A gravitational wave observatory is like a set of microphones scattered across the Earth. When a signal arrives from space (say, from a black hole merger or a supernova explosion) each microphone hears something slightly different. Until now, it was assumed that the wave front is flat, like light from a distant searchlight. And for current detectors like LIGO and Virgo, that's true: the wave is so weak and so far away that its curvature can be neglected.
The authors built a model that describes a gravitational burst not as a plane wave but as a focused beam with transverse structure — a so-called paraxial wave packet. In the era of third-generation detectors (like the Einstein Telescope), this structure will become noticeable. It will cause a geometric phase shift — an additional rotation of the wave at the reception point, depending on how the beam passed through the detector. If this shift is ignored, you could miss a real signal or misjudge its source.
To test the idea, the researchers ran a simple experiment on simulated data. They compared two burst search methods: the standard one, which ranks events by strength, and a new one that penalizes events where signals at different detectors are geometrically inconsistent. It turned out that at a fixed false alarm rate, the new method finds 3–4 times more real signals. At the same time, for ordinary plane-wave signals, it performs no worse than the old method.
A gravitational wave from a black hole merger stretches and squeezes space by less than the diameter of a proton, and it's precisely these displacements that LIGO and Virgo detect.
In Carl Sagan's novel Contact, an alien signal contains instructions for building a machine that uses gravitational waves, but there they're for travel, not astronomy.