Kilonova

A kilonova (also called a macronova) is a transient astronomical event that occurs in a compact binary system when two neutron stars (BNS) or a neutron star and a black hole collide.^[1] The kilonova, visible over the weeks and months following the merger, is an isotropically expanding luminous afterglow of electromagnetic radiation emitted by the radioactive decay of r-process nuclei synthesized by—and then ejected from—the initial cataclysmic event.^[2][3]

The high sphericity of kilonovae through its early epochs was deduced from the blackbody nature of the spectrum observed for the most important recorded BNS merger, GW170817 / AT2017gfo.^[4][5]