Neutron star merger

Coalescence of a binary containing two neutron stars can eject neutron-rich material and power a kilonova. Rapid neutron-capture process reactions in the ejecta produce heavy elements. This connects compact-binary dynamics to chemical enrichment.

The 17 August 2017 binary-neutron-star merger detected through gravitational waves, with a short gamma-ray burst and a multiwavelength counterpart including a kilonova. Its joint observations connected compact-binary inspiral, relativistic outflows and heavy-element-rich ejecta.

If a circular compact binary has a gravitational wave coalescence delay $t=B{A}_0^4$ and $dN/d{A}_0$ is constant, then $dN/dt=(dN/d{A}_0)|d{A}_0/dt|\propto t^{-3/4}$. More generally $dN/d{A}_0\propto A_0^{\beta }$ gives a delay-time distribution proportional to $t^{(\beta -3)/4}$. A log-uniform separation distribution instead gives $t^{-1}$.

An optical and infrared transient powered by radioactive decay in material ejected from a compact-object merger. Its evolving spectrum and light curve probe ejecta composition and rapid neutron-capture process production.