Impact of Magnetic-field-driven Anisotropies on the Equation of State Probed in Neutron Star Mergers
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1.
California Institute of Technology
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2.
Kent State University
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3.
University of Coimbra
Abstract
Binary neutron star mergers can produce extreme magnetic fields, some of which can lead to strong magnetar-like remnants. While strong magnetic fields have been shown to affect the dynamics of outflows and angular momentum transport in the remnant, they can also crucially alter the properties of nuclear matter probed in the merger. In this work, we provide a first assessment of the latter, determining the strength of the pressure anisotropy caused by Landau-level quantization and the anomalous magnetic moment. To this end, we perform the first numerical relativity simulation with a magnetic polarization tensor and a magnetic-field-dependent equation of state using a new algorithm we present here, which also incorporates a mean-field dynamo model to control the magnetic field strength present in the merger remnant. Our results show that—in the most optimistic case—corrections to the anisotropy can be in excess of 10% and are potentially largest in the outer layers of the remnant. This work paves the way for a systematic investigation of these effects.
Copyright and License
© 2025. 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.
Acknowledgement
The authors are grateful for discussions with Constança Providência and Ira Wasserman. E.R.M. acknowledges support from NASA’s ATP program under grant 80NSSC24K1229 and by the National Science Foundation under grant No. PHY-2309210. The work of L.S. and H.P. was partially supported by national funds from FCT (Fundação para a Ciência e a Tecnologia, I.P, Portugal) under projects UIDB/04564/2020 and UIDP/04564/2020, with DOI identifiers 10.54499/UIDB/04564/2020 and 10.54499/UIDP/04564/2020, respectively, and project 2022.06460.PTDC with the associated DOI identifier 10.54499/2022.06460.PTDC. L.S. acknowledges the PhD grant 2021.08779.BD (FCT, Portugal). H.P. acknowledges the grant 2022.03966.CEECIND (FCT, Portugal) with DOI identifier 10.54499/2022.03966.CEECIND/CP1714/CT0004. V.D. acknowledges support from the Department of Energy under grant DE-SC0024700 and from the National Science Foundation under grants MUSES OAC-2103680 and NP3M PHY2116686. E.R.M. acknowledges the use of Delta at the National Center for Supercomputing Applications (NCSA) through allocation PHY210074 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program, which is supported by National Science Foundation grants #2138259, #2138286, #2138307, #2137603, and #2138296. Additional simulations were performed on the NSF Frontera supercomputer under grant AST21006. E.R.M. also acknowledges support through DOE NERSC supercomputer Perlmutter under grant m4575, which uses resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under contract No. DE-AC02-05CH11231 using NERSC award NP-ERCAP0028480.
Software References
EinsteinToolkit (F. Loffler et al. 2012), Frankfurt/IllinoisGRMHD (Z. B. Etienne et al. 2015; E. R. Most et al. 2019), FUKA (L. J. Papenfort et al. 2021), Kadath (P. Grandclement 2010), kuibit (G. Bozzola 2021), matplotlib (J. D. Hunter 2007), numpy (C. R. Harris et al. 2020), scipy (P. Virtanen et al. 2020).
Files
Most_2025_ApJL_989_L29.pdf
Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2506.21696 (arXiv)
Funding
- National Aeronautics and Space Administration
- 80NSSC24K1229
- National Science Foundation
- PHY-2309210
- Fundação para a Ciência e Tecnologia
- UIDB/04564/2020
- Fundação para a Ciência e Tecnologia
- UIDP/04564/2020
- Fundação para a Ciência e Tecnologia
- 2022.06460.PTDC
- Fundação para a Ciência e Tecnologia
- 2021.08779.BD
- Fundação para a Ciência e Tecnologia
- 2022.03966.CEECIND
- United States Department of Energy
- DE-SC0024700
- National Science Foundation
- OAC-2103680
- National Science Foundation
- PHY2116686
- United States Department of Energy
- DE-AC02-05CH11231
- National Energy Research Scientific Computing Center
- NP-ERCAP0028480
Dates
- Submitted
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2025-06-27
- Accepted
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2025-07-31
- Available
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2025-08-13Published
Caltech Custom Metadata
- Caltech groups
- Physics Department , Walter Burke Institute for Theoretical Physics , TAPIR , Astronomy Department , Division of Physics, Mathematics and Astronomy (PMA)
- Publication Status
- Published