You're listening to the faint whisper of stars, and nearby someone keeps moving a chair. In gravitational wave telescopes, that role is played by scattered light: it reflects off trembling surfaces and creates false signals. The peculiarity of such noise is that it appears as repeating arcs on a time-frequency map, like a series of arches receding into the distance.
The new method, f-cluster, proposed for the Japanese detector KAGRA, captures the periodicity of these arcs. It scans the spectrogram, a kind of "musical notation" of mirror vibrations, and highlights regions with excess power. The algorithm then estimates how often the arcs appear and calculates the vibration frequency of the object scattering the light. No guesses about the source's nature are needed.
Over April 2025, f-cluster detected scattering at a frequency of 0.432 Hz — roughly one oscillation every two and a half seconds. Moreover, the number of such events turned out to be closely linked to ground shaking in the 0.3–1.0 Hz range: the Pearson correlation coefficient reached 0.82. This means that seismic data can predict when noise will spoil observations, allowing researchers to prepare for data cleaning in advance.
Now physicists have a tool that not only catches parasitic light but also hints at where to look for its source. And that's a step toward making the universe's whisper more audible.
A frequency of 0.432 Hz is close to the rhythm of calm human breathing — about one breath every 2.3 seconds.
In Carl Sagan's novel "Contact," a false signal from space turned out to be a reflection from an airplane — terrestrial noise can masquerade as the voices of alien civilizations.