EGO-ICRR gravitational wave meeting
A meeting between the European Gravitational Observatory [EGO] and the Institute for Cosmic Ray Research [ICRR], on the topic of gravitational wave research, was held at the University of Tokyo’s Kashiwa campus on 4-5 October this year.
The meeting, held within the framework of “Italy in Japan 2011”, was intended to foster the collaboration between the Large-scale Cryogenic Gravitational wave Telescope [LCGT], which has been recently funded for construction in the Kamioka mine; and the Virgo Gravitational Wave Observatory, which has been in operation for several years and is presently undergoing a major upgrade. A total of 37 scientists attended this fruitful meeting.
Detecting gravitational waves is extremely difficult, as it involves the detection of the relative displacement of suspended masses, smaller than 10-20 m, over distances of a few kilometers.
Virgo, the LIGO observatories in the United States and GEO in Germany were designed with a sensitivity that allows only a small probability each year of detecting a gravitational wave train from a stellar inspiral. Virgo and LIGO are currently undergoing upgrades to improve their sensitivity.
These upgraded observatories, along with the LCGT, are designed with a sensitivity ten times higher than present – and will be sensitive to neutron star – neutron star inspirals as far away as 250-300 mega parsecs. This will allow several gravitational wave detections each year. The commissioning of these advanced interferometers will mark the starting of gravitational wave astronomy.
Detection of a gravitational wave, from black holes and neutron star inspirals, is mostly non-directional. The synchronous detection of a train of gravitational waves, by a network of observatories around the world, will allow triangulation of the source, in the sky.
The addition of the LCGT observatory – thousands of kilometers away from the existing installations – will strengthen the gravitational wave detector network and greatly improve its pointing capabilities.
The LCGT detector arms will embrace Super-Kamiokande, and the other ICRR neutrino and dark matter experiments contained within the Kamioka mine. Such a close proximity to neutrino detectors is of importance to explore the correlated detection of neutrinos expected from supernova outbursts or neutron star disruption, when it plunges into a black hole during the last phases of an inspiral. Other neutrino detectors and electromagnetic telescopes around the world, will try to correlate other emissions from these sources, once the gravitational wave network has detected an event and indicated a direction.
The LCGT will have a structure very similar to Virgo’s – as such, the latter observatory will provide its extensive experience, in controlling and operating a suspended interferometer sensitive to gravitational waves of a low frequency (down to 10 Hz), to LCGT.
The LCGT will be the first gravitational wave observatory built underground, as well as the first to be ultimately cooled to cryogenic temperatures. As such, it will probe the key technologies which will be used to constructing the third generation European gravitational wave observatories, such as the Einstein Telescope. This will be designed to be sensitive to gravitational waves below 10 Hz – and to be able detect stellar inspirals over a large fraction of the visible universe.
Due to its underground location in high rigidity rock, the LCGT will be less exposed to Newtonian noise – seismically excited fluctuations of the Earth’s gravitational field that, on the planet’s surface, overwhelm the action expected from the incoming gravitational wave train in the frequency range below 10Hz.
Therefore, although initially addressing the same frequency range covered by LIGO and Virgo, the LCGT has the potential to extend its sensitivity at lower frequencies.
The European Gravitational Observatory is an associate member of the European Physical Society.
