Kilonova occurs in a compact binary system when two neutron stars or a neutron star and a black hole merge. 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.
These events are thought to be responsible for producing most of the heavy elements such as gold and platinum.
They are 1/10 to 1/100 the brightness of a typical supernova, the self-detonation of a massive star.
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 spacecraft and then observed using the Hubble Space Telescope 9 and 30 days after burst.
The inspiral and merging of two compact objects are a strong source of gravitational waves. Thanks to this on October 16, 2017, the LIGO and Virgo collaborations announced the first simultaneous detections of gravitational waves (GW170817) and electromagnetic radiation 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 located in a relatively nearby galaxy, NGC 4993.,
In October 2018, astronomers reported that GRB 150101B, a gamma-ray burst event detected in 2015, may be analogous to the historic GW170817.
The similarities between the two events, in terms of gamma ray, optical and x-ray emissions, as well as to the nature of the associated host galaxies, are considered “striking”, and this remarkable resemblance suggests the two separate and independent events may both be the result of the merger of neutron stars, and both may be a hitherto-unknown class of kilonova transients.
Kilonova events, therefore, may be more diverse and common in the universe than previously understood, according to the researchers.