Magnetic Field Reconnection Research Articles

“Cosmic alternator” for the onset of large-scale magnetic fields

Magnetic field configurations extending over macroscopic scale distances are shown to be generated in rarefied collisionless plasmas when non-thermal and spatially inhomogeneous electron distributions in phase space emerge. The analyzed representative case is where, in the presence of a significant spatial gradient of the electron pressure and of a sheared magnetic field configuration, an alternating magnetic field reconnection process can develop associated with the anisotropy of the fluctuating electron temperature. The relevant process is intrinsically different from that known as the “Biermann Battery,” which does not involve magnetic reconnection and requires that the unperturbed spatial gradient of the (isotropic) electron temperature be misaligned relative to that of the density gradient.

Probing the peripheral self-generated magnetic field distribution in laser-plasma magnetic reconnection with Martin–Puplett interferometer polarimeter

Magnetic reconnection of the self-generated magnetic fields in laser-plasma interaction is an important laboratory method for modeling high-energy density astronomical and astrophysical phenomena. We use the Martin–Puplett interferometer (MPI) polarimeter to probe the peripheral magnetic fields generated in the common magnetic reconnection configuration, two separated coplanar plane targets, in laser-target interaction. We introduce a new method that can obtain polarization information from the interference pattern instead of the sinusoidal function fitting of the intensity. A bidirectional magnetic field is observed from the side view, which is consistent with the magneto-hydro-dynamical (MHD) simulation results of self-generated magnetic field reconnection. We find that the cancellation of reverse magnetic fields after averaging and integration along the observing direction could reduce the magnetic field strength by one to two orders of magnitude. It indicates that imaging resolution can significantly affect the accuracy of measured magnetic field strength.

Analysis of the Energy Flux Density near Electron Diffusion Region of Asymmetric Magnetic Field Reconnection

Magnetic reconnection is a crucial energy conversion process in plasmas, and it is important to study the forms of energy conversion and their distribution in this process. Previous research has focused mainly on the energy fluxes in symmetric reconnection, while the study of asymmetric reconnection at the Earth’s magnetopause, especially in terms of statistical analysis of multiple events, has not been reported before. Therefore, 10 magnetic reconnection events at the magnetopause observed by MMS (Magnetospheric Multiscale) satellite that passed through the electron diffusion region were used for analysis. Although the contribution of different energy flux varies case by case, our results show that in most events, the ion enthalpy flux is dominant, followed by the Poynting flux. The ion heat flux is slightly smaller than the Poynting flux, while the sum of ion kinetic energy flux, electron enthalpy flux and electron heat flux only accounts for less than 10% of the total energy flux. By projecting the normalized energy flux of all events into BL−V(i,L) plane (in LMN coordinate), we find that the energy flux in M direction is comparable to the energy flux in L direction and also there is an “anti-correlated” relationship between the ion velocity and ion heat flux around reconnection diffusion region, consistent with previous studies.

Bridging Scales in Black Hole Accretion and Feedback: Magnetized Bondi Accretion in 3D GRMHD

Fueling and feedback couple supermassive black holes (SMBHs) to their host galaxies across many orders of magnitude in spatial and temporal scales, making this problem notoriously challenging to simulate. We use a multi-zone computational method based on the general relativistic magnetohydrodynamic (GRMHD) code KHARMA that allows us to span 7 orders of magnitude in spatial scale, to simulate accretion onto a non-spinning SMBH from an external medium with a Bondi radius of R B ≈ 2 × 105 GM •/c 2, where M • is the SMBH mass. For the classic idealized Bondi problem, spherical gas accretion without magnetic fields, our simulation results agree very well with the general relativistic analytic solution. Meanwhile, when the accreting gas is magnetized, the SMBH magnetosphere becomes saturated with a strong magnetic field. The density profile varies as ∼r −1 rather than r −3/2 and the accretion rate is consequently suppressed by over 2 orders of magnitude below the Bondi rate . We find continuous energy feedback from the accretion flow to the external medium at a level of . Energy transport across these widely disparate scales occurs via turbulent convection triggered by magnetic field reconnection near the SMBH. Thus, strong magnetic fields that accumulate on horizon scales transform the flow dynamics far from the SMBH and naturally explain observed extremely low accretion rates compared to the Bondi rate, as well as at least part of the energy feedback.

