Abbott, R.Abbott, T. D.Abraham, SAcernese, FAckley, KAdams, CAdhikari, Rana XAdya, VaishaliAffeldt, CAgathos, M.Agatsuma, K.Altin, PaulEichholz, JohannesForsyth, PerryGrace, BenjaminHolland, NathanKijbunchoo, NutsineeMcClelland, DavidMcManus, DavidMcRae, TerryScott, Susan M.Shaddock, DanielSlagmolen, BramToyra, DanielWade, AndrewWard, RobertWette, KarlYap, Min Jet2022-03-022022-03-022470-0010http://hdl.handle.net/1885/261609We report the observation of gravitational waves from a binary-black-hole coalescence during the first two weeks of LIGO's and Virgo's third observing run. The signal was recorded on April 12, 2019 at 05∶30∶44 UTC with a network signal-to-noise ratio of 19. The binary is different from observations during the first two observing runs most notably due to its asymmetric masses: a ~ 30Mo black hole merged with a ~ 8Mo black hole companion. The more massive black hole rotated with a dimensionless spin magnitude between 0.22 and 0.60 (90% probability). Asymmetric systems are predicted to emit gravitational waves with stronger contributions from higher multipoles, and indeed we find strong evidence for gravitational radiation beyond the leading quadrupolar order in the observed signal. A suite of tests performed on GW190412 indicates consistency with Einstein's general theory of relativity. While the mass ratio of this system differs from all previous detections, we show that it is consistent with the population model of stellar binary black holes inferred from the first two observing runs.The authors gratefully acknowledge the support of the United States National Science Foundation (NSF) for the construction and operation of the LIGO Laboratory and Advanced LIGO as well as the Science and Technology Facilities Council (STFC) of the United Kingdom, the Max-Planck-Society (MPS), and the State of Niedersachsen/Germany for support of the construction of Advanced LIGO and construction and operation of the GEO600 detector. Additional support for Advanced LIGO was provided by the Australian Research Council.application/pdfen-AU© 2020 American Physical Societyhttps://creativecommons.org/licenses/by/4.0/202010.1103/PhysRevD.102.0430152020-12-20Creative Commons Attribution 4.0 International license