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Numerical modelling of gravitational wave sources in general relativity



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The first direct detection of gravitational waves (GWs) from a black-hole (BH) binary, GW150914, by the advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) detectors in 2015 heralded a new era in GW physics. Since then, over 90 compact binary merger events have been detected by the GW detector network with many more expected in the decades to come. A significant part of the theoretical foundations that underpins this achievement is the modelling of GW sources in General Relativity (GR) using numerical relativity (NR). In this thesis, we discuss the features and capabilities of the NR code GRChombo. Although GRChombo is no longer a new code, its original development and design targeted applications beyond the conventional astrophysical paradigm that other NR codes have focussed on. Here, we describe more recent additions that have allowed GRChombo to model BH binaries and other GW sources with good accuracy. Through direct comparison, we demonstrate that this accuracy is comparable to that of a more mature NR code. One of the key capabilities of GRChombo is its adaptive mesh refinement (AMR). This allows the numerical grid to dynamically adjust itself in order to sufficiently resolve the large range of spatial and temporal scales that characteristically arise in non-trivial solutions of GR as a consequence of the theory’s non-linearity. However, this flexibility requires careful control in order to achieve the desired accuracy and we discuss in detail the lessons learned in order to achieve this with GRChombo. We apply GRChombo and these techniques to the investigation of the effect of orbital eccentricity on the GW emission and the gravitational recoil imparted to the BH merger remnant from the inspiral and merger of unequal-mass non-spinning BH binaries. Finally, we explore the modelling of a more exotic type of compact object: boson stars (BSs) which are comprised of complex scalar field matter. In particular, we investigate the construction of suitable initial data describing BS binaries and its effect on the ensuing evolutions.





Sperhake, Ulrich


General Relativity, Gravitational Waves, Numerical Relativity, Theoretical Physics


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
STFC (1936371)
Science and Technology Facilities Council (1936371)
European Commission Horizon 2020 (H2020) Marie Sk?odowska-Curie actions (690904)
Science and Technology Facilities Council (ST/R00689X/1)
Science and Technology Facilities Council (ST/P000673/1)
STFC (via University of Leicester) (ST/R002452/1)