Transition acceleration of electrons and reconnection of magnetic fields driven by two-beam relativistic laser pulses traversing a NCD plasma slab target

The self-generation and reconnection of magnetic fields and accompanying electron acceleration were studied when two ultrafast intense laser beams propagate synchronously through a thin plasma slab target with homogeneous near-critical density (NCD). The results show that the magnetic reconnection occurs behind the target and the electrons undergo three important accelerating stages, ponderomotive force acceleration in the plasma channels, transition (or transboundary) acceleration from the plasma medium to the vacuum, and acceleration by the reconnecting fields. In the reconnection process the hot electrons are compelled to be reverse-accelerated (generating refluxes) and consequently the double annular magnetic tube fields in channels are collapsed into one large-scale annular magnetic tube structure, in which a significant pinching effect is revealed. Meanwhile, two peculiar enclosed “field-free” zones were shown, which is suggested to be a combined effect of magnetic annihilation (MA) and longitudinal quasi-static electric field generated by separation of positive and negative charges.

High-energy synchrotron flares powered by strongly radiative relativistic magnetic reconnection: 2D and 3D PIC simulations

ABSTRACT The time evolution of high-energy synchrotron radiation generated in a relativistic pair plasma energized by reconnection of strong magnetic fields is investigated with 2D and 3D particle-in-cell (PIC) simulations. The simulations in this 2D/3D comparison study are conducted with the radiative PIC code OSIRIS, which self-consistently accounts for the synchrotron radiation reaction on the emitting particles, and enables us to explore the effects of synchrotron cooling. Magnetic reconnection causes compression of the plasma and magnetic field deep inside magnetic islands (plasmoids), leading to an enhancement of the flaring emission, which may help explain some astrophysical gamma-ray flare observations. Although radiative cooling weakens the emission from plasmoid cores, it facilitates additional compression there, further amplifying the magnetic field B and plasma density n, and thus partially mitigating this effect. Novel simulation diagnostics utilizing 2D histograms in the n-B space are developed and used to visualize and quantify the effects of compression. The n-B histograms are observed to be bounded by relatively sharp power-law boundaries marking clear limits on compression. Theoretical explanations for some of these compression limits are developed, rooted in radiative resistivity or 3D kinking instabilities. Systematic parameter-space studies with respect to guide magnetic field, system size, and upstream magnetization are conducted and suggest that stronger compression, brighter high-energy radiation, and perhaps significant quantum electrodynamic effects such as pair production, may occur in environments with larger reconnection-region sizes and higher magnetization, particularly when magnetic field strengths approach the critical (Schwinger) field, as found in magnetar magnetospheres.

Magnetic field evolution and reconnection in low resistivity plasmas

The mathematics and physics of each of the three aspects of magnetic field evolution—topology, energy, and helicity—are remarkably simple and clear. When the resistivity η is small compared to an imposed evolution, a/v, timescale, which means Rm≡μ0va/η≫1, magnetic field-line chaos dominates the evolution of field-line topology in three-dimensional systems. Chaos has no direct role in the dissipation of energy. A large current density, jη≡vB/η, is required for energy dissipation to be on a comparable timescale to the topological evolution. Nevertheless, chaos plus Alfvén wave damping explain why both timescales tend to be approximately an order of magnitude longer than the evolution timescale a/v. Magnetic helicity is injected onto tubes of field lines when boundary flows have vorticity. Chaos can spread but not destroy magnetic helicity. Resistivity has a negligible effect on helicity accumulation when Rm≫1. Helicity accumulates within a tube of field lines until the tube erupts and moves far from its original location.

Dark photon superradiance: Electrodynamics and multimessenger signals

We study the electrodynamics of a kinetically mixed dark photon cloud that forms through superradiance around a spinning black hole, and design strategies to search for the resulting multimessenger signals. A dark photon superradiance cloud sources a rotating dark electromagnetic field which, through kinetic mixing, induces a rotating visible electromagnetic field. Standard model charged particles entering this field initiate a transient phase of particle production that populates a plasma inside the cloud and leads to a system which shares qualitative features with a pulsar magnetosphere. We study the electrodynamics of the dark photon cloud with resistive magnetohydrodynamics methods applicable to highly magnetized plasma, adapting techniques from simulations of pulsar magnetospheres. We identify turbulent magnetic field reconnection as the main source of dissipation and electromagnetic emission, and compute the peak luminosity from clouds around solar-mass black holes to be as large as $10^{43}$ erg/s for open dark photon parameter space. The emission is expected to have a significant X-ray component and is potentially periodic, with period set by the dark photon mass. The luminosity is comparable to the brightest X-ray sources in the Universe, allowing for searches at distances of up to hundreds of Mpc with existing telescopes. We discuss observational strategies, including targeted electromagnetic follow-ups of solar-mass black hole mergers and targeted continuous gravitational wave searches of anomalous pulsars.

