On February 11, 2016, the Ligo and Virgo* collaborations announced that they had detected gravitational waves. This was a double masterstroke, as in detecting these waves for the first time—a century after Einstein had described them—researchers also observed their first ever collision between two black holes.
To detect the passage of a gravitational wave, the Ligo and Virgo detectors have to be able to measure infinitesimal movements—around a billionth of the size of an atom. A new window has opened onto the universe. These gravitational waves were detected on September 14, 2015 at 11.51am Paris time (9.51am GMT), by the twin LIGO (Laser Interferometer Gravitational-Wave Observatory) detectors in the United States, one in Livingston, Louisiana and the other in Hanford, Washington.
Waves bearing precious information
Gravitational waves are produced by cosmic cataclysms in our galaxy and beyond, and propagate through the universe at the speed of light. Since they interact very little with matter, they arrive practically intact from where they were first emitted. It has long been thought that if astrophysicists succeeded in capturing these waves, they would have at their disposal a unique means of studying the cosmos and access to information that no other methods of observation can provide. Gravitational waves might also inform researchers about the very first moments of the universe, since those emitted by the Big Bang are, in theory, still perceptible. Finally, their detection would be further confirmation of Einstein's predictions.
According to the theory of general relativity, every massive object distorts spacetime in its neighborhood. When such an object is accelerated, these deformations propagate, a little like ripples on the water's surface. These are gravitational waves, and they are only caused by very violent astrophysical events, for example, when two neutron stars or two black holes rotate around each other and then merge, or when a massive star explodes into a supernova. So by observing gravitational waves, astronomers hope to better understand these phenomena, which have so far eluded their grasp.
*The Linear Accelerator Laboratory (CNRS/Université Paris-Sud) has been involved in the Virgo collaboration for 25 years with other laboratories.
On Friday, February 12, French researchers from the LIGO/Virgo consortium will be on Twitter from 1.30pm to 2pm to answer questions about the exceptional detection of gravitational waves. You can submit your questions already with #AskLVC!
- Article published in Physical Review Letters: "Observation of gravitational waves from a binary black hole merger, the LIGO Scientific Collaboration and the Virgo Collaboration." Physical Review Letters, le 11 février 2016. http://link.aps.org/doi/10.1103/PhysRevLett.116.061102
- Journal du CNRS (in French): https://lejournal.cnrs.fr/articles/a-detecte-des-ondes-gravitationnelles ; https://lejournal.cnrs.fr/articles/a-la-poursuite-des-ondes-gravitationn... et https://lejournal.cnrs.fr/articles/ondes-gravitationnelles-en-vue
- CNRS press release (in French): http://www2.cnrs.fr/presse/communique/4409.htm
- Video in Journal du CNRS (in French): https://lejournal.cnrs.fr/videos/ondes-gravitationnelles-les-detecteurs-...
- Article by Paris-Sud University (in French): http://www.actu.u-psud.fr/fr/recherche/actualites-2016/detection-des-ond...
Find out more:
- VIRGO : https://www.ego-gw.it/public/virgo/virgo.aspx
- LIGO : http://www.ligo.org/
- LAL & Virgo : https://groups.lal.in2p3.fr/virgo/
Simulation of gravitational waves generated by the collision of two black holes (c) C. Henze/Nasa/Goddard Space Flight Center