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Gravitational-Wave Emission
Gravitational waves are tiny ripples of the spacetime. These ripples are produced through the accelerated motion of heavy objects and they propagate as transversal waves outward from their source at the speed of light. While already proposed by Heaviside and Poincaré, it was Albert Einstein who had set the fundament for a correct interpretation and computation of these sources based on his Theory of General Relativity.
At the lowest order, gravitational-wave radiation can be approximated through the quadrupole formula
Gravitational waves transport energy and angular momentum and therefore, as gravitational radiation, a form of radiant energy similar to electromagnetic radiation.[7] Newton's law of universal gravitation, part of classical mechanics, does not provide for their existence, since that law is predicated on the assumption that physical interactions propagate instantaneously (at infinite speed) – showing one of the ways the methods of classical physics are unable to explain phenomena associated with relativity.
The first indirect evidence for the existence of gravitational waves came in 1974 from the observed orbital decay of the Hulse–Taylor binary pulsar, which matched the decay predicted by general relativity as energy is lost to gravitational radiation. In 1993, Russell A. Hulse and Joseph Hooton Taylor Jr. received the Nobel Prize in Physics for this discovery. The first direct observation of gravitational waves was not made until 2015, when a signal generated by the merger of two black holes was received by the LIGO gravitational wave detectors in Livingston, Louisiana, and in Hanford, Washington. The 2017 Nobel Prize in Physics was subsequently awarded to Rainer Weiss, Kip Thorne and Barry Barish for their role in the direct detection of gravitational waves.
In gravitational-wave astronomy, observations of gravitational waves are used to infer data about the sources of gravitational waves. Sources that can be studied this way include binary star systems composed of white dwarfs, neutron stars,[8][9] and black holes; events such as supernovae; and the formation of the early universe shortly after the Big Bang.