Quasi-elastodynamic Processes Involved in the Interaction between Solar Wind and Magnetosphere

The interaction between the solar wind and the magnetosphere is one of the most important research subjects in the fields of astrophysics and space physics. For more than half a century, based on the pressure balance assumption between the solar wind and the magnetosphere and considering other important factors, such as the interplanetary magnetic field and magnetic reconnection process, the dynamic processes at the magnetopause have been extensively analyzed. However, the responses of magnetopause to the solar wind dynamic pressure variations are still complicated to understand. Here, we show that the interaction between the solar wind and the magnetosphere can be regarded as a quasi-elastodynamic process. The driving frequency of the solar wind is determined as a crucial reason for the phase difference between solar wind dynamic pressure variations and magnetopause standoff distance. The low-pass filter effect and oscillation properties of the magnetopause can also be well explained by the forced damped vibrations. Moreover, the quasi-elastodynamic processes predict deformations at the magnetopause, which resemble the magnetopause surface wave. Finally, a three-dimensional time-dependent magnetopause model is constructed and verified by observation. Based on 12,242 magnetopause crossing events, it is found that the new model reveals ∼9.7% better prediction accuracy than the widely used time-independent model. These results can also shed light on our understanding of the solar-wind–magnetopause interaction for other planets.

Magnetic Reconnection as the Driver of the Solar Wind

We present EUV solar observations showing evidence for omnipresent jetting activity driven by small-scale magnetic reconnection at the base of the solar corona. We argue that the physical mechanism that heats and drives the solar wind at its source is ubiquitous magnetic reconnection in the form of small-scale jetting activity (a.k.a. jetlets). This jetting activity, like the solar wind and the heating of the coronal plasma, is ubiquitous regardless of the solar cycle phase. Each event arises from small-scale reconnection of opposite-polarity magnetic fields producing a short-lived jet of hot plasma and Alfvén waves into the corona. The discrete nature of these jetlet events leads to intermittent outflows from the corona, which homogenize as they propagate away from the Sun and form the solar wind. This discovery establishes the importance of small-scale magnetic reconnection in solar and stellar atmospheres in understanding ubiquitous phenomena such as coronal heating and solar wind acceleration. Based on previous analyses linking the switchbacks to the magnetic network, we also argue that these new observations might provide the link between the magnetic activity at the base of the corona and the switchback solar wind phenomenon. These new observations need to be put in the bigger picture of the role of magnetic reconnection and the diverse form of jetting in the solar atmosphere.

Analysis of the Energy Flux Density near Electron Diffusion Region of Asymmetric Magnetic Field Reconnection

Analysis of the Energy Flux Density near Electron Diffusion Region of Asymmetric Magnetic Field Reconnection

Evolution of magnetic fields in cosmic string wakes

We study the evolution of magnetic fields in cosmic string wakes in a plasma with a low resistivity. The initial magnetic field in the wake is modelled on the magnetic fields that are generated by the motion of particles around cosmic strings. The plasma is characterized by a high beta value. We find multiple shock like structures developing in the wake of the string. We study the detailed structure of the shocks formed and the evolution of the magnetic field in the shock using a 2-D magnetohydrodynamic simulation. As expected, the development of the magnetic field does not depend on the β value. Our results show that instead of a single uniform shock forming behind the cosmic string we have multiple shocks forming at short time intervals behind the string. The presence of multiple shocks will definitely affect the observational signatures of cosmic string wakes as these signatures depend upon the temperature fluctuations generated by the shock. We also find that as the shock moves away, the residual magnetic field left behind reconnects and dissipates rapidly. The magnetic field around the string is thus very localized. We find that magnetic field reconnections take place in cosmic string wakes. This leads to the decrease of the magnetic field in the post shock region.

Detection of current-sheet and bipolar ion flows in a self-generated antiparallel magnetic field of laser-produced plasmas for magnetic reconnection research.

Magnetic reconnection in laser-produced magnetized plasma is investigated by using optical diagnostics. The magnetic field is generated via the Biermann battery effect, and the inversely directed magnetic field lines interact with each other. It is shown by self-emission measurement that two colliding plasmas stagnate on a midplane, forming two planar dense regions, and that they interact later in time. Laser Thomson scattering spectra are distorted in the direction of the self-generated magnetic field, indicating asymmetric ion velocity distribution and plasma acceleration. In addition, the spectra perpendicular to the magnetic field show different peak intensity, suggesting an electron current formation. These results are interpreted as magnetic field dissipation, reconnection, and outflow acceleration. Two-directional laser Thomson scattering is, as discussed here, a powerful tool for the investigation of microphysics in the reconnection region.

