Investigations in Gravitational Radiation

Einstein's General Theory of Relativity (GR) predicts that dynamical systems in strong gravitational fields will release vast amounts of energy in the form of gravitational radiation. Gravitational waves are ripples in the fabric of spacetime and travel from their sources at the speed of light, carrying information about physical processes responsible for their emission, obtainable in no other way. They are among the most elusive signals from the deepest reaches in the Universe. Experiments aimed at detecting them have been in development for several decades, and are now reaching sensitivity levels where detection is expected within a few years.

The worldwide network of interferometric detectors includes the German-UK GEO600, the French-Italian Virgo, the American Laser Interferometer Gravitational-Wave Observatory (LIGO) and is being enhanced with a new detector under construction - KAGRA in Japan. The former detectors have all reached sensitivities close to their design goals and have taken the most sensitive data to date. Cooperation amongst different projects enables continuous data acquisition, with sensitivity to a wide range of sources and phenomena, over most of the sky.

Data from GEO, LIGO and Virgo, have already increased our understanding of astronomical phenomena. Search for gravitational waves at the times of 154 gamma-ray bursts has allowed the best ever exclusion distances and provided evidence for extra-Galactic sources of soft-gamma repeaters. The distance reach for binary black holes in the most recent runs is 300 Mpc and the rate upper limits are now very close to that expected in some of the astrophysical models. The search for gravitational waves from the Vela pulsar has set an upper bound on the strength of radiation that is significantly below that expected from the observed spin down rate of the pulsar, corresponding to a limit on the star's ellipticity of a part in a thousand.

While recent and current observations may produce detections, there can be no guarantees. However, there is great confidence that the advanced detectors currently in construction will routinely observe gravitational waves. The advanced LIGO detectors are based on the quasi-monolithic silica suspension concept developed in the UK for GEO 600 and on the high power lasers developed by our German colleagues in GEO 600. The Advanced Virgo detector also uses a variant of the silica suspension technology. The Cardiff and Glasgow groups have initiated and led searches for astronomical sources, thanks to the algorithmic and analysis effort that has been supported since the first data taking runs began eight years ago.

We propose a programme that leads to full exploitation of data from Advanced LIGO (aLIGO), building on both continuing operation of GEO600 and analysis of data taken in the most recent LIGO/Virgo science runs. In particular we will model binary black hole mergers and carry out
deep searches for
* coalescing binary neutron stars, neutron star-black hole binaries, and black hole binaries
* bursts of gravitational waves that may originate from supernovae,
* continuous signals from pulsars and other rotating neutron stars,
* gravitational waves detected by cross-correlation methods, including a cosmological background.

In parallel, we propose detector research and development. Detector sensitivity is mainly limited by thermal noise associated with the substrates of the mirrors, their reflective coatings, and their suspension elements, as well as by noise resulting from the quantum nature of the light used in sensing. Our research is targeted towards making innovative improvements in these areas. We have major responsibilities for the silica suspensions in aLIGO, and in the development of enhancements and upgrades to the aLIGO detectors, in the areas of mirror coatings for low thermal noise, silicon substrates, cryogenic suspensions and improved interferometer topologies to combat quantum noise.

There are numerous beneficiaries from our proposed research in gravitational waves, including industry, other academic disciplines, schools, science centres, museums and the general public. Materials, techniques and computational software created during the design and manufacture of gravitational wave detectors and the analysis of their data, have found numerous uses and applications in industry and other fields of academic research. E.g. the Triana software package that we developed has been used on many industrial and interdisciplinary collaborative projects to date, including: BDWorld (UK); GridLab, CoreGRID and Provenance (EU); GriPhyN and Pegasus (USA). Further, our studies of mirror coating thermal noise have played a key role in the Stanford-Scotland Photonics Innovation Collaboration, designed to capitalise on leading research in the photonics sector.

Our novel oxide bonding technology is the subject of contract research studies with optics companies in the UK and Germany, and a KTP is funded in the UK to transfer the technology in detail to a UK company specialising in the construction of optical components. We are also implementing our planned extensive knowledge exchange activities ranging from optics and engineering to a study of cell behaviour and response to nano-mechanical stimulation, an area of importance for wound healing. The technology for the thin, strong fused silica fibres supporting the 40kg aLIGO mirrors masses has led to partnerships with industry on novel all-silica gravimeters for the oil industry. To achieve our goals we are working closely with local Research & Enterprise and Business Development staff at Glasgow University, and the broader SUPA KT team, in establishing and maintaining collaborations with current and possible future beneficiaries and in the setting up and management of non-disclosure agreements and applications for patents. Thus we will ensure that future knowledge exchange opportunities are identified early and exploited fully.

Outreach to schools, science centres, museums and the general public is very strong in the field of Gravitational Wave research, driven by interest in viewing the Universe through the medium of gravity - probing black holes, the warping of space-time and the big bang itself. We have successfully engaged the wider community through numerous efforts. For example we presented the exhibit "Can you hear Black Holes" at the 2008 Royal Society Summer exhibition with related exhibits still on show in the Science Museum in London, following which we undertook a key role in the design and construction of the NSF-funded US exhibit "Astronomy's New Messengers" which featured at the World Science Festivals in 2009 and 2010 and then as a touring exhibit. With funding from STFC we developed "Gravity Beyond the Apple", an interactive secondary school science show delivered in conjunction with the award-winning "Science Made Simple" public outreach company based in Cardiff University. We also made a key contribution to the "100 Hours of Astronomy" IYA2009 cornerstone project, which featured live webcasts from all the ground-based gravitational wave observatories, and more recently have been very active in Star-Gazing Live.

In the future we will maintain and extend our programme of public engagement, through our existing network of relationships with key outreach stakeholders, which includes: science centres and museums, national education authorities, the amateur astronomical community, the media and professional science communicators - particularly Wendy Sadler, director of "Science Made Simple" and the science team at the Glasgow Science Centre. Among our specific plans we will deliver across the UK numerous interactive lectures to schools, astronomical societies and the general public, in the areas of gravitational wave detection, cosmology and multi-messenger astronomy, drawing upon the suite of themed lectures which we have already developed.