Neutron star merger

A neutron star merger is the collision and coalescence of two neutron stars. It emits gravitational waves and can eject neutron-rich matter that forms heavy elements.

Binary neutron star: A gravitationally bound system of two neutron stars orbiting a shared center of mass. The merger is the final stage in the evolution of this compact binary.
Neutron star: A compact stellar remnant composed mainly of neutron-rich matter, typically about the mass of the Sun within a city-sized radius. The merger’s participants are neutron stars with immense density and strong gravity.
Neutron star binary formation: The astrophysical processes that create bound pairs of neutron stars, usually through successive stellar evolution and supernovae. A merger begins with a binary produced by the evolution of two massive stars.
Rapid neutron capture process: A sequence of rapid neutron captures and radioactive decays that creates many elements heavier than iron. Neutron-rich ejecta can host this process and forge heavy nuclei.
Binary black hole merger: The inspiral and coalescence of two black holes into a larger black hole. Unlike neutron-star mergers, these events generally lack dense stellar matter to eject.
Gravitational-wave inspiral: The gradual inward spiral of orbiting masses as they lose energy by emitting gravitational waves. Orbital energy loss brings the two neutron stars together before contact.
Gravitational wave: A propagating disturbance in spacetime produced by accelerating masses and traveling at the speed of light. The changing binary orbit radiates the signal that reveals the inspiral.
PSR B1913+16: A binary pulsar discovered in 1974 whose changing orbit provided evidence for gravitational-wave energy loss. Its orbital decay confirmed that compact binaries can inspiral before merging.
R-process nucleosynthesis: The formation of heavy elements through rapid neutron capture in environments rich in free neutrons. The merger is a candidate site for producing r-process elements such as gold.
Neutron star–black hole merger: The inspiral and coalescence of a neutron star and a black hole. Whether the neutron star is disrupted before crossing the horizon differs from two-star coalescence.

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