Modelling compact objects for precision astrophysics

Lead Research Organisation: University of Southampton
Department Name: School of Mathematics

Abstract

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 LISA 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 advances, 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 General Relativity Group's expertise in black hole, neutron star and gravitational wave astrophysics, and is aimed at developing a deeper understanding of the dynamics of compact objects, the associated observational signatures and how signals can be used to probe the underlying physics. The programme is of a highly interconnected nature with three 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 two parallel projects, focused on neutron star dynamics and relevant astrophysical scenarios. 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 pulsations that can be tested against recent observations of oscillations associated with magnetar giant flares, and which will inform future targeted gravitational-wave 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 account for environmental effects, e.g., the role of the magnetosphere in the context of intermittent pulsars and effects due to variable torques in accreting systems relevant for X-ray timing observations.

Inspiralling binaries are intrinsically the strongest sources of gravitational waves in the Universe. In particular, there are exciting prospects for LISA to detect the radiative inspiral of compact objects into massive black holes in galactic centres. Gravitational waveforms from such events are extremely efficient probes of the strong gravity near the massive black hole, and promise 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.

Planned Impact

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 Relativity 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 recent 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 the formal links between aspects of the black hole inspiral problem and other problems in applied mathematics, notably the problem of nonlinear electrodynamics in media with non-uniform dispersion (of importance in fibre optics) which bares a striking resemblance to the EMRI problem in its mathematical formulation. 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 in 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 offer. 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.

Publications

10 25 50
 
Description Contributed key findings supporting searches for gravitational waves.
Exploitation Route Continued research.
Sectors Education

 
Description Marie Curie Fellowships
Amount £250,000 (GBP)
Organisation Spanish National Research Council (CSIC) 
Sector Public
Country Spain
Start 10/2013 
End 09/2016
 
Description Rubicon Fellowship
Amount € 164,000 (EUR)
Organisation Netherlands Organisation for Scientific Research (NWO) 
Sector Public
Country Netherlands
Start 04/2013 
End 03/2015
 
Description Starting grants
Amount € 1,459,268 (EUR)
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 09/2012 
End 08/2017