Helical Magnetic Field Research Articles

Filamentary Hierarchies and Superbubbles: Galactic Multiscale Magnetohydrodynamic Simulations of Giant Molecular Cloud to Star Cluster Formation

There is now abundant observational evidence that star formation is a highly dynamical process that connects filament hierarchies and supernova feedback from galaxy-scale kiloparsec filaments and superbubbles to giant molecular clouds (GMCs) on 100 pc scales and star clusters (1 pc). Here we present galactic multiscale MHD simulations that track the formation of structure from galactic down to subparsec scales in a magnetized, Milky Way–like galaxy undergoing supernova-driven feedback processes. We do this by adopting a novel zoom-in technique that follows the evolution of typical 3 kpc subregions without cutting out the surrounding galactic environment, allowing us to reach 0.28 pc resolution in the individual zoom-in regions. We find a wide range of morphologies and hierarchical structures, including superbubbles, turbulence, and kiloparsec atomic gas filaments hosting multiple GMC condensations that are often associated with superbubble compression, down to smaller-scale filamentary GMCs and star cluster regions within them. Gas accretion and compression ultimately drive filaments over a critical, scale-dependent line mass leading to gravitational instabilities that produce GMCs and clusters. In quieter regions, galactic shear can produce filamentary GMCs within flattened, rotating disklike structures on 100 pc scales. Strikingly, our simulations demonstrate the formation of helical magnetic fields associated with the formation of these disklike structures.

In-depth experimental search for a coupling between gravity and electromagnetism with steady fields

Any means to control gravity like electromagnetism is currently out of reach by many orders of magnitude even under extreme laboratory conditions. Some often poorly executed experiments or pseudoscience theories appear from time to time claiming for example anomalous forces from capacitors that suggest a connection between the two fields. We developed novel and high resolution horizontal-, vertical- and rotation-balances that allow to test electric devices completely shielded and remotely controlled under high vacuum conditions to perform the first in-depth search for such a coupling using steady fields. Our testing included a variety of capacitors of different shapes and compositions as well as for the first-time solenoids and tunneling currents from Zener diodes and varistors. A comprehensive coupling-scheme table was used to test almost all combinations including capacitors and solenoids with permittivity and permeability gradients as well as capacitors and varistors within crossed magnetic fields. We also tested a crossed-coil producing helical magnetic field lines as well as interactions between a pair of shielded toroidal coils to look for proposed extensions to Maxwell’s equations. No anomalous forces or torques down to the nano-Newton or nano-Newton-Meter range were found providing new limits many orders of magnitude below previous assessments ruling out claims or theories and providing a basis for future research on the topic.

Helicity of magnetic fields associated with non-relativistic electron vortex beams

The helicities of the magnetic fields associated with non-relativistic electron vortex beams are considered for radially extended Bessel modes. Investigating the helicity density of this system lies in realizing the unique electric and magnetic properties of electron vortex beams that influence their interactions with matter. We have evaluated the vector potential components needed for the derivation of the magnetic helicity density and found that this has a non-zero distribution. This is attributed entirely to the cylindrically symmetric density flux of the electron beam, which scales with the winding number ℓ . It is also related to the magnetic moments of the electron oriented along the z-direction, giving rise to the z-component of the magnetic field. We obtain different helicity distributions for different signs of winding number ±ℓ , which confirms the chiral character of the magnetic fields associated with the electron vortex beam. The physical consequences of taking the spin current density into consideration are also examined. This allows a comparison to be made between the evaluated total current helicities, one with and one without including the spin-polarization.

