Radiation in neutron star merger remnant simulations

Abstract

Binary neutron star mergers are extreme astrophysical events. They involve mass densities multiple times greater than that of an atomic nucleus, velocities nearing half the speed of light, temperatures soaring up to 100 billion Kelvin, and gravitational acceleration reaching up to 100 billion times that at the Earth's surface. The binary neutron star merger known as GW170817 marked a pivotal moment as the first observation of a gravitational wave with an electromagnetic counterpart. The complete evolution and dynamics of neutron star merger remnants remain not fully understood, underscoring the need for further research. Investigation of these events holds the potential to refine both our theories of gravity and our understanding of the properties of matter at extreme densities and temperatures.

Numerical simulations are an appropriate tool to approach an understanding of these complex processes. By employing such simulations, we can explore which physical approximations and numerical techniques are sufficient to capture the range of behaviours involved. However, binary neutron star merger remnants present a formidable computational challenge due to the vast range of length scales involved and the system of highly non-linear coupled partial differential equations governing mass, momentum, and energy evolution.

Addressing this challenge, this project has involved the creation of a novel three-dimensional physics code capable of simulating hydrodynamic evolution, radiative transfer, and the general relativistic effects induced by fluid motion and spacetime curvature. This code has been implemented into the AMReX software framework to make use of block-structured adaptive mesh refinement for enhanced accuracy and efficiency.

In this thesis, I present state-of-the-art simulations of binary neutron star merger remnants. Making use of a pre-calculated merger simulation generated using the Einstein Toolkit and employing a tabulated physical equation of state. We find that the introduction of a radiation field can disperse material surrounding a remnant object, and that coordinate transforms can help reduce numerical advective flux errors. Additionally, I utilize this code to explore uncertainty quantification by modelling turbulent simulations and analysing the convergence of statistical solutions.

More information

Identifiers

ORCID for Grant Schomberg: orcid.org/0009-0003-3407-2854

ORCID for Ian Hawke: orcid.org/0000-0003-4805-0309

ORCID for Ralf Deiterding: orcid.org/0000-0003-4776-8183

Catalogue record

Export record