Nelson Christensen

Two sensitive microphones are listening to the Universe. One hears a low hum, the other hears almost nothing. It's not a malfunction: it's about how they are oriented. Gravitational-wave observatories like LIGO don't just catch loud bursts from black hole mergers.

For a whole year, LIGO, Virgo, and KAGRA listened to the trembling of spacetime. Thousands of mergers of black holes and neutron stars left clear signatures. But hidden among them was another signal — a barely audible whisper.