EU and Japan collaborate in search for gravitational waves
An exchange of know-how and technology between EU-funded scientists and their Japanese colleagues has paved the way for a new generation of ultra-sensitive gravitational wave detectors.
© #229152361 | Author: GiroScience, 2018 fotolia.com
Gravitational waves ripples in the fabric of space itself were first detected in 2015, almost 100 years after they were predicted by Albert Einstein. The discovery was made by an international collaboration using the two LIGO detectors in the United States.
Now the EU-funded ELITES project has helped pave the way for a new European detector, the Einstein Telescope, by facilitating cooperation between researchers in Europe and Japan, based on experience with a newly built Japanese detector called KAGRA. The new detector will answer fundamental questions in physics and cosmology.
The technologies developed during the project are also likely to have many applications in industry. These include finely tuned optical cavities that could provide extremely precise and stable time and frequency standards, techniques to isolate the detectors from seismic vibrations to levels not seen anywhere else, and new types of chemical bonding to assemble optical parts while cutting thermal noise.
Europe, the US and Japan have a long tradition of collaboration in gravitational wave research, says project coordinator Michele Punturo, of the European Gravitational Observatory near Pisa, Italy. So for us, KAGRA was the perfect place to test new technologies, and to learn many lessons about the difficulties we may find for the Einstein Telescope.
Distinctive bursts of gravitational waves are emitted when black holes or neutron stars collide. Detectors use lasers to sense minute changes in the separation of mirrors over distances of several kilometres as the waves pass. Six such collisions have been confirmed since 2015, two of them by the Virgo detector in Italy.
The KAGRA observatory, now nearing completion in central Japan, is a step up from earlier detectors. Its two arms, each three kilometres long, are placed in underground tunnels to decrease seismic vibrations. The laser optics use cryogenic cooling to reduce thermal noise and improve sensitivity.
ELITES was funded under the EUs Marie Skłodowska-Curie actions programme, which enabled EU scientists to travel to Japan. The Japanese government responded by funding their researchers to come to Europe.
European scientists learned about the problems of building a detector underground and how to manage the optics at a temperature of only 10 degrees above absolute zero. In return, Japanese researchers benefited from the optical coatings developed in Europe and expertise in mounting the optics to isolate them from vibration.
All these technologies will feed in to Europes Einstein Telescope which, like KAGRA, will be built underground with cryogenic cooling but with three arms, each 10 kilometres long. It will be the worlds most sensitive gravitational wave detector.
Beginning of a new era
Scientists are considering three candidate sites for the observatory: north-eastern Sardinia, the Mátra region of northern Hungary, and the border area between Belgium, the Netherlands and Germany.
A preliminary design, funded by the EU, was published in 2011 and detailed work is now moving forward. Construction is expected to start in 2025 with completion by 2030. This really is the beginning of a new era, Punturo says.
The reason we have to develop so many technologies is because of a statement by Einstein, he explains. Though Einstein predicted gravitational waves, he believed they would be too weak to detect. So, in proving that Einstein was correct in his prediction, we also had to prove that he was wrong! We needed 100 years but we have now developed the technology to detect gravitational waves..