A study reports that the steady “background hum” of gravitational waves produced by many unresolved compact binaries in the Milky Way carries information about the Galaxy’s rotation. Rather than only arising from rare, dramatic events such as black hole mergers, gravitational waves also exist as a persistent signal from millions of pairs of dead stars—mostly white dwarfs in the context of the Milky Way. Individually, these sources are too weak to detect directly, but collectively they form a continuous noise-like spectrum. The researchers find that this combined signal includes a subtle “fingerprint” related to the Milky Way’s spin. They warn that future space-based observatories, such as ESA’s LISA mission, that analyze and subtract this gravitational-wave background could arrive at a slightly incorrect interpretation of the Milky Way’s properties if the rotational imprint is ignored. The work emphasizes that accurate modeling of the gravitational-wave foreground is necessary to extract reliable astrophysical information from the data.