The world watched agog last week as scientists of the LIGO Scientific Collaboration and Virgo Collaboration announced that they had observed for the first time, gravitational waves, produced by the merger of two massive black holes about 1.3 billion light years from the Earth and detected by the LIGO instruments on 14th Sept 2015.This detection confirmed the theoretical prediction made by Albert Einstein one hundred years ago, from his General Theory of Relativity, and opened a whole new window on the Universe.In this special report you can read about how SUPA scientists, at the Universities of Glasgow, Strathclyde and the West of Scotland, led by the Institute for Gravitational Research at the University of Glasgow, made key contributions to this remarkable discovery - hailed by many as the scientific breakthrough of the century.
Scotland has been active in the gravitational waves field since the 1970s, initially using bar detectors in the Glasgow group. This evolved into using free mass systems with interferometric length sensing. This approach of using interferometry had also been started by a group in Munich in Germany and one at MIT. Initial experiments at Glasgow rapidly evolved to the building of a 10m-long detector within the (then) Department. Under Jim Hough's leadership this further led to the GEO 600 detector, built jointly with colleagues in Germany. Meanwhile, Prof Ron Drever moved from Glasgow to Caltech, helping combine the Caltech and MIT efforts in their evolution to the initial LIGO project. In 2009, Sheila Rowan took over from Jim in leading the Glasgow group. Crucial technical developments pioneered in GEO 600 have been transferred to LIGO, enabling it to evolve into the Advanced LIGO that has now made the first direct detection of gravitational waves.
Advanced LIGO consists of interferometric gravitational-wave detectors at two sites, one in Hanford (Washington State, USA) and one in Livingston (Louisiana, USA). At the turn of the century IGR scientists worked within the LIGO Scientific Collaboration – a global partnership of around 1000 scientists - to propose methods and designs that would allow at least 10 times greater sensitivity than the initial LIGO detectors, vastly extending their science potential. In particular, two Glasgow-originated and developed technologies were selected as essential elements of the design: quasi-monolithic fused silica suspensions on which the mirrors in the Advanced LIGO detectors hang, and signal recycling. Both of these techniques were essential features of the German-British GEO600 detector. In particular the silica suspensions – which both isolate the mirrors from ground vibrations and, crucially, minimise the thermally induced vibrations of the mirrors, where a critical technology in enabling this first detection to be made.
The Advanced LIGO UK consortium supplying the suspension, led by Ken Strain in Glasgow, worked in parallel with GEO colleagues at the Leibniz Universität Hannover – who supplied the laser for Advanced LIGO. Together these major contributions made the UK and Germany key partners in Advanced LIGO. Today, we stand poised at the start of gravitational astronomy, with developments in progress for even more sensitive detectors both on the ground and in space. The UK and Germany again are working together in an international partnership towards the eLISA space-based gravitational wave detector, with a demonstrator mission – LISA Pathfinder - currently flying carrying optical bench technology developed in Glasgow under the leadership of Harry Ward.
With the Advanced Virgo detector soon to come online, the KAGRA in Japan under construction, and the latest announcement of a third Advanced LIGO detector to be sited in India, the future in gravitational waves looks bright.