The physics of non-ideal general relativistic magnetohydrodynamics

Andersson, Nils; Hawke, Ian; Celora, Thomas; Comer, G. L.

doi:10.1093/mnras/stab3257

Cited by 6 publications

(2 citation statements)

References 34 publications

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“…Finally, our initial magnetic field configuration neglects the external magnetosphere and large-scale fields likely present in the inspiral phase of a BNS system. Simulating regions of extremely high magnetic pressure in ideal MHD is challenging; various strategies have been pursued, such as imposing highdensity atmospheres (Paschalidis et al 2015;Ruiz et al 2016) to reduce the plasma β parameter and to maintain stability, improving the conservative-to-primitive scheme , or using nonideal (resistitive) MHD approximations (Andersson et al 2022). Our conservative-to-primitive scheme has already been significantly optimized to handle large plasma-β.…”

Section: Models: Eos and Initial Datamentioning

confidence: 99%

GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process Nucleosynthesis and Electromagnetic Signatures of Dynamical Ejecta

Combi

Siegel

2023

ApJ

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Fast neutron-rich material ejected dynamically over ≲10 ms during the merger of a binary neutron star (BNS) can give rise to distinctive electromagnetic counterparts to the system’s gravitational-wave emission that serve as a “smoking gun” to distinguish between a BNS and an NS–black hole merger. We present novel ab initio modeling of the kilonova precursor and kilonova afterglow based on 3D general-relativistic magnetohydrodynamic simulations of BNS mergers with nuclear, tabulated, finite-temperature equations of state (EOSs), weak interactions, and approximate neutrino transport. We analyze dynamical mass ejection from 1.35–1.35 M ⊙ binaries, consistent with properties of the first observed BNS merger GW170817, using three nuclear EOSs that span the range of allowed compactness of 1.35 M ⊙-neutron stars. Nuclear reaction network calculations yield a robust second-to-third-peak r-process. We find few ×10−6 M ⊙ of fast (v > 0.6c) ejecta that give rise to broadband synchrotron emission on ∼years timescales, consistent with tentative evidence for excess X-ray/radio emission following GW170817. We find ≈2 × 10−5 M ⊙ of free neutrons that power a kilonova precursor on ≲ hours timescale. A boost in early UV/optical brightness by a factor of a few due to previously neglected relativistic effects, with enhancements up to ≲10 hr post-merger, is promising for future detection with UV/optical telescopes like Swift or ULTRASAT. We find that a recently predicted opacity boost due to highly ionized lanthanides at ≳70,000 K is unlikely to affect the early kilonova based on the obtained ejecta structures. Azimuthal inhomogeneities in dynamical ejecta composition for soft EOSs found here (“lanthanide/actinide pockets”) may have observable consequences for both early kilonova and late-time nebular emission.

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Section: Models: Eos and Initial Datamentioning

confidence: 99%

GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process Nucleosynthesis and Electromagnetic Signatures of Dynamical Ejecta

Combi

Siegel

2023

ApJ

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“…Therefore, the u a /c and ⊥ b a projections of the Maxwell equations and the continuity equation are [34]…”

Section: The 3 + 1 Field Equationsmentioning

confidence: 99%

A Variational Approach to Resistive General Relativistic Two-Temperature Plasmas

et al. 2023

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We develop an action principle to construct the field equations for dissipative/resistive general relativistic two-temperature plasmas, including a neutrally charged component. The total action is a combination of four pieces: an action for a multifluid/plasma system with dissipation/resistivity and entrainment; the Maxwell action for the electromagnetic field; the Coulomb action with a minimal coupling of the four-potential to the charged fluxes; and the Einstein–Hilbert action for gravity (with the metric being minimally coupled to the other action pieces). We use a pull-back formalism from spacetime to abstract matter spaces to build unconstrained variations for the neutral, positively, and negatively charged fluid species and for three associated entropy flows. The full suite of field equations is recast in the so-called “3+1” form (suitable for numerical simulations), where spacetime is broken up into a foliation of spacelike hypersurfaces and a prescribed “flow-of-time”. A previously constructed phenomenological model for the resistivity is updated to include the modified heat flow and the presence of a neutrally charged species. We impose baryon number and charge conservation as well as the Second Law of Thermodynamics in order to constrain the number of free parameters in the resistivity. Finally, we take the Newtonian limit of the “3+1” form of the field equations, which can be compared to existing non-relativistic formulations. Applications include main sequence stars, neutron star interiors, accretion disks, and the early universe.

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Modelling general-relativistic plasmas with collisionless moments and dissipative two-fluid magnetohydrodynamics

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Noronha

Philippov

2022

Monthly Notices of the Royal Astronomical Society

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Relativistic plasmas are central to the study of black hole accretion, jet physics, neutron star mergers, and compact object magnetospheres. Despite the need to accurately capture the dynamics of these plasmas and the implications for relativistic transients, their fluid modeling is typically done using a number of (overly) simplifying assumptions, which do not hold in general. This is especially true when the mean free path in the plasma is large compared to the system size, and kinetic effects start to become important. Going beyond common approaches used in the literature, we describe a fully relativistic covariant 14-moment based two-fluid system appropriate for the study of electron-ion or electron-positron plasmas. This generalized Israel-Stewart-like system of equations of motion is obtained directly from the relativistic Boltzmann-Vlasov equation. This new formulation can account for non-ideal effects, such as anisotropic pressures and heat fluxes, not present in previous formulations of two-fluid magnetohydrodynamics. We show that a relativistic two-fluid plasma can be recast as a single fluid coupled to electromagnetic fields with (potentially large) out-of-equilibrium corrections. We keep all electron degrees of freedom, which provide self-consistent evolution equations for electron temperature and momentum. The out-of-equilibrium corrections take the form of a collisional 14-moment closure previously described in the context of viscous single fluids. The equations outlined in this paper are able to capture the full two-fluid character of collisionless plasmas found in black hole accretion and flaring processes around compact objects, as well Braginskii-like two-fluid magnetohydrodynamics applicable to weakly collisional plasmas inside accretion disks.

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The physics of non-ideal general relativistic magnetohydrodynamics

Cited by 6 publications

References 34 publications

GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process Nucleosynthesis and Electromagnetic Signatures of Dynamical Ejecta

GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process Nucleosynthesis and Electromagnetic Signatures of Dynamical Ejecta

A Variational Approach to Resistive General Relativistic Two-Temperature Plasmas

Modelling general-relativistic plasmas with collisionless moments and dissipative two-fluid magnetohydrodynamics

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