22 May 2015

A major research project to find evidence of the existence of gravitational waves, ripples in space-time, was officially launched this week. The first direct detection of gravitational waves will open a new window to the otherwise invisible 'dark' side of the Universe and mark the beginning of an entirely new form of gravitational-wave astronomy.
UK researchers supported by STFC have played a major role in developing the Advanced Laser Interferometer Gravitational-wave Observatories (aLIGO) project.
Gravitational waves are ripples in space-time that are emitted by cataclysmic cosmic events such as exploding stars, merging black holes and/or neutron stars, and rapidly rotating compact stellar remnants. The existence of gravitational waves was predicted in 1916 by Albert Einstein as a consequence of his general theory of relativity but the waves have never been observed directly.
Based at the LIGO Hanford facility in the USA, the 4-km-long L-shaped LIGO interferometers use a laser split into two beams that travel back and forth down long beam tubes from which the air has been evacuated. The beams are used to monitor the distance between precisely configured mirrors. According to Einstein's theory, the relative distance between the mirrors will change very slightly when a gravitational wave passes by.
The original configuration of LIGO, which operated from 2002-2010, was sensitive enough to detect a change in the lengths of the 4-km arms by a distance one-thousandth the size of a proton. LIGO and UK scientists from STFC's Rutherford Appleton Laboratory, and the Universities of Cardiff, Birmingham, Glasgow and Strathclyde, have contributed to the upgrade of the LIGO hardware to form a newer, even better Advanced LIGO facility.
The new detector will increase the sensitivity of the LIGO instruments by a factor of 10 and provide a 1,000-fold increase in the number of astrophysical candidates for gravitational wave signals. The aLIGO instruments should detect multiple gravitational-wave events each year.
UK researchers supplied the suspension technology which holds the interferometer's mirrors in place, and part of its optical system. The team will also prepare data analysis computing systems in readiness for engineering and science data runs scheduled to start later in the year.
Professor Kenneth Strain, deputy director of the IGR and principal investigator of the Advanced LIGO project team in the UK said "The aLIGO project is immensely important in developing our understanding of the universe, and we're pleased and proud to have been involved from the start following our close involvement with the original LIGO initiative."

Image: Researchers installing some of the small suspended LIGO mirrors in the vacuum system.