GW190412: Observation of a binary-black-hole coalescence with asymmetric masses

We 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 ∼30 M ⊙ black hole merged with
a ∼8 M ⊙ 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.