-zero value of the strain to the right of $t-t_{\mathrm{peak}}=0$ is due to gravitational wave memory that is included in this updated catalog. b) Blue: eccentric system SXS:BBH:2607 ($e_{\text{ref}}\approx 0.31$), viewed from $(\theta, \phi, \psi) = (0.3\pi, 0.5\pi, 0)$. The faint gray trace is a circular system SXS:BBH:1153 with the same mass ratio ($q=1$), time-shifted to approximately agree in orbit-averaged frequency at $t_{\text{ref}}$ of the eccentric waveform. Note the asymmetry, higher amplitude, and faster merger time of the eccentric system. Gravitational wave memory is again indicated by the nonzero value of the strain after ringdown. c) Blue: Mass-ratio $q=20$ system SXS:BBH:2516. The faint gray trace is a $q=1$ reference system SXS:BBH:4434. The horizontal axis is scaled with the symmetric mass ratio $\nu$ so that the radiation-reaction timescale is the same horizontal distance on the plot for both waveforms. Note the smaller amplitude and the much longer inspiral time of the high mass-ratio system.
• Figure 2: Distribution of reference mass ratios $q$ and spins $\chi$ in the catalog. Each panel shows a projection of the 7-dimensional space. Each point is one simulation. We plot the effective spin $\chi_\mathrm{eff}$ [a combination of spins that has a strong effect on the phasing of the gravitational waves; defined in Eq. (\ref{['eq:chieff']})] and the magnitudes of the spins in the orbital plane. Blue circles correspond to simulations that were released as part of the 2019 catalog, while orange diamonds correspond to simulations new in this release. Darker regions are more densely covered. Deprecated simulations are omitted.
• Figure 3: The number of orbits (top axis) and number of cycles (bottom axis) of the $\ell = m = 2$ GWs from the start of the simulation until the formation of a common apparent horizon for the simulations in the catalog, as determined by the coordinate trajectories of the black holes. Bin edges are multiples of 5 orbits and 10 cycles. Deprecated simulations are omitted.
• Figure 4: The reference dimensionless orbital angular frequency $M\Omega_{\mathrm{orb}}$ for the simulations in the catalog. The top axis is the frequency of the $(2,2)$ mode at the reference time for a binary with a total mass of $50\mathrm{M_{\odot}}$. Only simulations with a reference eccentricity $<10^{-2}$ are shown. Deprecated simulations are omitted.
• Figure 5: The number of simulations at different reference eccentricities $e_{\mathrm{ref}}$ in the catalog. The main population shows simulations using eccentricity reduction, while we have also completed several campaigns targeted at high $e_{\mathrm{ref}}$, yielding the tail. Deprecated simulations are omitted.