General Relativistic Astrophysics

We are entering an era of high-precision astronomy, both electromagnetic and gravitational. The first generation of highly sensitive gravitational-wave detectors have reached design sensitivity and are being upgraded using advanced technology. LOFAR is on-line, providing significant improvements in radio timing precision. Future advances associated with the SKA in radio, the Einstein Telescope and the space based detector eLISA for gravitational waves will complement current quality X-ray observations, and will allow us to improve our understanding of the Universe significantly. To benefit maximally from these improvements, we need to improve our current models of a range of phenomena involving compact objects. Better quality theory is needed both to detect the various signals and to probe as much of the relevant physics as possible.

This research proposal builds on the Southampton Gravity Group's expertise in black hole, neutron star and gravitational-wave astrophysics, and is aimed at developing a deeper understanding of the dynamics of black holes and neutron stars, the associated observational signatures and how these signals can be used to provide information about the involved physics. The programme is of a highly interconnected nature with four different themes requiring similar methodology (e.g. general relativistic perturbation theory or numerical simulations) and physics input (e.g. superfluidity, magnetic fields or gravitational radiation reaction). The overall aim is to develop significantly improved models that can be tested against future high-precision observations in a range of channels.

Neutron stars are unique astrophysical laboratories, the modelling of which requires much poorly known physics. In order to investigate their properties, one must combine supranuclear physics with magnetohydrodynamics, a description of superfluids and superconductors, potentially exotic phases of matter like a deconfined quark-gluon plasma and, of course, general relativity. Achieving a better understanding of neutron star dynamics is one of the key aims of this proposal. We will carry out three projects, focused on the dynamics and evolution of neutron stars. The proposed work is of immediate relevance for gravitational-wave physics, leading to astrophysically motivated signal searches, and provides useful insights into problems relevant for electromagnetic observations. We aim to construct accurate models of neutron star dynamics that can be tested against recent observations of oscillations associated with magnetar giant flares, and which will inform future targeted searches for r-mode oscillations in fast spinning neutron stars. We will provide improved models of the enigmatic glitches and other timing phenomena seen in radio pulsars. We also plan to carry out nonlinear simulations of neutron star mergers with an unprecedented level of realism, exploring electromagnetic counterparts to the emerging gravitational waves.

Inspiralling binaries are intrinsically the strongest sources of gravitational waves in the Universe. Gravitational waveforms from such events are extremely efficient probes of the strong gravity near black holes, and their detection promises to allow accurate tests of gravitational theory in its most extreme domain. In order to realise this promise we need a good theoretical understanding of relativistic radiation-reaction effects. Recent progress on the problem of the gravitational self-force provides significant momentum for work in this area. Building on this, we will explore the promising synergy between self-force calculations, numerical relativity and post-Newtonian theory, in order to inform a universal model of binary inspirals across the entire range of mass ratios and spin rates.

This summary identifies some of the routes by which our astrophysics research programme will impact upon the wider world, including the general public, other scientific disciplines, and the technology sector.

COMMUNICATIONS AND ENGAGEMENT: The Southampton Gravity Group has a consistent track record of engaging with the public to communicate the latest and most exciting aspects of its research. These have included public talks, lectures to school students, coordination of a Royal Society Summer Exhibition and contact with Members of Parliament. The Group plans to enhance this activity, with STFC-funded researchers playing a leading role in exploring new dissemination outlets, including "Meet the Astronomer" sessions and the construction of interview/video clips for electronic circulation. The most exciting research advances will be promoted via the University Press office, whose help in publicising recent breakthroughs played a role in several articles on Southampton research appearing in the press, including in National Geographic, New Scientist and The Daily Mail.

COLLABORATION: The richness of the physics needed to model compact objects naturally leads to the possibility of developing collaborations with traditionally disparate scientific disciplines. In particular, there is scope for collaboration with experts in low-temperature physics, whose knowledge of condensed matter many prove invaluable in understanding neutron star interiors. Equally exciting is the possibility of exploiting links between the black hole inspiral problem and the problem of nonlinear electromagnetic pulse propagation in an optical fibre. Steps will be taken to explore these exciting overlaps, which will include the organisation of focused study groups to explore the key issues.

EXPLOITATION AND APPLICATION: The theoretical work of the Group is intimately linked to several large experimental efforts, whose innovative technological development impacts on industry, with spin-offs including satellite stabilisation systems, seismic isolation, the construction of large vacuum cavities, and laser stabilisation. As well as providing motivation for these efforts, the theoretical modelling of the Group is crucial in making informed decisions as to how changes in expenditure and project duration impact on science capabilities.

CAPABILITY AND RESOURCE: We are rapidly approaching an era of precision astronomy, with new electromagnetic and gravitational experimental projects under rapid development. The young researchers that the Group hopes to recruit will receive training in exploiting these opportunities that few other groups could provide. Previous Group members have already gone on to secure prestigious academic appointments. Beyond the world of academia, the skill sets that the researchers would acquire would also equip them to play important roles in the wider community, as is reflected in the success of previous members in gaining attractive jobs in industry. The University recently established a Research Development and Graduate Centre that will help systematize this training, and enable the Group to continue to produce well-rounded researchers with skills well suited to demands of the 21st Century economy and academia.