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Researchers have found the first evidence that ‘ringing’ vibrations are produced by colliding black holes. Newly merged black holes are lopsided, but quickly settle into the lowest-energy shape, a sphere. In the same way that a bell rings with specific frequencies determined by its shape, the stabilising black hole ‘rings down’, and radiates gravitational waves with frequencies that are determined by its mass and spin. A reanalysis of data from the largest black-hole merger ever detected, in 2019, indicates that it produced a black hole 250 times the mass of the Sun — much more massive than the original analysis suggested.
