Optical emission from a kilonova following a gravitational-wave-detected neutron-star merger

Understand

The merger of two neutron stars has been predicted to produce an optical-infrared transient (lasting a few days) known as a 'kilonova', powered by the radioactive decay of neutron-rich species synthesized in the merger.

• Evidence that short gamma-ray bursts also arise from neutron-star mergers has been accumulating.
• In models of such mergers a small amount of mass ($10^{-4}$-$10^{-2}$ solar masses) with a low electron fraction is ejected at high velocities (0.1-0.3 times light speed) and/or carried out by winds from an accretion disk formed around the newly merged object.
• This mass is expected to undergo rapid neutron capture (r-process) nucleosynthesis, leading to the formation of radioactive elements that release energy as they decay, powering an electromagnetic transient.