GW190425

GW190425 was a gravitational wave detected^[1] on 25 April 2019 at LIGO-Livingston. Some low signal-to-noise data from the Virgo interferometer could not be used for detection but was used for parameter estimation.^[2] In contrast to GW170817, LIGO-Hanford was offline and did not observe GW190425, and because the Virgo detection was low-confidence, the event is not well-localized in the sky — the 90% confidence zone spans 8284 deg² (roughly 20% of the sky), while GW170817 was localized to 28 deg² (about 0.07% of the sky) before its optical counterpart was identified.^[2]

GW190425 was a compact binary coalescence with a signal to noise ratio 12.9.^[2] No electromagnetic event has been conclusively associated with GW190425; one candidate is FRB 20190425A in the galaxy UGC 10667.^[3] The signal could be result of a collision of two neutron stars, a neutron star and a low-mass black hole, or two low-mass black holes^[4] with a total mass of 3.4+0.3
−0.1 M_☉ and a chirp mass of 1.44+0.02
−0.02 M_☉, much heavier than any binary neutron-star system known from radioastronomy observations.^[2] The unusual mass has led to several different hypothesis for the origin of the signal. Some examples include:^[5] a neutron star might paired with 4-5 M_☉ Helium star might undergo common envelope evolution then supernova to produce an unusual binary neutron star,^[6] higher mass binary neutron stars may be preferentially created with either high or low magnetic fields explaining the lack of radioastronomy signals,^[7] and the possibility that the mass observation is at the extreme of a distribution characteristic of binary neutron stars.^[8]