Collaborative Research: Petascale Simulations of Binary Neutron Star Mergers

Philipp Moesta, University of California, Berkeley

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Erik Schnetter, Roland Haas, Philipp Moesta, David Radice, Goni Halevi, Andre da Silva Schneider, Jose Arredondo, Francesco Zappa, Nestor Ortiz Madrigal, Vsevolod Nedora

The era of multimessenger astronomy has been inaugurated with the extraordinary detection of the collision of two neutron stars (NSs) by the Laser Interferometer Gravitational-Wave Observatory (LIGO), and the subsequent observations by X-ray, optical, infrared, and radio facilities. These observations have started to revolutionize our understanding of many areas in physics, including the origins of the heavy elements, like silver, gold, and platinum. However, they also pose many pressing open questions. This project will make use of the Blue Waters supercomputer to address these open questions. State-of-the-art NS merger simulations will be performed on the Blue Waters supercomputer to examine all the different possible NS collision scenarios to understand the fundamental physical processes that generated the observation data. This will be followed by extremely high-resolution simulations considering the post-merger evolution. Simulation results will be made publicly available, and dissemination via movies, public lectures and school visits are planned.

A systematic study of the evolution of NS binary systems compatible with the observed NS collision, GW170817, will be performed by means of merger simulations on Blue Waters, employing sophisticated microphysics and neutrino treatment. These simulations will ascertain the viability of tidal torques and shocks as mechanisms for the ejection of matter during mergers, which in turn powers the observed optical and infrared transients and synthesizes heavy elements. The impact of the NS equation of state (EOS) will be evaluated by considering a set of 3 EOSs spanning the range of the current nuclear uncertainties. The range of possible outcomes of the merger as a function of the binary parameters and EOSs will be assessed. High-resolution general-relativistic magnetohydrodynamics simulations of the merger remnant will be performed, with sufficient resolution to determine the magnetorotational instability (MRI) and the angular-momentum redistribution in the remnant while employing a microphysical treatment of the NS matter. These simulation results will ascertain the role of magnetohydrodynamics processes in determining the lifetime of the remnant and the observational signatures of an early or delayed black-hole formation. The role played by magnetized winds in the powering of the optical and infrared emissions and their nucleosynthetic yields will be assessed. In addition, this project will develop significant improvements to current open-source codes, and all improvements will be released to the community.