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.