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The fusion of two hyperdense stars is making waves through the universe

​Using a variety of sensors, physicists around the world examined the region from which a gravitational wave originated. This wave was detected on August 17, 2017 by the Ligo-Virgo facilities, in the search for other messengers from the universe. Created from the fusion of two neutron stars, this wave was accompanied by a burst in gamma rays as well as visible light emission, which was detected in particular by the Integral satellite and the VLT, with a major role played by the Irfu. Regarding neutrinos, the researchers analyzed their data without finding any candidates.

Published on 20 November 2017

Thanks to the Integral satellite, astrophysicists from the Irfu demonstrated that the wave of August 17 was associated with a gamma ray burst, a brief surge of gamma rays emitted just two seconds after the fusion of the stars. Aiming one of the giant telescopes of the Very Large Telescope (Chile), the scientists also participated in studying the emission of visible light that followed this event, establishing in particular that this light was not polarized.

Unlike the four gravitational waves previously detected, this space vibration, named GW170817, did not result from the fusion of two black holes but from the fusion of two neutron stars, which are the densest known stars.

The particle physicists at Irfu also analyzed the data collected by the Antares and Hess experiments. This shows that wave GW170817 did not give off any detectable neutrino emissions or very high energy gamma rays.

The study of this phenomenon, which had never been directly observed before, opens up many possibilities, especially a better understanding of the origin of the very heavy elements in the universe, and a completely new way to measure the rate of expansion of the universe.

The ensemble of these exceptional results was published on October 16, 2017 in a series of articles appearing in the journals Nature, Astrophysical Journal, and Physical Review Letters.

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