When two neutron stars collide, the resulting gravitational waves and light signals carry information about the most extreme physics in the universe—but current models cannot decode that information with enough precision. This project builds a new set of theoretical tools to extract those signals accurately. The researchers will develop a general relativistic radiative transport (GRRT) formulation and numerical codes that can simulate how light and particles move through the violently changing gravitational fields around merging black holes and neutron stars. If successful, the work will allow astronomers to use gravitational wave data to study phenomena that cannot be recreated in any laboratory, such as the spin-curvature coupling in extreme-mass-ratio binaries and the quantum chromodynamics phase transition during neutron star mergers. The codes will be made public, enabling the wider community to compute high-precision pulsed radiation from millisecond pulsars orbiting black holes and to determine the electromagnetic signatures when a binary neutron star merger collapses into a black hole. This is fundamental science: it will not change everyday life directly, but it will transform how we read the universe’s most violent events.
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The discovery of electromagnetic (EM) counterparts of the gravitational wave (GW) source GW170817 has opened up new opportunities for exploring the energetic Universe with multi-messenger astronomy. This project aims to provide a reliable theoretical toolset for exploitation of the rich information in high-precision EM/particle observational data of GW sources. The objective is to advance our understanding of fundamental physics phenomena that are not replicable in laboratories, such as, dynamics and spin-curvature coupling in extreme-mass-ratio binaries (EMRB), and black-hole (BH) formation and QCD phase transition in binary neutron-star (NS) mergers. We will construct a new general relativistic radiative transport (GRRT) formulation and derive solution schemes for solving the GRRT equations to accurately determine the EM/particle signals from GW sources. We anticipate (i) a generalised covariant formulation, in Hamilton-Jacobi (HJ) form, for EM/particle transport in non-stationary gravitational fields, (ii) a new adaptive ray-tracing code and a new level-set code, that take advantage of excellent numerical accuracy in the symplectic scheme for solving the HJ-form GRRT equations, and (iii) a GRRT code for computing high-precision pulsed radiation from EMRB containing a millisecond pulsar, and (iv) a GRRT code for computing the EM/particle signals from the core region of binary NS mergers in the final stage. The impacts of this work include: make possible (1) to compute EM/particle signals with accuracy sufficient for fully utilisimg the high-precision multi-messenger data of GW sources, (2) to conduct proper GRRT of EM/particle in modulating gravitational fields, (3) to use EM information in GW template construction for EMRB in the presence of GW self-force, and (4) to determine the EM/particle signatures when a binary NS merger is collapsing into a BH. This work will take us to the next level of precision GRRT calculations in strong gravity and to a new paradigm of precision quantitative multi-messenger theoretical astrophysics. Wu/Younsi/Zane are world leading RT researchers, with proven track records on producing high-calibre, ground-breaking works in high-energy and relativistic astrophysics of NS and BH systems. The UCL-MSSL team is perhaps the strongest internationally for undertaking this project, as all necessary technical skills and expertises are in-house, from laying-down of mathematical foundation, construction of GRRT formulation, derivation of GRRT equations, development of numerical algorithms and solution schemes, and applications in real astrophysical systems, in addition to solid in-field knowledge and vast hand-on experience in high-energy and relativistic astrophysics, GW astrophysics, and particle/nuclear astrophysics. All codes will be made public.
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