Axion magnetic resonance: A novel enhancement in axion-photon conversion

We identify a new resonance, axion magnetic resonance, that can greatly enhance the conversion rate between axions and photons. A series of axion search experiments rely on converting them into photons inside a constant magnetic field background. A common bottleneck of such experiments is the conversion amplitude being suppressed by the axion mass when ma≳10−4 eV. We point out that a spatial or temporal variation in the magnetic field can cancel the difference between the photon dispersion relation and that of the axion, hence greatly enhancing the conversion probability. We demonstrate that the enhancement can be achieved by both a helical magnetic field profile and a harmonic oscillation of the magnitude. Our approach can extend the projected ALPS II reach in the axion-photon coupling (gaγ) by two orders of magnitude at ma=10−3 eV with moderate assumptions (see .) Published by the American Physical Society 2024

Multiwavelength Polarization Observations of Mrk 501

Mrk 501 is a prototypical high-synchrotron-peaked blazar and serves as one of the primary targets for the Imaging X-ray Polarimetry Explorer (IXPE). In this study, we report X-ray polarization measurements of Mrk 501 based on six IXPE observations. The detection of X-ray polarization at a confidence level exceeding 99% is achieved in four out of the six observations conducted across the entire energy range (2–8 keV) of IXPE. The maximum polarization degree (ΠX) is measured to be 15.8% ± 2.8%, accompanied by a polarization angle (ψ X) of 98.°0 ± 5.°1 at a confidence level of 5.6σ. During the remaining two observations, only an upper limit of ΠX < 12% could be derived at the 99% confidence level. No temporal variability in polarization is observed throughout all six IXPE observations for Mrk 501. A discernible trend of energy-dependent variation in the polarization degree is detected in optical spectropolarimetry; however, no analogous indication is observed in ΠX. The chromatic behavior of Π and the consistent values of ψ across different frequencies from X-ray to radio bands, along with the agreement between ψ and jet position angle, strongly support the interpretation of the energy-stratified model with shock-accelerated particles in the jet of Mrk 501. Additionally, the possibility of the presence of a global helical magnetic field in the jet of Mrk 501 is discussed.

Magnetogenesis with gravitational waves and primordial black hole dark matter

Strongly supercooled first-order phase transitions (FOPTs) can produce primordial black hole (PBH) dark matter (DM) along with observable gravitational waves (GWs) from bubble collisions. Such FOPTs may also produce coherent magnetic fields generated by bubble collisions and by turbulence in the primordial plasma. Here we find that the requirement for PBH DM can produce large primordial magnetic fields which subsequently yield intergalactic magnetic fields in the present Universe (with magnitude ≲20 pG across coherence length scales of ≃0.001–0.01 Mpc, assuming maximally helical magnetic fields) that easily exceed lower bounds from blazar observations. We follow a largely model-independent approach and highlight the possibility of producing DM and observable multimessenger magnetic fields and GW signals visible in next generation experiments. Published by the American Physical Society 2024

Investigating the Properties of the Relativistic Jet and Hot Corona in AGN with X-ray Polarimetry

X-ray polarimetry has been suggested as a prominent tool for investigating the geometrical and physical properties of the emissions from active galactic nuclei (AGN). The successful launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 9 December 2021 has expanded the previously restricted scope of polarimetry into the X-ray domain, enabling X-ray polarimetric studies of AGN. Over a span of two years, IXPE has observed various AGN populations, including blazars and radio-quiet AGN. In this paper, we summarize the remarkable discoveries achieved thanks to the opening of the new window of X-ray polarimetry of AGN through IXPE observations. We will delve into two primary areas of interest: first, the magnetic field geometry and particle acceleration mechanisms in the jets of radio-loud AGN, such as blazars, where the relativistic acceleration process dominates the spectral energy distribution; and second, the geometry of the hot corona in radio-quiet AGN. Thus far, the IXPE results from blazars favor the energy-stratified shock acceleration model, and they provide evidence of helical magnetic fields inside the jet. Concerning the corona geometry, the IXPE results are consistent with a disk-originated slab-like or wedge-like shape, as could result from Comptonization around the accretion disk.

