A kilonova (macronova or r-process supernova) is a transient astronomical event that occurs in a compact binary system when two neutron stars or a neutron star and a black hole merge into each other. Kilonovae are thought to emit short gamma-ray bursts and strong electromagnetic radiation due to the radioactive decay of heavy r-process nuclei that are produced and ejected fairly isotropically during the merger process.
The first kilonova to be found was detected as a short gamma-ray burst, sGRB 130603B, by instruments on board the Swift Gamma-Ray Burst Explorer and KONUS/WIND spacecrafts and then observed using the Hubble Space Telescope.
The inspiral and merging of two compact objects are a strong source of gravitational waves (GW). Kilonovae are thought to be progenitors of short gamma-ray bursts (GRB) and the predominant source of stable r-process elements in the Universe. The term kilonova was introduced by Metzger et al. in 2010 to characterize the peak brightness, which they showed reaches 1000 times that of a classical nova. The basic model for neutron star mergers was introduced by Li-Xin Li and Bohdan Paczyński in 1998.
The first clear detection of a kilonova was in 2013, in association with the short-duration gamma-ray burst GRB 130603B, where the faint infrared emission from the distant kilonova was detected using the Hubble Space Telescope.
On October 16, 2017, the LIGO and Virgo collaborations announced the first simultaneous detections of gravitational waves (GW170817) and electromagnetic radiation (GRB 170817A, SSS17a) of any phenomena, and demonstrated that the source was a kilonova caused by a binary neutron star merger. This short GRB was followed by a longer transient visible for weeks in the optical electromagnetic spectrum (AT 2017gfo) located in a relatively nearby galaxy, NGC 4993.
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