Neutron star merger

On 17 August 2017, the LIGO and Virgo interferometers observed GW170817,[7] a gravitational wave associated with the merger of a binary neutron star (BNS) system in NGC 4993, an elliptical galaxy in the constellation Hydra about 140 million light years away.

The subsequent detection of Swope Supernova Survey event 2017a (SSS17a)[14] in the area where GW170817 and GRB 170817A were known to have occurred—and its having the expected characteristics of a kilonova—strongly imply that neutron star mergers are responsible for kilonovae as well.

[17] Later that year, astronomers reported that GRB 150101B, a gamma-ray burst event detected in 2015, may be directly related to GW170817 and associated with the merger of two neutron stars.

[18][19][20][21] Also in October 2018, scientists presented a new way to use information from gravitational wave events (especially those involving the merger of neutron stars like GW170817) to determine the Hubble constant, which establishes the rate of expansion of the universe.

[24] In April 2019, the LIGO and Virgo gravitational wave observatories announced the detection of GW190425,[25] a candidate event that is, with a probability 99.94%, the merger of two neutron stars.

[37] These high-energy gamma ray photons would extinguish life directly, through thermal stress, molecular breakdown, and terminal radiation damage to both plants and animals.

Apart from an unlucky hit by a directed beam, any neutron star merger occurring within 10 parsecs of Earth would also result in conclusive human extinction.

[39][40] Relative to supernovae, binary neutron star (BNS) mergers influence about the same volume of space, but are thought to be much rarer, and their most dangerous sGRB component requires that the beam be precisely oriented towards the Earth.