The Helicity of Magnetic Fields Associated with Relativistic Electron Vortex Beams

The Helicity of Magnetic Fields Associated with Relativistic Electron Vortex Beams

Topological band structure due to modified Kramers degeneracy for electrons in a helical magnetic field

Topological band structure due to modified Kramers degeneracy for electrons in a helical magnetic field

Evolution of Magnetic Field of the Quasar 1604+159 at parsec Scale

We have analyzed the total intensity, spectral index, linear polarization, and rotation measure (RM) distributions at the parsec scale for the quasar 1604+159. The source was observed at 5.0, 8.4, and 15.4 GHz in 2002 and 4.6, 5.1, 6.0, 7.8, 12.2, 15.2, and 43.9 GHz in 2020 with the American Very Long Baseline Array (VLBA). Combining the polarization results of Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments at 15 GHz from 2009 to 2013, we studied the evolution of magnetic field at the parsec scale for the source. We detected a core-jet structure. The jet extends to the distance of ∼25 mas from the core at a direction of ∼66° north by east. The shape of the jet derived from 15 GHz data varies slightly with time and could be described by a straight line. Based on the linear polarization distribution in 2002, we divided the source structure into the central region and the jet region. In the jet region, we find the polarized emission varies with time. The flatter spectral index values and electric vector position angle direction indicate the possible existence of shocks, contributing to the variation of polarization in the jet with time. In the central region, the derived core shift index k r values indicate that the core in 2002 is close to the equipartition case, while it deviated from the case in 2020. The measured magnetic field strength in 2020 is 2 orders of magnitude lower than that in 2002. We detected transverse RM gradients, evidence of a helical magnetic field, in the core. The polarized emission orients in general toward the jet direction in the core. At 15 GHz, in the place close to the jet base, the polarization direction changes significantly with time from perpendicular to parallel to the jet direction. The evolution of RM and magnetic field structure are potential reasons for the observed polarization change. The core ∣RM∣ in 2020 increases with frequency following a power law with index a = 2.7 ± 0.5, suggesting a fast electron density falloff in the medium with distance from the jet base.

Unveiling the bent-jet structure and polarization of OJ 287 at 1.7 GHz with space VLBI

We present total intensity and linear polarization images of OJ 287 at 1.68 GHz, obtained through space-based very long baseline interferometry (VLBI) observations with RadioAstron on April 16, 2016. The observations were conducted using a ground array consisting of the Very Long Baseline Array (VLBA) and the European VLBI Network (EVN). Ground-space fringes were detected with a maximum projected baseline length of ∼5.6 Earth’s diameter, resulting in an angular resolution of ∼530 μas. With this unprecedented resolution at such a low frequency, the progressively bending jet structure of OJ 287 has been resolved up to ∼10 parsec of the projected distance from the radio core. In comparison with close-in-time VLBI observations at 15, 43, 86 GHz from MOJAVE and VLBA-BU-BLAZAR monitoring projects, we obtain the spectral index map showing the opaque core and optically thin jet components. The optically thick core has a brightness temperature of ∼1013 K, and is further resolved into two sub-components at higher frequencies labeled C1 and C2. These sub-components exhibit a transition from optically thick to thin, with a synchrotron self-absorption (SSA) turnover frequency estimated to be ∼33 and ∼11.5 GHz, and a turnover flux density ∼4 and ∼0.7 Jy, respectively. Assuming a Doppler boosting factor of 10, the SSA values provide the estimate of the magnetic field strengths from SSA of ∼3.4 G for C1 and ∼1.0 G for C2. The magnetic field strengths assuming equipartition arguments are also estimated as ∼2.6 G and ∼1.6 G, respectively. The integrated degree of linear polarization is found to be approximately ∼2.5%, with the electric vector position angle being well aligned with the local jet direction at the core region. This alignment suggests a predominant toroidal magnetic field, which is in agreement with the jet formation model that requires a helical magnetic field anchored to either the black hole ergosphere or the accretion disk. Further downstream, the jet seems to be predominantly threaded by a poloidal magnetic field.

