Sizheng Ma

GW240925 and GW250207 are two loud gravitational-wave signals from binary black hole coalescences observed with network signal-to-noise ratios ∼ 32 and ∼ 69 , respectively, by the LIGO Hanford-LIGO Livingston-Virgo network. Gravitational-wave signals from coalescing binaries have characteristic phase and amplitude evolution predicted by general relativity. These signal waveforms, together with measured instrumental calibration uncertainties, are used to infer source parameters. However, for sufficiently loud detections, it is possible to constrain the calibration of the detectors directly using the signals themselves. We present the first informative astrophysical measurements of gravitational-wave detector calibration. For GW240925, we verify the inference of Hanford calibration from the astrophysical signal through cross-checks with known calibration errors obtained from measurements. At the time of GW250207, the Hanford detector was not fully stabilized, leading to elevated calibration uncertainties; thus, astrophysical calibration is essential to obtain accurate data and to enable source localization. These well-localized, high signal-to-noise observations have the potential to offer precise measurements of source properties, stringent tests of general relativity, and informative dark siren measurements, provided that calibration uncertainties are properly incorporated. As detector sensitivity improves, astrophysical calibration will become an increasingly valuable complement to calibration measurements. Obtaining accurate calibration will be essential for precision gravitational-wave science.

Gravity in nonlinear and dynamical regimes underpins spectacular astrophysical phenomena and observable consequences, from the early Universe to black hole collisions. In these extreme environments, "inverse energy cascades"-mediated by nonlinear interactions-may help explain the near scale invariance of cosmic structure and the simplicity of gravitational waves from binary black hole mergers. Yet the presence, characteristics, and generality of such interactions in full general relativity remain largely unexplored. Here we show that two types of nonlinear interactions-a four-mode and a three-mode interaction-emerge in the fully nonlinear regime and can indeed channel inverse energy cascades by inducing resonant and antidamping (transient) nonlinear instabilities. We further demonstrate a "laminar" to "turbulent" transition for the largest-possible angular structure in general relativity, whereas finer structures remain persistently turbulent. Our results reveal the impact and generality of these nonlinear interactions (instabilities), which can be key to understanding observations ranging from cosmological to kilometer scales. We anticipate that our Letter will shed new light on nonlinear gravitational phenomena and their consequences, such as constructing gravitational-wave templates and testing general relativity in the most extreme regime. Moreover, our Letter is a starting point for addressing nonlinear gravitational interactions using ideas and methods inspired by fluid dynamics.

We present a major update to the Simulating eXtreme Spacetimes (SXSs) Collaboration’s catalog of binary black hole (BBH) simulations. Using highly efficient spectral methods implemented in the Spectral Einstein Code (SpEC), we have nearly doubled the total number of binary configurations from 2018 to 3756. The catalog now more densely covers the parameter space with precessing simulations up to mass ratio q = 8 and dimensionless spins up to | χ → | ⩽ 0.8 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 × 10 − 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 BBH simulations is over 1000 times more efficient than previously published finite-difference simulations. The full catalog is publicly available through the sxs Python package and at https://data.black-holes.org .