GW170817

GW170817 was a gravitational-wave signal from two merging neutron stars, detected on 17 August 2017 alongside light and other electromagnetic radiation.

Neutron star merger: An event in which two neutron stars orbit, lose energy, and collide. This merger generated GW170817’s gravitational waves and electromagnetic signals.
LIGO: A pair of laser interferometers in the United States that detect gravitational waves. Its detectors recorded the signal’s long inspiral from the merger.
Multi-messenger astronomy: The study of an astronomical source through multiple carriers of information, such as light and gravitational waves. GW170817 established a landmark case combining gravitational waves with electromagnetic observations.
Binary neutron star: A gravitationally bound system containing two neutron stars. The existence of such binaries made a merger like GW170817 predictable.
Neutron star equation of state: A relation describing how pressure, density, and other thermodynamic quantities behave inside neutron-star matter. GW170817 constrained this relation without uniquely determining the composition of dense matter.
Gravitational-wave astronomy: The study of the universe using ripples in spacetime produced by accelerating masses. The signal was a landmark observation in this emerging field.
Virgo interferometer: A European laser interferometer near Pisa designed to detect gravitational waves. Its data helped constrain the merger’s position in the sky.
Standard siren: A gravitational-wave source whose signal can provide a distance estimate independent of the cosmic distance ladder. Its waveform supplied a distance that could be paired with the host galaxy’s recession.
Hulse–Taylor binary: The binary pulsar discovered by Russell Hulse and Joseph Taylor in 1974. Its orbital decay provided early indirect evidence for gravitational-wave emission from compact binaries.
Neutron star-black hole merger: A compact-binary merger in which a neutron star spirals into a black hole. Comparing future events can distinguish neutron-star merger signatures from other compact-object collisions.

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