Confinement of transitioning particles in bi-helical Wendelstein-type configurations

Recently, stochastic motion of 3.5-MeV alpha particles with orbits that vary between locally trapped and locally passing states (transitioning particles) in a Helias reactor was observed numerically. This validated the theoretical predictions that (i) the stochastic diffusion represents a mechanism of considerable delayed loss of fast ions in quasi-isodynamic stellarators and (ii) it is possible to prevent the escape of particles to the wall by closing the separatrix between the locally trapped and passing states. It was concluded that, in principle, the separatrix could be made closed, resulting in a reduction of fast ion losses, by compensating for the effect of the helical component of the magnetic field $(1, 1)$ with an enhanced ‘anti-helical’ harmonic $(1, -1)$ ; the enlargement of this harmonic was proposed previously for other reasons. This possibility is explored in this work. Equations of previous relevant works were generalised to include the $(1, -1)$ harmonic. Calculations were carried out for several magnitudes of the ratio of anti-helical to helical magnetic field harmonics. Positive effects were found already at the smallest anti-helical harmonic considered: when the latter ratio is 0.25, transitioning particles with the smallest and intermediate pitch parameters are confined and, moreover, their fraction decreased. When the ratio is 0.85, almost all transitioning particles are confined and their fraction is minimal; well-confined localised orbits dominate at the smallest pitch parameters.

Jump-starting Relativistic Flows and the M87 Jet

We point out the dominant importance of plasma injection effects of relativistic winds from pulsars and black holes. We demonstrate that outside the light cylinder, the magnetically dominated outflows sliding along the helical magnetic field move nearly radially with very large Lorentz factors, γ 0 ≫ 1, imprinted into the flow during pair production within the gaps. Only at larger distances, r ≥ γ 0(c/Ω), does MHD acceleration Γ ∝ r take over. As a result, Blandford–Znajek (BZ)-driven outflows produce spine-brightened images. The best-resolved case of the jet in M87 shows both edge-brightened features, as well as weaker spine-brightened features. Only the spine-brightened component can be BZ driven/originate from the black hole's magnetosphere.

Mathematical Modeling of Plasma Transport in a Helical Magnetic Field

Mathematical Modeling of Plasma Transport in a Helical Magnetic Field

SIMULATIONS OF LINEAR POLARIZATION OF PRECESSING AGN JETS AT PARSEC SCALES

The latest results of the most detailed analysis of multi-epoch polarization-sensitive observations of active galactic nuclei (AGN) jets at parsecs scales by very long baseline interferometry (VLBI) reveal several characteristic patterns of linear polarization distribution and its variability [1, 2]. Some of the observed profiles can be reproduced by a simple model of a jet threaded by a helical magnetic field. However, none of the models presented to date can explain the observed polarization profiles with an increase in its degree towards the edges of the jet, and accompanied by a “fountain” type electrical vector pattern and its high temporal variability in the center. Based on simulations of the VLBI observations of relativistic jets, we show here that the observed transverse linear polarization profiles, atypical for the simple magnetic field models can be naturally produced assuming the finite resolution of VLBI arrays and precession of a jet on ten-years scales, observational indications of which are found in an increasing number of AGN. In our simulations, we qualitatively reproduce the distribution of the electric vector and its variability, though the polarization images are characterized by a bright spine due to weak smearing, which is poorly consistent with observations. More effective depolarization can be obtained in models with the suppressed emission of the jet spine.

Helical magnetic fields and semi-classical asymptotics of the lowest eigenvalue

We study the three-dimensional Neumann magnetic Laplacian in the presence of a semiclassical parameter and a non-uniform magnetic field with constant intensity. We determine a sharp two term asymptotics for the lowest eigenvalue, where the second term involves a quantity related to the magnetic field and the geometry of the domain. In the special case of the unit ball and a helical magnetic field, the concentration takes place on two symmetric points of the unit sphere.

