GW 190412 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 12 April 2019. In April 2020, it was announced as the first time a collision of a pair of very differently sized black holes has been detected. As a result of this asymmetry, the signal included two measurable harmonics with frequencies approximately a factor 1.5 (a perfect fifth) apart.