http://www.sciencemag.org/news/2020/09/middleweight-black-holes-finally-found-they-pose-puzzle

The merger of middleweight black holes churned up gravitational waves that were detected on Earth.

Far away in the depths of space, two black holes spiral toward each other and merge. Powerful gravitational waves from that dance of death race across the cosmos until their ripples reach three giant detectors on Earth: two with the U.S.-based Laser Interferometer Gravitational-wave Observatory (LIGO) and Europe’s Virgo detector in Italy.