We study magnetohydrodynamic stability of neutron star core matter composed of neutrons, protons and leptons threaded by a magnetar-strength magnetic field $10^{14}$--$10^{17}$ G, where quantum electrodynamical effects and Landau quantization of fermions are important. Stability is determined using the Friedman--Schutz formalism for the canonical energy of fluid perturbations, which we calculate for a magnetizable fluid with $H\neq B$. Using this and the Euler--Heisenberg--Fermi--Dirac Lagrangian for a strongly magnetized fluid of Landau-quantized charged fermions, we calculate the local stability criteria for a fluid slab as a stand-in for a segment of a neutron star core, accounting for magnetic and composition gradient buoyancy. The slab is threaded by a field orthogonal to the gravitational field, the Cartesian analogy to a toroidal field. We find that, for sufficiently strong fields $B\gtrsim10^{15}$ G, the magnetized fluid is unstable to a magnetosonic-type instability with growth times of order $10^{-3}$ s. The instability is triggered by sharp changes in the second-order field derivative of the Euler--Heisenberg--Fermi--Dirac Lagrangian which occur where additional Landau levels start being populated. These sharp changes are divergent at zero temperature, but are finite for nonzero temperature, so realistic neutron star core temperatures $5\times10^7$ K$<T<5\times10^8$ K are used. We conjecture that this mechanism could promote the formation of magnetic domains as predicted by Blandford and Hernquist (1982) and Suh and Mathews (2010).
We study the stability of Hall MHD with strong magnetic fields in which Landau quantization of electrons is important. We find that the strong-field Hall modes can be destabilized by the dependence of the differential magnetic susceptibility on magnetic field strength. This instability is studied using linear perturbation theory, and is found to have typical growth time of order $\lesssim 10^3$ yrs, with the growth time decreasing as a function of wavelength of the perturbation. The instability is self-limiting, turning off following a period of local field growth by a few percent of the initi…
Relativistic Magnetohydrodynamic Simulations of Giant Magnetar Bursts
University of Maryland（马里兰大学）；Institute for Research in Electronics and Applied Physics, University of Maryland（马里兰大学电子与应用物理研究所）；Canadian Institute for Theoretical Astrophysics（加拿大理论天体物理研究所）；Columbia University（哥伦比亚大学）；Physics Department and Columbia Astrophysics Laboratory, Columbia University（哥伦比亚大学物理系与哥伦比亚天体物理实验室）；Max Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；Princeton Plasma Physics Laboratory（普林斯顿等离子体物理实验室）；University of Toronto（多伦多大学）；David A. Dunlap Department of Astronomy, University of Toronto（多伦多大学大卫·A·邓普尔天文学系）；Perimeter Institute for Theoretical Physics（基础物理研究所）；TAPIR, Mailcode 350-17, California Institute of Technology（加州理工学院 TAPIR (Mailcode 350-17)）
Observations of powerful radio waves from neutron star magnetospheres raise the question of how strong waves interact with particles in a strong background magnetic field $B_{bg}$. This problem is examined by solving the particle motion in the wave. Remarkably, waves with amplitudes $E_0>B_{bg}$ pump particle energy via repeating resonance events, quickly reaching the radiation reaction limit. As a result, the wave is scattered with a huge cross section. This fact has implications for models of fast radio bursts and magnetars. Particles accelerated in the wave emit gamma-rays, which can trigge…
Possessing the strongest magnetic fields in the Universe, magnetars mark an extremum of physical phenomena. The strength of their magnetic fields is sufficient to deform the shape of the stellar body, and when the rotational and magnetic axes are not aligned, these deformations lead to the production of gravitational waves (GWs) via a time-varying quadrupole moment. Such gravitational radiation differs from signals presently detectable by the Laser Interferometer Gravitational-Wave Observatory. These signals are continuous rather than the momentary 'chirp' waveforms produced by binary systems …
