Ripple research

The

(STFC) has invested £7.1m over five years in gravitational wave research at

.

The scientists at the Institute for Gravitational Research will use the funding to upgrade wave detectors such as the Hanover, Germany-based Geo 600 and the US-based Laser Interferometer Gravitational-Wave Observatory (LIGO).

The devices are designed to detect ripples in space-time produced by black holes being formed or coalescing in the universe, which manifest themselves as very slight changes in the direction of gravitational force. Detectors such as the Geo 600 emit a laser beam that interferes with gravitational waves created between pairs of pendulums. The fluctuations in the amount of light coming out of the system, caused by the laser’s interaction with the waves, are then recorded on a computer database and later analysed by the scientists for signature fluctuations that represent the space-time ripples.

’So far, we have not detected anything,’ said Prof Jim Hough, director of the Institute for Gravitational Research. ’But, based on theoretical predictions about what the signal sizes should be, and on other observations in astronomy, we believe that we are getting to the stage where the sensitivities are such that we might detect something within the next few years.’

Although the LIGO is bigger and more sensitive than the Geo 600, Hough said that the smaller detector is more technologically advanced.

’The Geo 600 is a bit like a test bed for bigger detectors. It is more sophisticated than the LIGO in many ways, in the way that the inferorometer is done and the way that the pendulums are built,’ he said. ’The first thing we are going to do is export the technology from the Geo detector to the LIGO detectors. Then we will make the system called Advanced LIGO, which should be sensitive enough to guarantee detection of gravitational waves.’

Building of the the Advanced LIGO, to be carried out in the US, is scheduled to take place in 2010, and to be operational by 2014.

The scientists are also carrying out research to construct a more sensitive European detector, the Einstein Gravitational Telescope, which will be an extension of research done for the Geo 600 and another European detector, Virgo, near Pisa, Italy.

’We’re looking into better materials for the pendulums, which will have lower Brownian fluctuations. At any given temperature, atoms and molecules vibrate. This means that pendulums will move due to changes in temperature, and by choosing particular materials and by cooling we can reduce these fluctuations. So for the Einstein telescope we are looking to cool down towards liquid helium temperature and use silicon as a material for the pendulum and the mirrors.

’The present material is fused silica. Silicon would be similar in density, but it just happens to behave better when it is cooled to low temperatures to help reduce the thermal fluctuations,’ said Hough.

According to Hough, there are plans to build the Einstein telescope underground in a mine, which would help to reduce the fluctuations caused by gravity on the surface of the earth and ground vibrations.

A design study for the telescope, conducted by groups in Germany, France, Italy and the UK, will start in Spring 2008.