Crustal Magnetic Fields Do Not Lead to Large Magnetic-field Amplifications in Binary Neutron Star Mergers

Creators: Chabanov, Michail; Tootle, Samuel D.; Most, Elias R.; Rezzolla, Luciano

Abstract

The amplification of magnetic fields plays an important role in explaining numerous astrophysical phenomena associated with binary neutron star mergers, such as mass ejection and the powering of short gamma-ray bursts. Magnetic fields in isolated neutron stars are often assumed to be confined to a small region near the stellar surface, while they are normally taken to fill the whole star in numerical modeling of mergers. By performing high-resolution, global, and high-order general-relativistic magnetohydrodynamic simulations, we investigate the impact of a purely crustal magnetic field and contrast it with the standard configuration consisting of a dipolar magnetic field with the same magnetic energy but filling the whole star. While the crust configurations are very effective in generating strong magnetic fields during the Kelvin–Helmholtz-instability stage, they fail to achieve the same level of magnetic-field amplification of the full-star configurations. This is due to the lack of magnetized material in the neutron-star interiors to be used for further turbulent amplification and to the surface losses of highly magnetized matter in the crust configurations. Hence, the final magnetic energies in the two configurations differ by more than 1 order of magnitude. We briefly discuss the impact of these results on astrophysical observables and how they can be employed to deduce the magnetic topology in merging binaries.

Additional Information

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. We thank Vasilis Mpisketzis for useful discussions. Partial funding comes from the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt as part of the strategic R&D collaboration with Goethe University Frankfurt, from the State of Hesse within the Research Cluster ELEMENTS (Project ID 500/10.006), by the ERC Advanced Grant "JETSET: Launching, propagation and emission of relativistic jets from binary mergers and across mass scales" (grant No. 884631) and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the CRC-TR 211 "Strong-interaction matter under extreme conditions"–project number 315477589—TRR 211. L.R. acknowledges the Walter Greiner Gesellschaft zur Förderung der physikalischen Grundlagenforschung e.V. through the Carl W. Fueck Laureatus Chair. The simulations were performed on HPE Apollo HAWK at the High Performance Computing Center Stuttgart (HLRS) under the grant BNSMIC. E.R.M. gratefully acknowledges support as the John A. Wheeler Fellow at the Princeton Center for Theoretical Science, the Princeton Gravity Initiative and the Institute for Advanced Study. E.R.M. acknowledges support through the Extreme Science and Engineering Discovery Environment (XSEDE) through Expanse at SDSC and Bridges-2 at PSC through allocations PHY210053 and PHY210074. E.R.M. further acknowledges supported by Princeton Research Computing, a consortium of groups including the Princeton Institute for Computational Science and Engineering (PICSciE) and the Office of Information Technology's High Performance Computing Center and Visualization Laboratory at Princeton University. Software: Einstein Toolkit (Löffler et al. 2012), Carpet (Schnetter et al. 2004), FIL (Most et al. 2019), FUKA (Papenfort et al. 2021), Kadath (Grandclement 2010), CompOSE (https://compose.obspm.fr).

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