The LIGO Scientific Collaboration, working with Virgo and KAGRA researchers, has demonstrated a way to use gravitational-wave signals themselves to calibrate detector performance.
Known as astrophysical calibration, the technique uses the predicted shape of loud gravitational-wave signals to identify and correct distortions in detector data. It gives researchers a backup route when a detector is operating in an unsettled state or when conventional on-site calibration measurements are incomplete.
The work is based on two loud black-hole merger signals from the fourth observing run of the LIGO-Virgo-KAGRA network. GW240925 was detected on 25 September 2024 and was produced by the merger of black holes around nine and seven times the mass of the Sun. GW250207 was detected on 7 February 2025 and involved black holes around 35 and 30 solar masses.
Both signals were recorded while the LIGO Hanford detector in Washington had calibration complications. During GW240925, a temporary calibration error was later measured and corrected, allowing the astrophysical calibration method to be checked against known detector information. During GW250207, Hanford had only recently come online and some auxiliary monitoring systems were not collecting data, making the signal-based approach central to the final analysis.
Compact binary mergers create gravitational-wave signals with a characteristic phase and amplitude evolution predicted by general relativity. By comparing the expected waveform with signals recorded across the detector network, researchers can infer how one detector’s response is distorting the data and account for that effect.
Dr Christopher Berry, of the University of Glasgow’s Institute for Gravitational Research, said: “Gravitational waves are ripples in spacetime that stretch and squeeze space. They are tiny by the time that they reach the Earth, millions of years after the events that first created them.”
Calibration quality affects the science extracted from each detection. Better correction supports more accurate estimates of black-hole masses, spins, distances, and sky locations, while reducing the risk that detector error could be mistaken for unusual physics or allowed to weaken tests of general relativity.
Cardiff University’s Professor Stephen Fairhurst, spokesperson for the LIGO Scientific Collaboration, said: “It’s remarkable that these massive cosmic events can not only be measured by our instruments but actually used to check our measurements.”
The paper, “GW240925 and GW250207: Astrophysical Calibration of Gravitational-wave Detectors”, has been accepted for publication in Physical Review Letters. The preprint is available on arXiv.
