Modelling magnetically deformed neutron stars

Haskell, B.; Samuelsson, Lars; Glampedakis, Kostas; Andersson, Nils

doi:10.1111/j.1365-2966.2008.12861.x

Cited by 210 publications

(292 citation statements)

References 30 publications

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“…(9)). This is the case considered in most explicit descriptions of neutron star magnetic fields so far (Tomimura & Eriguchi 2005;Yoshida et al 2006;Haskell et al 2008;Akgün & Wasserman 2008;Kiuchi & Kotake 2008).…”

Section: Force Balancementioning

confidence: 99%

“…which is often assumed to characterize stellar magnetic fields (Tomimura & Eriguchi 2005;Yoshida et al 2006;Haskell et al 2008;Akgün & Wasserman 2008;Kiuchi & Kotake 2008). We emphasize that, in all the stars of interest here, the fluid is not barotropic, but stably stratified, with stabilizing buoyancy forces much stronger than the Lorentz forces, so the magnetic equilibria are not required to satisfy Eq.…”

Section: Axially Symmetric Equilibriamentioning

confidence: 99%

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Stable magnetic equilibria and their evolution in the upper main sequence, white dwarfs, and neutron stars

Reisenegger

2009

A&A

112

141

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Context. Long-lived, large-scale magnetic field configurations exist in upper main sequence, white dwarf, and neutron stars. Externally, these fields have a strong dipolar component, while their internal structure and evolution are uncertain but highly relevant to several problems in stellar and high-energy astrophysics. Aims. We discuss the main properties expected for the stable magnetic configurations in these stars from physical arguments and the ways these properties may determine the modes of decay of these configurations. Methods. We explain and emphasize the likely importance of the non-barotropic, stable stratification of matter in all these stars (due to entropy gradients in main-sequence envelopes and white dwarfs, due to composition gradients in neutron stars). We first illustrate it in a toy model involving a single, azimuthal magnetic flux tube. We then discuss the effect of stable stratification or its absence on more general configurations, such as axisymmetric equilibria involving poloidal and toroidal field components. We argue that the main mode of decay for these configurations are processes that lift the constraints set by stable stratification, such as heat diffusion in main-sequence envelopes and white dwarfs, and beta decays or particle diffusion in neutron stars. We estimate the time scales for these processes, as well as their interplay with the cooling processes in the case of neutron stars. Results. Stable magneto-hydrostatic equilibria appear to exist in stars whenever the matter in their interior is stably stratified (not barotropic). These equilibria are not force-free and not required to satisfy the Grad-Shafranov equation, but they do involve both toroidal and poloidal field components. In main sequence stars with radiative envelopes and in white dwarfs, heat diffusion is not fast enough to make these equilibria evolve over the stellar lifetime. In neutron stars, a strong enough field might decay by overcoming the compositional stratification through beta decays (at the highest field strengths) or through ambipolar diffusion (for somewhat weaker fields). These processes convert magnetic energy to thermal energy, and they occur at significant rates only once the latter is less than the former; therefore, they substantially delay the cooling of the neutron star, while slowly decreasing its magnetic energy.

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Section: Force Balancementioning

confidence: 99%

Section: Axially Symmetric Equilibriamentioning

confidence: 99%

Stable magnetic equilibria and their evolution in the upper main sequence, white dwarfs, and neutron stars

Reisenegger

2009

A&A

112

141

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“…the non-compact objects), the ratio of the volumetric Lorentz force by the gravity is very weak. Therefore, the stellar structure modifications induced by the field can be considered as perturbations only from a spherically symmetric background (Haskell et al 2008). Then, we can write ρ ≈ ρ + ρ, where ρ and ρ are, respectively, the mean density on an isobar, which is given at the first order by the standard non-magnetic radial density profile of the considered star, and its magnetic-induced perturbation on the isobar (with ρ< < ρ).…”

Section: The Barotropic Equilibrium State Familymentioning

confidence: 99%

“…Such an approach has already been applied to investigate the internal magnetic configurations in polytropes and in compact objects such as white dwarfs or neutron stars (see e.g. Monaghan 1976;Payne & Melatos 2004;Tomimura & Eriguchi 2005;Yoshida et al 2006;Haskell et al 2008;Akgün & Wasserman 2008;Kiuchi & Kotake 2008).…”

Section: Fossil Fields In Early-type Starsmentioning

confidence: 99%

Relaxed equilibrium configurations to model fossil fields

Duez

Mathis

2010

A&A

130

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Context. The understanding of fossil fields' origin, topology, and stability is one of the corner stones of the stellar magnetism theory. On one hand, since they survive on secular time scales, they may modify the structure and the evolution of their host stars. On the other hand, they must have a complex stable structure since it has been demonstrated that the simplest purely poloidal or toroidal fields are unstable on dynamical time scales. In this context, the only stable configuration found today is the one resulting from a numerical simulation by Braithwaite and collaborators who studied the evolution of an initial stochastic magnetic field, which is found to relax on a mixed stable configuration (poloidal and toroidal) that seems to be in equilibrium and then diffuses. Aims. We investigate an equilibrium field in a semi-analytical way. In this first article, we study the barotropic magnetohydrostatic equilibrium states. Methods. The problem reduces to a Grad-Shafranov-like equation with arbitrary functions. These functions are constrained by deriving the lowest-energy equilibrium states for given invariants of the considered axisymmetric problem, in particular for a given helicity known to be one of the causes of such problems. These theoretical results were applied to realistic stellar cases, the solar radiative core and the envelope of an Ap star, and discussed. In both cases we assumed that the field is initially confined in the stellar radiation zone.Results. The generalization of the force-free Taylor's relaxation states studied in laboratory experiments (in spheromaks) that become non force-free in the self-gravitating stellar case are obtained. The case of general baroclinic equilibrium states will be studied in Paper II.

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“…As a general rule of thumb, a neutron star's ellipticity scales with the square of the volume-averaged magnetic field inside the star, B (e.g., Haskell et al 2008), implying the characteristic gravitational wave strain also scales as h 0 ∼ B 2 . The dipole, poloidal component of the magnetic field at the surface of the star is inferred from the star's spin period and its derivative, but very little is known about the interior field strength and/or configuration.…”

Section: Magnetic Field-induced Ellipticitiesmentioning

confidence: 99%

Gravitational Waves from Neutron Stars: A Review

Lasky

2015

Publ. Astron. Soc. Aust.

168

109

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Neutron stars are excellent emitters of gravitational waves. Squeezing matter beyond nuclear densities invites exotic physical processes, many of which violently transfer large amounts of mass at relativistic velocities, disrupting spacetime and generating copious quantities of gravitational radiation. I review mechanisms for generating gravitational waves with neutron stars. This includes gravitational waves from radio and millisecond pulsars, magnetars, accreting systems, and newly born neutron stars, with mechanisms including magnetic and thermoelastic deformations, various stellar oscillation modes, and core superfluid turbulence. I also focus on what physics can be learnt from a gravitational wave detection, and where additional research is required to fully understand the dominant physical processes at play.

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Modelling magnetically deformed neutron stars

Cited by 210 publications

References 30 publications

Stable magnetic equilibria and their evolution in the upper main sequence, white dwarfs, and neutron stars

Stable magnetic equilibria and their evolution in the upper main sequence, white dwarfs, and neutron stars

Relaxed equilibrium configurations to model fossil fields

Gravitational Waves from Neutron Stars: A Review

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