gravitationalwave

Gravitational waves are disturbances in the fabric of spacetime produced by accelerating masses, as predicted by Einstein's general relativity. They propagate at the speed of light and carry energy, angular momentum, and information about their sources.

In the weak-field, far from sources, gravitational waves can be described by small metric perturbations that are transverse and traceless. They cause tiny changes in the separation of freely falling test masses, measurable as strain h.

The strongest sources are astrophysical: mergers of compact binaries—black holes and neutron stars—and explosive events like core-collapse supernovae. Stochastic backgrounds may arise from a superposition of many distant sources or from processes in the early universe such as inflation.

Detection relies on highly sensitive instruments. Ground-based laser interferometers such as LIGO, Virgo, and KAGRA observe in the tens to thousands of hertz range. Space missions like the planned LISA will target millihertz frequencies. Pulsar timing arrays probe nanohertz waves using precise pulsar signals.

The concept dates to 1916, with indirect evidence obtained in the Hulse–Taylor binary pulsar in 1974. Direct detections began in 2015 with GW150914, later followed by numerous events including binary neutron star GW170817, which was associated with a gamma-ray burst.

Gravitational waves enable tests of general relativity in strong gravity, measurements of black hole and neutron star properties, and insights into the dense matter equation of state. They also constrain the speed of gravity and the graviton mass, and enable multimessenger astronomy.