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Gravitational waves

According to the theory of General Relativity, any mass or energy modifies the geometry of the spacetime, that means that they change the distances and the time measured with a rule and a clock. If the mass has an asymetric accelerated motion, those spacetime changes can propagate like a wave on water surface : this is a gravitational wave. More information is available on the Virgo web site.

When a massive star explodes as a supernova, when a black hole is created, when a neutron star rotates and emits periodically an intense electromagnetic radiation or when two neutron stars inspirals around each other, gravitational waves can be emitted. They are so tinily absorbed by the matter that we can detect them on Earth even when they come from sources several million light-years away.

A first indirect evidence of the existence of gravitational waves has been obtained thanks to a neutron stars binary system PSR1913+16, discovered in 1974 by Russell Hulse and Joseph Taylor. Using the Doppler effect, the measure of the orbital speed of one of those two stars, done by Joel Weisberg and Jospeh Taylor over more than 30 years, have shown that the orbital period decrease is in in full agreement with the hypothesis of gravitational waves emission.

Since September 14th 2015, the LIGO-Virgo collaboration has provided the first direct evidence of the existence of the gravitational waves.