Investigations in Gravitational Radiation

Einstein's General Relativity predicts that dynamical systems in strong gravity fields will emit vast amounts of energy in the form of gravitational waves (GW). Thse ripples in the very fabric of spacetime that travel from their sources at the speed of light, carrying information about physical processes responsible for their emission. 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 sensitivities where detection is expected within a few years.

The worldwide network of interferometric detectors includes the American advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO), the French-Italian-Dutch-Polish advanced Virgo (AdV) and the German-UK GEO600 that are being enhanced with a new detector (KAGRA) under construction 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 has enabled continuous data acquisition, with sensitivity to a wide range of sources and phenomena, over most of the sky. Modelling GW sources has allowed deeper searches and data from LIGO, Virgo, and GEO have increased our understanding of astronomical phenomena. For example, we have built accurate models to describe the dynamics of spinning black hole binaries for improving efficiency of detection and accuracy of parameter estimation, initiated studies on distinguishing models of the formation and evolution of compact binaries and supernovae, ruled out merging neutron star binary as progenitor of the gamma ray burst (GRB) GRB070201, and shown that less than 1% of the Crab pulsar's radiated power is in GW.

We are now entering a new era as advanced detectors begin their first phase of operation and within a few years will, we expect, routinely observe GW. The aLIGO detectors are based on the quasi-monolithic silica suspension concept developed in the UK for GEO600 and on the high power lasers developed by our German colleagues in GEO600. The AdV also uses a variant of the silica suspension technology. Further, KAGRA is being built with input on cryogenic bonding technology from the UK groups.

The consortium groups have initiated and led searches for astronomical sources, thanks to funding support received since first data taking runs began 12 years ago. Key ingredients of several searches (accurate waveforms models, geometric formulation of data analysis to optimise searches, algorithms to search for generic bursts, Bayesian search and inference techniques) were developed at Cardiff and Glasgow.

We propose a programme that leads to full exploitation of data from aLIGO and AdV, building on the analysis of data from the most recent LIGO/Virgo science runs and from GEO600 while the advanced detectors were under construction. In particular, we will refine waveform models and carry out deep and wide parameter space searches for coalescing binaries, GW emitted in coincidence with GRBs and supernovae, and continuous signals from rotating neutron stars.

In parallel, we propose essential detector R&D. 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, essential to maximize the astrophysical potential of GW observatories. We have major responsibilities for the silica suspensions in aLIGO, both in the US and for a possible 3rd aLIGO detector in India, and in the development of enhancements and upgrades to the aLIGO detectors in the areas of mirror coatings for low thermal noise, silicon substrates, room temperature and cryogenic suspensions and improved interferometer topologies to combat quantum noise.

The consortium has a strong and extensive track record in working with industry, in public outreach and schoolteacher CPD, which will continue under the proposed work. Beneficiaries will include the optics industry e.g. companies such as Gooch and Housego (enhancing capability in the area of manufacture of optical components), and such as Gas Sensing Solutions via development of custom optical filters for medical applications. Beneficiaries will also include those working in the sectors of energy/security via the application of MEMS gravimeters. The consortium has transferred technical knowledge and will further do so to help company competitiveness and success, all feeding back into the UK economy. The UK economy will further benefit through the spinning off of new companies arising from the research - based on a combination of the experience of the consortium members e.g. those at UWS who have already spun-off four companies and are in the midst of spinning off two others - and younger members at Glasgow and Sheffield who are heading to spin off their first company or license out their technology.

We anticipate research developments, spinning off from the gravitational wave work to contribute to the grand challenge areas of health and wellbeing via developments of software algorithms which can help with removal of artefacts in scanning medical imaging devices. More globally, as a spin-off from the gravitational waves work at Cardiff a Data Innovation Institute has been established to conduct fundamental research into the aspects of managing, analysing and interpreting massive volumes of textual and numerical information. This will benefit projects a wide-ranging spectrum of disciplines including social, biological, life and engineering sciences. For example, in the biological and life sciences by extracting information from data sets without compromising privacy and confidentiality, and interpreting large data sets into reliable and understandable mathematical models.

Public outreach involving television, radio, science festivals, masterclasses and public lectures feature strongly in our present and proposed programmes and the legacy of the effort we have devoted to celebrate the international year of light - such as the development of a laser harp - fit well with the wider public outreach work we undertake in collaboration with the LIGO Scientific Collaboration on the physics of neutron stars, black holes and the Universe as a whole.

Working with the Scottish government and Education Scotland members of the consortium will build on previous work contributing strongly to the curriculum for physics in Scotland by extending provision of CPD for schoolteachers in Scotland, producing videos and other material helping them to tackle the challenges introduced by the more interdisciplinary nature of the new school qualifications, and this support is very transportable to be used throughout the UK.

The wide range of impact provided by the scale of our programme is excellent for the training of early career researchers and graduate students and we aim to ensure that all our young scientists have experience in these areas, enabling them to have access to a wide range of career opportunities.