When two black holes spiral around each other and merge, they send ripples across the universe — gravitational waves. These waves carry the imprint of exactly how the objects moved before the collision. From the shape of this 'dance,' you can tell how closely the objects resemble perfect black holes.
Every black hole, like a spinning top, has mass and spin. But it also has subtler properties — how its matter is distributed and how it is 'flattened' by rotation. These properties are called moments. If an object is a true black hole, all its moments are uniquely determined by mass and spin. If it's something else, the moments can differ.
In the new study, scientists took data from the recent event GW241011. They compared how the two merging objects behaved with what theory predicts for black holes. Special attention was paid to two moments — the quadrupole and the octupole. The first is related to oblateness, the second to a finer asymmetry.
No deviations were found. This means the objects behaved like true black holes. And for the first time, they managed to constrain the octupole moment — no one had measured it before. Now we have another tool to check whether we are really seeing black holes, not something exotic.
as written by the authors arXiv:2604.09828
All multipole moments of a Kerr black hole are uniquely determined by its mass and spin. Gravitational wave observations can test this prediction by measuring spin-induced multipole moments imprinted on the inspiral phase of compact binary mergers. In this Letter, we show that the recently reported compact binary coalescence GW241011 enables a simultaneous test of deviations in the spin-induced quadrupole and octupole moments of the binary components from their black hole values. We find no evidence for deviations from the Kerr prediction and place the first constraints on spin-induced octupole moments of the compact binary. This approach complements tests of the Kerr nature of compact binary merger remnants based on quasinormal mode measurements in the ringdown phase.
Gravitational waves from black hole mergers are so weak that LIGO and Virgo detectors pick up vibrations thousands of times smaller than the size of a proton.
In the movie 'Interstellar,' the black hole Gargantua is depicted with high scientific accuracy: its appearance was calculated using equations similar to those tested in this work.