Abstract

While the landmark multimessenger observations associated with the binary neutron star (BNS) merger GW170817 confirmed the existence of merging BNS systems and their ability to generate gamma-ray bursts and kilonova emission, the exact physical processes that link hydrodynamics in the merger remnant to electromagnetic (EM) signals remains up for debate. Moreover, the uncertain lifetime of the remnant before its possible collapse to a black hole can dramatically change the physics involved in the postmerger evolution. We aim to facilitate and study energetic outflow launching in the long-lived hypermassive or supramassive neutron star remnant case by performing 3D general relativistic magnetohydrodynamics (GRMHD) simulations of a BNS merger featuring a novel low density atmosphere prescription and intentional saturation the postmerger EM energy. We report progress on including complex multiphysics models into a consistent simulation framework: the extension of tabulated microphysical equations of state (EOS) to low densities, use of the EOS in accurately solving the constraint equations of numerical relativity to generate BNS initial data, and EOS coupling to neutrino transport in the \texttt{IllinoisGRMHD} code. We demonstrate the capabilities of this framework in simulating the merger of an equal mass (1.35 solar mass), irrotational BNS from inspiral to 30 ms postmerger, where it survives as a long-lived remnant. In this time, the violent merger process heats the system to a temperature of 94 MeV and ejects 4.8e-3 solar masses of neutron-rich material consistent with r-process nucleosynthesis and later kilonova emission. The remnant efficiently amplifies the initial magnetic energy of 5e49 erg to 1e51 erg via turbulent motion at merger and later MHD processes in the accretion disk, potentially driving a relativistic polar outflow and gamma-ray emission. Finally, we discuss future applications of this framework to a wider array of initial binary parameters, including varying the mass ratio and NS spin, and potential improvements to the neutrino radiation and magnetic field prescriptions.

Publication Date

8-2024

Document Type

Thesis

Student Type

Graduate

Degree Name

Astrophysical Sciences and Technology (MS)

Department, Program, or Center

Physics and Astronomy, School of

College

College of Science

Advisor

Manuela Campanelli

Advisor/Committee Member

Richard O'Shaughnessy

Advisor/Committee Member

Yosef Zlochower

Campus

RIT – Main Campus

Download

Share

COinS