Message from leader

Leader, Takahiro Tanaka, Kyoto University, Division of Physics and Astronomy
The gravitational waves were predicted by Einstein’s general relativity and their direct detection was awaited for many years. Finally, the first gravitational wave direct detection by LIGO was announced in February 2016. In general relativity time and space are curved and all objects in the absence of force other than gravity move straight on the curved spacetime. Gravitational waves are the ripples of this space-time curvature that propagate as waves.
Direct observations of gravitational waves have just begun. We have the chance to grasp new scientific discoveries. Indeed, various breakthroughs are being brought about by gravitational wave observations. The first gravitational wave detection by LIGO has brought about an amazing discovery that there are many binaries consisting of black holes about 30 times heavier than the Sun in our universe, whose origin is now a big issue of debate. In addition, it also gets to be possible to test gravity theories using actual data of gravitational waves. Gravitational waves from the coalescence of binaries including neutron stars are also expected to be detected in the near future.
 By observing the counterparts by means of electromagnetic waves, it is expected that we can unravel the origin of gamma ray bursts as well as the origins of heavy elements such as gold and platinum in the universe. A supernova explosion is also one of expected gravitational wave sources. Once it occurs in the vicinity, our understanding of the explosion mechanism of supernovae will progress rapidly.
 There are three advantages in promoting gravitational wave research in Japan. The first is the existence of KAGRA, a large-scale gravitational wave detector in Japan. Correspondingly, a gravitational wave data analysis team is organized, and a unique flexible analysis library, KAGALI, is under development. It is also expected to start to obtain original gravitational wave data from 2019.
 Secondly, there are organized teams for observing the counterparts of gravitational wave sources, and also unexpected objects by pointing the telescope quickly to the direction of gravitational wave signal. In particular, the Subaru Telescope/HSC is a worldwide remarkable facility with its high sensitivity and wide field of view. Also, the impact of simultaneous observations of supernova explosion by means of gravitational waves and super KAMIOKANDE is immeasurable. We are also ready for observations by X-rays and gamma rays for the expected counterparts, such as short gamma ray bursts.
 Thirdly, there is a long history in gravitational wave theoretical research in Japan. An international workshop on general relativity and gravity has been held annually. In the field of numerical simulation in which "K computer" is available, important research results are produced from Japan, e.g., in numerical relativity and in 3-d simulations of supernova explosion.

Currently, international competition to grab the opportunities for this scientific major discovery is severe. In order to show our presence, it would be effective to bring together these three advantages and construct a tight research network, which at the same time makes it possible to train young researchers who can drive the future development of gravitational wave physics and astronomy. As project researches, we focus on strong gravity, origins of black hole binaries, short gamma ray bursts, origins of r-process elements, supernova explosion mechanisms, and so on.

As a vision for the management of this innovative area, we raised three themes: synergy effect, international competitiveness and training young researchers. Keeping these three themes in mind, we wish to advance collaborative research. Let's make a historical research achievement together, and write the pages of the genesis of gravitational wave physics and astronomy.