Dynamically Stable Magnetic Fields in Relativistic Neutron Stars: A Diverse Landscape of GRMHD Equilibria
Year: 2026
Type: preprint
Abstract: Neutron stars endowed with purely poloidal or purely toroidal magnetic fields are known to be unstable, and settle into mixed poloidal-toroidal configurations. The end state of these instabilities is still poorly understood. It is unclear whether this state is unique or whether the dynamically stable configuration has memory of the initial conditions. In this work, we perform long-term, fully general relativistic magnetohydrodynamic simulations of equilibrium configurations of slowly rotating neutron stars endowed with self-consistent mixed poloidal and toroidal magnetic fields. Our initial configurations differ in their initial magnetization and magnetic field geometry. We evolve the initial equilibria for tens of Alfvén timescales until well after any instabilities have saturated. Employing an array of diagnostic tools from visualizations to the structure of the plasma four-current and a vector spherical harmonic decomposition of the settled magnetic fields, we characterize the structure of the dynamically stable, settled magnetic equilibria. We find that the settled configurations are not unique. Instead, they exhibit diverse multipolar structures, with higher-order modes contributing substantially. Our findings demonstrate that there is memory of the magnetic-field initial conditions, and that there is no unique dynamically stable magnetic-field geometry for neutron stars. Nevertheless, we find that the angle-averaged radial profile of the magnetic field toroidal to poloidal amplitude in the bulk of the settled configurations exhibits some degree of universality with typical values of order \(20\)--\(40\%\).
Source: arXiv (Cornell University)
Institutions: University of Arizona, University of the Ryukyus
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, National Aeronautics and Space Administration, Aspen Center for Physics, National Centre for Supercomputing Applications, University of the Ryukyus, University of Illinois at Urbana-Champaign, Japan Society for the Promotion of Science, Office of Advanced Cyberinfrastructure
Awards: G1353381076, G1453181110, Construction of various initial data for numerical relativity simulations, G1503004319, Track 4: Advanced CI Coordination Ecosystem: Monitoring and Measurement Services, A new approach for stability analysis of magnetized stars, G2595738051, G2848635288, G298330452, G3192771852, G3562386289, CAREER: Research in Strong-Field Gravity and Astrophysics, Elements: An initial value solver for the era of multi-messenger astrophysics, Track 1: ACCESS Resource Allocations Marketplace and Platform Services (RAMPS), G4010157413, G4403015908, G4458505638, ACO: An Open CI Ecosystem to Advance Scientific Discovery (OpenCI), Track 3: COre National Ecosystem for CyberinfrasTructure (CONECT), G5367127336, G5464919783, Initial data for numerical relativity simulations associated with standing waves, General relativistic equilibrium configurations of magnetized neutron stars, G6385132645, G6709186444, G6754955425, G7157392653, コンパクト連星の一般相対論的準平衡解における磁場構造, G7425678691, Programs on Critical Problems in Physics, Astrophysics and Biophysics at the Aspen Center for Physics, G8108599699, Track 2: Customized Multi-tier Assistance, Training, and Computational Help (MATCH) for End User ACCESS to CI, Theoretical Studies in Gravitation and Astrophysics, G8562358136, Quasi-equilibrium binary neutron stars with magnetic fields and internal structure in general relativity, G8753591634, G8851268641
OpenAlex ID: W7214395397