Scaling of reconnection parameters in magnetic island coalescence: Role of in-plane shear flow

A 2D incompressible viscoresistive-MHD model [Mahapatra et al., Phys. Plasmas 28, 072103 (2021)] is used to study the scaling of reconnection parameters in the magnetic island coalescence problem under two interesting scenarios. First, the effect of changing island half-width at a fixed system size is investigated. As the island half-width increases, the total magnetic flux content of the islands increases, resulting in an increase in upstream magnetic field, upstream velocity field, and unnormalized reconnection rate. However, the downstream magnetic field, current sheet length and normalized reconnection rate (normalized to the upstream magnetic field and upstream Alfvénic velocity) remain independent of it. Interestingly, the reconnection rate is found to be different from the upstream to downstream velocity ratio as well as from the aspect ratio of the current sheet, as opposed to the findings of the Sweet–Parker model. Second, the in-plane shear flow effects are studied, keeping the island width and system size fixed. Here, thickness and length of the current sheet, the upstream magnetic and velocity field components, reconnection rate and time, current sheet inclination angle with shear flow length scale, and amplitude are calculated. Interestingly, the inclination angle of the current sheet and the diffusion region are found to be different, and the differences are more in stronger shear flows. These results are significantly different from the Harris sheet setup with shear flow.

A magnetohydrodynamic simulation of the dayside magnetic reconnection between the solar wind and the Martian crustal field

Using a three-dimensional multispecies magnetohydrodynamic model, we study the effects of the orientation of the interplanetary magnetic field (IMF), solar wind dynamic pressure (Pd), and the location of the intense crustal field, on the dayside magnetic reconnection between the solar wind and the Martian crustal field. Our main results are as follows: (1) Different IMF orientations result in different magnetic field configurations and reconnection conditions on the Martian dayside. When the intense crustal field is located on the dayside, the dayside magnetic reconnection tends to occur in the region with solar zenith angles (SZA) ≈45° in the southern hemisphere for the IMF with a southward component. When the IMF has a northward component, the magnetic field lines are piled up in the same place and the Martian magnetic pileup boundary (MPB) appears as a local bulged “mini-magnetopause”. Under the pure radial IMF, the magnetic reconnection is absent, which might be due to the presence of additional outward magnetic tension and kinetic effects. (2) Dayside reconnection can change the shape of the Martian MPB, while the bow shock is weakly affected. When the IMF has a southward component, the dayside magnetic reconnection happens and the MPB is located closer to Mars with a “cusp” shape. When the IMF has a northward component, the Martian MPB expands with a local bulged “mini-magnetopause”. For the pure radial IMF condition, the subsolar region of the MPB is located closer to Mars than that under other IMF directions. The influence of the IMF cone angles on the Martian bow shock is much less than that on the MPB, and the bow shock locations are very close to the model results of another author found in the literature. (3) With increasing Pd, the size of the crustal field region decreases and the draped fields correspondingly move to lower altitudes where the IMF and crustal field have the same direction. When the IMF has a southward component and the magnetic reconnection occurs at SZA ≈ 45°, the reconnection site, the region of the closed topology of the crustal field, and the draped IMF, do not change much with increasing Pd. We suggest that the multipolar crustal magnetic fields can protect the solar wind IMF from further reconnecting with the crustal field to a lower altitude when Pd is enhanced.

Radial and Local Time Variations in the Thickness of Jupiter's Magnetospheric Current Sheet

AbstractThe magnetic field observations from the Galileo, Ulysses, Voyager 1 and 2, and Pioneer 10 and 11 spacecraft are analyzed to understand the structures and thickness of the Jovian magnetospheric current sheet. Using a new technique that can determine the motion of the spacecraft relative to the current sheet, we have built the first global map of the thickness of the Jovian magnetospheric current sheet. We show that the current sheet thickness in Jupiter's magnetosphere is not equal everywhere but changes systematically with both radial distance and local time. The extremely thin dawnside current sheet appears to be linked to the stresses imposed by the solar wind on the open magnetic flux housed in the lobes of the magnetosphere in that sector. We also show evidence of a mostly closed magnetosphere in the dusk sector. We show that the current sheet thickness asymmetries likely arise from a field and plasma convection system set up by the reconnection of the interplanetary magnetic field with that of Jupiter.

