Gravitational waves from a ringing black hole support the no-hair theorem
General relativity suggests the spacetime oddities can be fully described by their mass and spin
![black hole rings](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2019/09/091319_ec_blackhole_feat.jpg?fit=1028%2C579&ssl=1)
After two black holes collide and meld into one, the new black hole “rings” (illustrated), emitting gravitational waves before settling down into a quiet state.
M. Isi/MIT, NASA