20 Apr 2020 — On April 12, 2019, the twin LIGO detectors and the Virgo detector observed gravitational-waves from the merger of two black holes. While nearly all previous detections originated from binary black holes with almost equal masses, this event (labeled GW190412) displayed clear signatures of an unequal mass binary. A detailed analysis of the gravitational-wave signal indicates that the two black holes had masses of about 30 and 8 times the mass of the sun. General relativity predicts that binary systems with such mass differences will introduce higher “harmonics” into the waveform, and these were in-fact observed for the first time in this event.
For more details, see the GW190412 detection page.