GW 190412 was a
gravitational wave (GW) signal observed by the
LIGO and
Virgo detectors on 12 April 2019.[1][2] In April 2020, it was announced as the first time a collision of a pair of very differently sized
black holes has been detected.[3] As a result of this asymmetry, the signal included two measurable
harmonics with frequencies approximately a factor 1.5 (a
perfect fifth) apart.[2][4]
The collision took place 2.4 billion
light-years away.[3] The heavier of the black holes had a mass of 29.7 solar masses, and the lighter one around 8.4 solar masses.[3] The difference in mass meant that the secondary
harmonic in the signal was strong enough to be detected, allowing researchers to perform a test of
general relativity and determine that the larger black hole was spinning.[3]