Long-term general relativistic magnetohydrodynamics simulations of magnetic field in isolated neutron stars

Abstract

Strong magnetic fields play an important role in powering the emission of neutron stars. Nevertheless, a full understanding of the interior configuration of the field remains elusive. In this work, we present General Relativistic MagnetoHydroDynamics simulations of the magnetic field evolution in neutron stars lasting ∼880 ms (∼6.5 Alfvé n crossing periods) and up to resolutions of 0.1155 km using Athena++. We explore two different initial conditions, one with purely poloidal magnetic field and the other with a dominant toroidal component, and study the poloidal and toroidal field energies, the growth times of the various instability-driven oscillation modes and turbulence. We find that the purely poloidal setup generates a toroidal field which later decays exponentially reaching $1{{\ \rm per\ cent}}$ of the total magnetic energy, showing no evidence of reaching equilibrium. The initially stronger toroidal field setup, on the other hand, loses up to 20 per cent of toroidal energy and maintains this state till the end of our simulation. We also explore the hypothesis, drawn from previous MHD simulations, that turbulence plays an important role in the quasi equilibrium state. An analysis of the spectra in our higher resolution setups reveal, however, that in most cases we are not observing turbulence at small scales, but rather a noisy velocity field inside the star. We also observe that the majority of the magnetic energy gets dissipated as heat increasing the internal energy of the star, while a small fraction gets radiated away as electromagnetic radiation.

Gravitational-wave evolution of newborn magnetars with different deformed structure

“…On the contrary, within the relativistic MHD simulation, Ref. [46] shows that the Λ would stabilize at an equilibrium value of 0.2 when the toroidal initial setup dominated. The timescale from instability to approximately stability (< 1 s) is much shorter than the timescale we consider, so we ignore the evolution of Λ in the following calculations.…”

“…3. From the MHD simulation point of view, for given different initial magnetic field configurations, Λ is as large as 0.8 in a relativistic situation, but in a Newtonian simulation, the Λ would stabilize at an equilibrium value of 0.2 [45,46]. So, we choose Λ = 0.2, 0.35, 0.8 in our calculations.…”

Wave Phenomena In General Relativistic Magnetohydrodynamics

“…Usually, in GRMHD numerical studies, the ideal magnetohydrodynamics limit ( large magnetic Reynolds number) is used, and other dissipative effects (due to bulk and shear viscosity, etc.) are usually neglected [4,[6][7][8][9]. The ideal-MHD (note that we use "ideal" to denote large electrical conductivity, and zero or vanishing viscosity is termed as non-viscous fluid to avoid confusion) might be a good approximation for large celestial bodies where the length scale involved is large, and gradients are small [10,11].…”

An Extension of Gmunu: General-relativistic Resistive Magnetohydrodynamics Based on Staggered-meshed Constrained Transport with Elliptic Cleaning

“…Progress on the development of robust and accurate numerical codes for solving ideal relativistic MHD systems has been achieved in recent years (e.g., Komissarov 1999;Balsara 2001;Del Zanna & Bucciantini 2002;Gammie et al 2003;Anninos et al 2005;Mignone & Bodo 2006;Giacomazzo & Rezzolla 2006;Del Zanna et al 2007;Mignone et al 2009;White et al 2016;Porth et al 2017;Olivares et al 2019;Ripperda et al 2019;Liska et al 2019;Mewes et al 2020;Cipolletta et al 2020). In addition, these relativistic MHD codes have been successfully applied in studies of gamma-ray bursts and relativistic jets (McKinney & Blandford 2009;Mimica et al 2009;Mignone et al 2010;Mizuno et al 2015;Bodo et al 2016;Rossi et al 2017;Bromberg et al 2018;Nathanail et al 2019), accretion flows (McKinney et al 2012;Mukherjee et al 2013;Mizuno et al 2018), magnetized relativistic stars (Zink et al 2007;Lasky et al 2012;Lasky & Melatos 2013;Sur et al 2022), and tidal disruption events (Sądowski et al 2016;Anninos et al 2018;Dai et al 2018).…”