The merger of two black holes is like a dance that ends in a powerful burst — a gravitational wave. This wave carries the imprint of how spacetime is curved around the objects. If the geometry differed from what we're used to, as if a ball rolled not on a flat floor but on wavy linoleum, the signal would be different.
The authors of the study took fresh data from the GWTC-4 catalog, a list of reliably detected gravitational signals. They looked for traces of two specific distortions, denoted as α₁₃ and ε₃. These parameters act like tuning knobs: if they are not zero, spacetime behaves in a non-Einsteinian way.
The result is several times more precise than the previous analysis from three years ago. No hints of "wrong" geometry were found. This is not just a confirmation of general relativity, but also an important step: the more events we study, the more confidently we can say that black holes are indeed described by the Kerr solution, a rotating funnel without the slightest flaw.
The most sensitive gravitational detector, LIGO, picks up mirror displacements a thousand times smaller than the size of a proton: that's like measuring the distance to the nearest star with the precision of a human hair's width.
In Carl Sagan's novel "Contact," an alien signal comes through a wormhole — an exotic solution to Einstein's equations that hasn't been confirmed yet, but studies like this one are precisely what look for the slightest deviations from the familiar geometry.