17 August 2017 12:41 GMT: Alert!
The final collision was extremely bright, emitting an intense "fireball" of gamma rays. You can see it in the video below. The large bright spot in the center is galaxy NGC 4993. Just above and to the left, you can see GW170817 turning from intense blue to red.
Race against the clock
Neutron stars are remnants of massive stars. A giant star dies when it explodes, giving birth to a supernova. This extremely luminous phenomenon lasts only a few days to a few weeks: once the explosion is over, only a very dense core composed almost entirely of neutrons remains - a neutron star. It is the size of a city like London, but a teaspoon of its material weighs about a billion tons, the equivalent of 100,000 Eiffel Tower. Neutron stars are the smallest and densest stars known to date. Just like the ordinary stars from which they come, some stars evolve in pairs. They then orbit around each other and slowly approach each other, losing energy in the form of gravitational waves - a process that eventually accelerates to fusion. If this scenario was predicted by models, this is the first time it has been confirmed by observation.
And the adventure isn't over: " we've got enough data to work with for a long time! ", enthuses Benoît Mours. Alain Brillet, the French scientist who developed the Virgo gravitational interferometer, adds in the Journal du CNRS : " These results, which sign the birth certificate of multi-signal astronomy, are proof that we did not work for nothing. And they offer a hundred years of work to our successors! "A feat that allows scientists from all over the world to party, a great party!