We perform the first magnetohydrodynamic simulations in full general relativity of self-consistent rotating neutron stars (NSs) with ultrastrong mixed poloidal and toroidal magnetic fields. The initial uniformly rotating NS models are computed assuming perfect conductivity, stationarity, and axisymmetry. Although the specific geometry of the mixed field configuration can delay or accelerate the development of various instabilities known from analytic perturbative studies, all our models finally succumb to them. Differential rotation is developed spontaneously in the cores of our magnetars whic…
This paper continues the approach of Kostenko \& Thompson to calculating quantum electrodynamic processes in the ultrastrong magnetic field near some neutron stars, such as magnetars or merging binary neutron stars. Here we consider electron-positron scattering, the Coulomb scattering of electrons and positrons off ions, and relativistic $e^\pm$-ion bremsstrahlung. The evaluation of differential and total cross sections simplifies considerably when the magnetic field lies in the range $10^3B_{\rm Q} \gg B \gg B_{\rm Q}$, where $B_{\rm Q} \equiv m^2/e = 4.4\times 10^{13}$ G. Then, relativistic …
We evaluate several basic electrodynamic processes as modified by the presence of a very strong magnetic field, exceeding $B_{\rm Q} \equiv m^2/e = 4.4\times 10^{13}$ G. These results are needed to build models of dissipative phenomena outside magnetars and some other neutron stars. Differential and total cross sections and rates are presented for electron-photon scattering, the annihilation of an electron-positron pair into two photons, the inverse process of two-photon pair creation, and single-photon pair creation into the lowest Landau state. The relative importance of these interactions c…
Anomalous X-ray pulsars and soft gamma repeaters are slowly rotating, young, and isolated neutron stars exhibiting sporadic outbursts and high X-ray quiescent luminosities. They are believed to be powered by ultrastrong magnetic fields, $B\sim10^{14}-10^{15}$ G, associated with `magnetars'. In the peculiar case of SGR 0418+5729, timing parameters imply a dipolar $B$-field of $6.1\times10^{12}$ G. This discovery has challenged the traditional picture of magnetars in terms of $B$-field strengths, evolutionary stages, and ages. Here we provide a novel approach to estimate a magnetar's age by cons…
The photon spectrum emitted by a transrelativistic pair plasma is calculated in the presence of an ultrastrong magnetic field, and is shown to bear a remarkable resemblance to the rising hard X-ray spectra of quiescent magnetars. This emission is powered by pair annihilation which, in contrast with a weakly magnetized pair plasma, shows an extended low-frequency tail similar to bremsstrahlung. Cross sections for electron-positron annihilation/scattering, two-photon pair creation, and photon-$e^\pm$ scattering are adopted from our earlier ab initio QED calculations in the regime $10α_{\rm em}^{…
Magnetar magnetothermal evolution with Landau-quantized electrons: enhanced Joule heating due to free electron diamagnetism and the magnetar heating problem
Columbia Astrophysics Laboratory, Columbia University（哥伦比亚大学天体物理实验室，哥伦比亚大学）
Magnetohydrodynamic (MHD) turbulence is of key importance in many high-energy astrophysical systems, where MHD instabilities can amplify local magnetic field over very short time scales. Specifically, the magnetorotational instability (MRI) and dynamo action have been suggested as a mechanism to grow magnetar-strength magnetic field ($\ge10^{15} G$) and magnetorotationally power the explosion of a rotating massive star. Such stars are progenitor candidates for type Ic-bl hypernova explosions and make up all supernovae connected to long gamma-ray bursts (GRBs). The MRI has been studied with loc…
Magnetar flares excite strong Alfvén waves in the magnetosphere of the neutron star. The wave energy can (1) dissipate in the magnetosphere, (2) convert to "fast modes" and possibly escape, and (3) penetrate the neutron star crust and dissipate there. We examine and compare the three options. Particularly challenging are nonlinear interactions between strong waves, which develop a cascade to small dissipative scales. This process can be studied in the framework of force-free electrodynamics (FFE). We perform three-dimensional FFE simulations to investigate Alfvén wave dissipation, how long it …
Interior Magnetic Fields in Magnetars and Radio Pulsars
