Let’s remember that it was at the end of 2015 that the scientific community celebrated the 100th anniversary of Einstein’s formulation of his gravitation theory. What some scientists already knew – but kept it secret – was that the Ligo gravitational wave detectors in the US had shortly before made the first direct detection on Earth of the passage of a stream of gravitational waves. They deform the geometry of spacetime, as a wave would on the surface of water or in an elastic medium, like the interior of our blue planet, when seismic waves pass.
Early the following year, the noosphere finally learned that the era of gravitational wave astronomy had begun on September 14, 2015, with the detection on Earth of the gravitational wave source GW150914, where GW is the abbreviation for Gravitational wave, English. The signal analysis had been carried out by members of the Ligo collaboration, but also by Virgo in Europe. The signal detected by Ligo came from recent events, when two stellar-mass black holes forming a binary pair approach each other in a spiral and then merge into a single compact star (see the videos below). It should be remembered that France and Italy are very involved theoretically and observationally in the study of gravitational waves with the Virgo detector, as shown by the award of one of the CNRS gold medals for Alain Brillet and Thibault Damouras well as the existence of large teams working in laboratories such as LAPP (Annecy Particle Physics Laboratory) or the Observatory of the Côte d’Azur (OCA) in Nice, Artemis.
A video presentation of Virgo and the hunt for gravitational waves. © CNRS
From Ligo to Kagra and into the future eLisa
Futura took the opportunity to interview several times one of the members of Artemis, the astrophysicist Olivier Minazzoli, who also works at the scientific center in Monaco. He had e.g. given us several explanations about the possibility of test of superstring theory with Jomfru and Ligo as well as the opportunity to achieve a highly convincing proof of the existence of black holes by highlighting the influence of what are called their quasi-normal states on the spectrum of gravitational waves resulting from the merger of two black holes.
The creators of Ligo in the USA, the American physicists Rainer Weiss, Kip S. Thorne and Barry C. Barish, received the Nobel Prize in Physics shortly after – they can be seen presenting their discoveries and achievements in the two videos below. Ligo and Virgo were to discover, in the years to come, numerous collisional sources of gravitational waves, mergers of two black holes, collisions between two neutron stars and, more rarely, collisions between black holes and neutron stars. These are not yet events involving supermassive or intermediate mass black holes, we will have to wait for the horizon of the 2030s with the detector in the room eLisa.
Between each search campaign, the detectors are upgraded to become more sensitive and thus able to detect more distant events and to derive more precise information about those events, such as the masses, the angular momentums of the black holes, and finally. put new constraints on relativistic theories of gravitation alternatives to Einstein’s theory.
These upgrades require breaks and due to the Covid-19 pandemic, Ligo, Virgo and also their Japanese cousin, Kagra, had not observed anything since 2020. The members of Ligo let it be known that they were again hunting for the ether. Virgo will be a little behind in his schedule, as he will not join Ligo in his research until the end of summer, or even the beginning of autumn 2023. Kagra has also resumed his hunt, the same day as Ligo, ie. 24 May 2023.
Ligo and the Hunt for Gravitational Waves I. For a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Select “French”. © LIGO Lab Caltech: MIT
Black hole mergers, but also supernovae
Ligo’s sensitivity has therefore been increased, so that the machines should be able to detect black hole collisions on average every two or three days instead of once a week.
Scientists now hope to detect the gravitational waves emitted when a star begins the collapse that will lead to it exploding as a supernova. This detection is currently limited to the Milky Way, but we have good hopes of detecting such an event probably before 2050, with any luck..
On the education there is also detection of waves emitted by rotating neutron stars due to the presence of “mountains” on their surface. A perfect sphere could not emit these waves according to Einstein’s theory.
These recent advances have been made possible in particular by using laser beams with “compressed” electromagnetic waves. These are techniques to prepare a laser beam of photons by limiting as much as possible the quantum blur, which is mainly due to the famous Heisenberg inequalities.
Ligo and the Hunt for Gravitational Waves II. For a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Select “French”. © LIGO Lab Caltech: MIT
To conclude this article, let us remember a children’s book about gravitational wave astronomy. We owe that to two recognized specialists in this new science: Tania Regimbau and Mairi Sakellariadou. Here is their brief presentation of the book.
“ The idea for this book was born on a beach in Nice in September 2017, two years after the first detection of gravitational waves. This discovery shook the scientific world, as it was the ultimate confirmation of Albert Einstein’s theory, but also because it marked the beginning of a new era in astrophysics. The detection of gravitational waves was rewarded with Nobel Prize in Physics 2017.
As both members of the collaboration that made this discovery, we felt the desire to pass it on to children. Then we imagined a space tale with two twin stars who loved each other so much that they fused together to be together forever.
From there, the first story in this book was born, which marked the beginning of a new adventure for us, as three other stories followed… “.
