Gravitational wave astronomy

The emergence of gravitational-wave astronomy is rapidly changing the astrophysics landscape. From the breakthrough detection of merging black holes in 2015 to the astonishing neutron-star binary event from August 2017 and the regular alerts sent out by the LIGO-Virgo Scientific collaboration during the current observing run, it is clear that the gravitational-wave universe is richer than one might have expected. The impact and discovery potential of this new area of astronomy is considerable. As the sensitivity of the gravitational-wave instruments improves, a broader range of sources should come within reach. Further unique events (like GW170817) associated with electromagnetic counterparts will help resolve long-standing mysteries ranging from the formation and evolution of compact binarysystems to the central engine of short gamma-ray bursts, from the details of matter under the extreme pressures of a neutron star core to the dynamics of black holes and (through kilonova signatures) the formation of heavy elements in the Universe.

In order to realise the science potential of current and future instruments, we need to refine our understanding of the relevant theory. This is true for both ground- and space-based detectors. As we prepare for the third generation of ground-based interferometers (like the Einstein Telescope or the Cosmic Explorer) we need more precise models for neutron star astrophysics, including reliable nonlinear simulations of merger events. Similarly, preparing for space-based observations of the low-frequency gravitational-wave sky following the LISA launch in the early 2030s, we have to improve our dynamical models of supermassive black holes. These are not distant plans; immediate progress on the theory is required to inform the design of both instruments and data analysis strategies.

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 five 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. The natural emphasis is on problems involving neutron stars and black holes. These
fascinating and enigmatic objects involve inspirational science and represent unique laboratories for the exploration of the extremes of physics.

Black-hole astrophysics impacts on a range of fundamental issues, from the nature of gravity to problems in cosmology, e.g., associated with structure formation in the early Universe. Meanwhile, neutron star observations allow us to probe the state of matter under extreme conditions, providing us with information which complements that gleaned from colliders like the Large Hadron Collider at CERN. The modelling of these highly relativistic systems involves a broad range of physics that is not accessible in the laboratory. As our observational capabilities improve, we are reaching the point where precise modelling is required both to interpret data and to facilitate the observations in the first place.

The proposed research programme represents a coherent effort to explore the astrophysics of black holes and neutron stars in order to improve our understanding of the fundamental laws of physics of the Universe and reveal how nature operates on scales where our current understanding breaks down, a theme that remains central to the STFC mission.

This summary identifies some of the routes by which our astrophysics research programme impacts 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, contributions to Royal Society Summer Exhibitions and contact with Members of Parliament. We plan to enhance this activity, with STFC-funded researchers playing a leading role in exploring the full range of dissemination outlets, including the development of original material for electronic media. The most exciting research advances will be promoted via the University Press office, whose help in publicising breakthroughs played a role in articles on Southampton research appearing in the press, including in National Geographic, New Scientist and national newspapers.

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. We intend to explore these exciting overlaps, by organising focused study groups to explore the key issues.

EXPLOITATION AND APPLICATION: The theoretical work of the group is intimately linked to 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 early career researchers that the group plans to recruit will receive training in exploiting these opportunities that few other groups could provide. Previous group researchers have already secured prestigious academic appointments (e.g. in Cambridge, Amsterdam and Warsaw). 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's Doctoral College helps systematize this training, and enables the group to continue to produce well-rounded researchers with skills well suited to demands of the 21st Century economy and academia.