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）；Department of Physics, University of Milan（米兰大学物理系）；INFN, Sezione di Milano（意大利国家核物理研究所米兰分部）；Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universität Jena（耶拿弗里德里希·席勒大学理论物理研究所）
Axion magnetohydrodynamics and reconnection-driven axion bursts
Instituto Superior de Engenharia de Lisboa, Instituto Politécnico de Lisboa（里斯本高等工程学院，里斯本理工学院）；GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa（等离子体与核聚变研究所，里斯本技术学院，里斯本大学）
We develop a model for the radio afterglow of the giant flare of SGR 1806-20 arising due to the interaction of magnetically-dominated cloud, an analogue of Solar Coronal Mass Ejections (CMEs), with the interstellar medium (ISM). The CME is modeled as a spheromak-like configuration. The CME is first advected with the magnetar's wind and later interacts with the ISM, creating a strong forward shock and complicated backwards exhaust flow. Using three-dimensional magnetohydrodynamic simulations, we study various relative configurations of the magnetic field of the CME with respect to the ISM's mag…
Magnetars are neutron stars presenting bursts and outbursts of X- and soft-gamma rays that can be understood with the presence of very large magnetic fields. Thus, nonlinear electrodynamics should be taken into account for a more accurate description of such compact systems. We study that in the context of ideal magnetohydrodynamics and make a realization of our analysis to the case of the well-known Born-Infeld (BI) electromagnetism in order to come up with some of its astrophysical consequences. We focus here on toroidal magnetic fields as motivated by already known magnetars with low dipola…
A Magnetar Strength Surface Magnetic Field for the Slowly Spinning Down SGR 0418+5729
观测到的典型软伽马射线中继站SGR 0418+5729的自旋下降速率上限对将该源解释为具有超强磁场的中子星提出了挑战。电流限值意味着偶极磁场强度小于7.5 x 10^{12} G（Rea等人，2010年），明显小于典型SGR。中子星的X射线光谱不依赖于从X射线计时推断出的性质，而允许测量它们的磁场强度，因为它们在辐射平衡大气中由于存在磁场而从纯黑体中失真。在本文中，我们模拟SGR 0418+5729的高信噪比XMM牛顿谱，以限制中子星表面的磁场强度。我们的分析表明，具有中等磁场强度（10^{12-13} G）的中子星大气模型不能拟合X射线谱，而具有较强磁场的模型能够解释观测结果。我们发现表面的磁场强度为1.0 x 10^{14} G。这个值虽然低于迄今为止分析的所有其他SGR，但仍然足够高，可以从源产生观测到的X射线爆发。关于自旋下降极限，它还意味着磁场的显著非偶极结构。我们讨论了我们的光谱建模的结果，并与其他SGRs进行比较。
We analyze the magnetic field evolution in dense quark matter with unbroken chiral symmetry, which can be found inside quark and hybrid stars. The magnetic field evolves owing to the chiral magnetic effect in the presence of the electroweak interaction between quarks. In our study, we also take into account the magnetohydrodynamic turbulence effects in dense quark matter. We derive the kinetic equations for the spectra of the magnetic helicity density and the magnetic energy density as well as for the chiral imbalances. On the basis of the numerical solution of these equations, we find that tu…
A magnetar formation in binary neutron star merger
Max Planck Institute for Gravitational Physics (Albert Einstein Institute)（马克斯·普朗克引力物理研究所（阿尔伯特·爱因斯坦研究所））；Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所）；Department of Physics, Toho University（东海大学物理学系）
We investigate the influence of magnetic fields on the evolution of binary neutron-star (BNS) merger remnants via three-dimensional (3D) dynamical-spacetime general-relativistic (GR) magnetohydrodynamic (MHD) simulations. We evolve a postmerger remnant with an initial poloidal magnetic field, resolve the magnetoturbulence driven by shear flows, and include a microphysical finite-temperature equation of state (EOS). A neutrino leakage scheme that captures the overall energetics and lepton number exchange is also included. We find that turbulence induced by the magnetorotational instability (MRI…
On Chern-Simons corrections to magnetohydrodynamics equations
研究了（3+1）维Chern-Simons电动力学对磁化等离子体和场动力学方程的影响。在这个模型中，Chern-Simons（CS）部分由一个动力学赝标量场组成，它的时空导数与电磁场耦合。本文研究了非零电阻率等离子体中磁场演化方程的CS修正。在此背景下，我们重新考林定理，并观察到CS校正导致可能很小，但非零源项轴对称磁场。电场和磁场的标量积是赝标量场的源，因此，类星体和磁星可能是产生传播赝标量波的天体物理候选者。虽然在磁层的大部分区域中，对齐的电场会被流动的电荷短路，但在磁层附近存在真空间隙，预计会存在强$\vec E. \vec B$。本文导出了与脉冲星有关的时变$\vec E. \vec B$产生的赝标量场的波动解。
Relativistic jets from millisecond proto-magnetars
University of Greifswald（格赖夫斯瓦尔德大学）；Perimeter Institute for Theoretical Physics（基础物理研究所）；University of Guelph（圭尔夫大学）；Columbia University（哥伦比亚大学）；Flatiron Institute（平顿研究所）
Global Magnetohydrodynamic Simulations of Monster Shocks in Neutron Star Magnetospheres