A Double-decker Filament Formation Driven by Sunspot Rotation and Magnetic Reconnection

In this paper, through analyzing data from the Solar Dynamics Observatory (SDO) and the Global Oscillation Network Group (GONG), we present a study on the formation of a double-decker filament in NOAA Active Region 12665 from 2017 July 8 to 14. We find that magnetic reconnection occurs between two smaller filaments to form a longer filament. According to the evolution of the leading sunspot, it is obvious that the sunspot experiences a continuous rotation around its umbra. During the period from 03:00 UT on July 11 to 10:00 UT on July 14, the average speed of sunspot rotation is about 3.°7 hr–1. The continuous rotation of sunspot stretches the filament and results in the formation of a reversed S-shaped filament. Due to the motion of the magnetic field and internal magnetic reconnection, the filament splits into two branches and forms a double-decker filament structure. In the process of filament separation, internal magnetic reconnection can also accelerate the filament separation. Nonlinear force-free field extrapolation indicates that there are two magnetic flux ropes, which are consistent with the observed results. Eventually, the upper filament erupts and produces an M-class flare and a halo coronal mass ejection.

Short-term variability of DS Tucanae A observed with TESS

Context. Impulsive short-term variations occur in all kinds of solar-type stars and are the result of complex phenomena such as stellar magnetic field reconnection, low-level variability, or in some cases even star-planet interactions. The radiation arising from these events is often highly energetic and, in stars hosting planets, may interact with the planetary atmospheres. Studying the rate of these energetic phenomena is fundamental to understanding their role in modifying the chemical composition or, in some extreme cases, the disruption of the planetary atmospheres. Aims. Here, we present a new procedure developed to identify the impulsive events in Transit Exoplanet Survey Satellite (TESS) light curves. Our goal is to produce a simple and effective tool with which to study the short-term activity of a star using only its light curve in order to derive the distribution and energy of short-term variations. As our first case, we studied the system DS Tuc. Methods. Our technique consists of fitting the TESS light curves using iteratively Gaussian processes in order to remove all the longterm stellar activity contributions. We then identify the impulsive events and derive amplitudes, timescales, and the amount of energy emitted. Results. We validate our procedure using the AU Mic TESS light curves, obtaining results consistent with those presented in the literature. We estimate the frequency distribution of energetic events for DS Tuc. In particular, we find that there are approximately two events per day with energy greater than 2 × 1032 erg. We find evidence for a favoured stellar phase for short-term activity on AU Mic, and also indications of short-term activity in phase with the planetary orbit. For DS Tuc, we find that the event distribution is not equally spaced in time but often grouped. The resulting distribution may be used to estimate the impact of short-term variability on planetary atmosphere chemical compositions.

High-energy neutrinos from fast winds in novae

ABSTRACT We discuss a scenario in which TeV neutrinos are produced during explosions of novae. It is argued that hadrons are accelerated to very high energies in the inner part of a nova wind, as a result of reconnection of the strong magnetic field of a white dwarf. Hadrons are expected to interact efficiently with a dense matter of the wind, either already during the acceleration process or during their advection with the equatorial wind. We calculate the neutrino spectra and estimate the muon neutrino event rates in the IceCube telescope, in the case of a few novae. In general, those event rates are unlikely to be detected with the present neutrino detectors. However, for a favourable location of the observer, some neutrino events might be detected not only from the class of novae recently detected in the GeV γ-rays by the Fermi-LAT (Large Area Telescope), but also from novae not detected in γ-rays. The GeV γ-ray emission observed from novae cannot originate in terms of the model discussed here, since protons are accelerated within a few stellar radii of the white dwarf, i.e. in the region in which GeV γ-rays are expected to be severely absorbed in the interactions with the radiation field and the matter of the wind.

Effect of Magnetic Field Dissipation on Primordial Li Abundance

Abstract The dissipation effects of primordial magnetic fields on the primordial elemental abundances were investigated. When a magnetic field reconnects, its energy is converted to the kinetic energy of charged particles, as observed for solar energetic particles arriving on Earth. This accelerates the cosmic background nuclei and energetic nuclei induce nonthermal reactions. A constraint on the dissipation is derived from a theoretical calculation of the nonthermal reactions during Big Bang nucleosynthesis. We found that observations of the Li and D abundances can be explained if 0.01%–0.1% of the cosmic energy density was utilized for nuclear acceleration after the electron–positron annihilation epoch. Reconnections of such amplitudes of magnetic fields generate outgoing jets, the bulk velocity of which evolves to values appropriate for cosmic-ray (CR) nuclear energies of 0.1–1 MeV necessary for successful CR nucleosynthesis. Therefore, acceleration of cosmic background nuclei during the dissipation of primordial magnetic fields is a possible generation mechanism of soft CRs that has been suggested as a solution to the cosmic Li problem. Among the solutions suggested without exotic physics, only the dissipating magnetic field model suggested here explains observations of both low Li and high D abundances. Our results demonstrate that signatures of strong magnetic fields in the early universe have been observed in primordial elemental abundances.