University of Toronto（多伦多大学）；Canadian Institute for Theoretical Astrophysics（加拿大理论天体物理研究所）；D. A. Dunlap Department of Astronomy, University of Toronto（多伦多大学D.A.邓普尔天文学系）；Perimeter Institute for Theoretical Physics（理论物理前沿研究所）；Columbia University（哥伦比亚大学）；Max Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；California Institute of Technology（加州理工学院）；Walter Burke Institute for Theoretical Physics（沃尔特·伯克理论物理研究所）
Magnetothermal evolution of neutron star cores in the `weak-coupling' regime: implications of ambipolar diffusion for the quiescent X-ray luminosity of magnetars
Magnetar Formation from Accretion Induced Collapse of White Dwarfs
Friedrich-Schiller-Universität Jena（耶拿弗里德里希·席勒大学）；University of California, Berkeley（加州大学伯克利分校）；The Pennsylvania State University（宾夕法尼亚州立大学）；University of New Hampshire（新罕布什尔大学）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）
Neutron stars, and magnetars in particular, are known to host the strongest magnetic fields in the Universe. The origin of these strong fields is a matter of controversy. In this preliminary work, via numerical simulations, we study, for the first time in non-ideal general relativistic magnetohydrodynamic (GRMHD) regime, the growth of the magnetic field due to the action of the mean-field dynamo due to sub-scale, unresolved turbulence. The dynamo process, combined with the differential rotation of the (proto-)star, is able to produce an exponential growth of any initial magnetic seed field up …
The exponential amplification of initial seed magnetic fields in relativistic plasmas is a very important topic in astrophysics, from the conditions in the early Universe to the interior of neutron stars. While dynamo action in a turbulent plasma is often invoked, in the last years a novel mechanism of quantum origin has gained increasingly more attention, namely the Chiral Magnetic Effect (CME). This has been recognized in semi-metals and it is most likely at work in the quark-gluon plasma formed in heavy-ion collision experiments, where the highest magnetic fields in nature, up to B~10^18 G,…
Recent X-ray observations in the central compact remnant of Puppis A and other young pulsars have provided convincing evidence about the anti-magnetar nature of the so-called central compact objects (CCOs). The measured period derivative, corrected by the proper movement, provides exceptionally low superficial magnetic fields for such sources. Using the dipole radiation canonical model, the superficial magnetic field of the CCO (RX J0822-4300) in Puppis A was estimated to be $B\simeq 2.9 \times 10^{10}$ G. In this paper, we present a numerical model to interpret the unusual magnetic-field beha…
The presence of neutron stars in at least three ultraluminous X-ray sources is now firmly established and offers an unambiguous view of super-critical accretion. All three systems show long-timescale periods (60-80 days) in the X-rays and/or optical, two of which are known to be super-orbital in nature. Should the flow be classically super critical, i.e. the Eddington limit is reached locally in the disc (implying surface dipole fields that are sub-magnetar in strength), then the large scale-height flow can precess through the Lense-Thirring effect which could provide an explanation for the ob…
The impact of the magnetic field on postbounce supernova dynamics of non-rotating stellar cores is studied by performing three-dimensional magnetohydrodynamics simulations with spectral neutrino transport. The explodability of strongly and weakly magnetized models of $20$ and $27$ $M_{\odot}$ pre-supernova progenitors are compared. We find that although the efficiency for the conversion of the neutrino heating into turbulent energy including magnetic fields in the gain region is not significantly different between the strong and weak field models, the amplified magnetic field due to the neutri…
About 10% of stars more massive than ${\approx}\,1.5\,\mathrm{M}_\odot$ have strong, large-scale surface magnetic fields and are being discussed as progenitors of highly-magnetic white dwarfs and magnetars. The origin of these fields remains uncertain. Recent 3D magnetohydrodynamical simulations have shown that strong magnetic fields can be generated in the merger of two massive stars. Here, we follow the long-term evolution of such a 3D merger product in a 1D stellar evolution code. During a thermal relaxation phase after the coalescence, the merger product reaches critical surface rotation, …