Mathematical model of matter transfer in a helical magnetic field using boundary conditions at infinity

The paper presents a mathematical model of plasma transfer in an open magnetic trap using the condition of zero plasma concentration at infinity. New experimental data obtained at the SMOLA trap at the Budker Institute of Nuclear Physics SB RAS were used. Plasma confinement in the plant is carried out by transmitting a pulse from a magnetic field with helical symmetry to a rotating plasma. The mathematical model is based on a stationary plasma transfer equation in an axially symmetric formulation. The stationary equation of the transfer of matter contains second spatial derivatives. The optimal template for the approximation of the mixed derivative based on the test problem is selected. The numerical implementation of the model by the establishment method and the method of successive over-relaxation is compared.

Properties of the jet in M87 revealed by its helical structure imaged with the VLBA at 8 and 15 GHz

ABSTRACT We present full-track high-resolution radio observations of the jet of the galaxy M87 at 8 and 15 GHz. These observations were taken over three consecutive days in 2009 May using the Very Long Baseline Array (VLBA), one antenna of the Very Large Array (VLA), and the Effelsberg 100 m telescope. Our produced images have dynamic ranges exceeding 20 000:1 and resolve linear scales down to approximately 100 Schwarzschild radii, revealing a limb-brightened jet and a faint, steep spectrum counter-jet. We performed jet-to-counter-jet analysis, which helped estimate the physical parameters of the flow. The rich internal structure of the jet is dominated by three helical threads, likely produced by the Kelvin–Helmholtz (KH) instability developing in a supersonic flow with a Mach number of approximately 20 and an enthalpy ratio of around 0.3. We produce a clean imaging bias-corrected 8–15 GHz spectral index image, which shows spectrum flattening in regions of helical thread intersections. This further supports the KH origin of the observed internal structure of the jet. We detect polarized emission in the jet at distances of approximately 20 milliarcseconds from the core and find Faraday rotation which follows a transverse gradient across the jet. We apply Faraday rotation correction to the polarization position angle and find that the position angle changes as a function of distance from the jet axis, which suggests the presence of a helical magnetic field.

Intrinsic Design and Modulated Circular Dichroism of Inorganic Nanowire/Hydrogel Composite

AbstractControlling the handedness and absorptive characteristics of chiral materials is essential for exploring new advances in the field of chiral sensors and catalysts. The deliberate architecture of the building blocks and their self‐assembly process are critical factors for fabricating chirally active structures from achiral nanoscale components. Herein, the fabrication of multicomponent gel structures comprising magnetoplasmonic core–shell Au@FexOy nanowires embedded in a macroscopic titania nanocrystal network is demonstrated, which shows broadband absorption covering the ultraviolet–visible light spectrum while maintaining excellent porosity in the aerogel state. The effect of externally applied helical magnetic field is exploited to induce self‐assembly of the magnetoplasmonic nanowires into chirally active superstructures. Furthermore, a second vector of symmetry is observed when the chiral hydrogel unit is rotated up to 45° around the z‐axis perpendicular to the light path, in which the measured circular dichroism intensity is modulated up to ±102% compared to those at 0°. This study serves as a concept of designing optically active chiral 3D superstructures, applicable to optical filters, sensing devices, and chiral photocatalysts.

Baryogenesis from decaying magnetic helicity in axiogenesis

Generating axion dark matter through the kinetic misalignment mechanism implies the generation of large asymmetries for Standard Model fermions in the early universe. Even if these asymmetries are washed out at later times, they can trigger a chiral plasma instability in the early universe. Similarly, a direct coupling of the axion with the hypercharge gauge field can trigger a tachyonic instability. These instabilities produce helical magnetic fields, which are preserved until the electroweak phase transition. At the electroweak phase transition, these become a source of baryon asymmetry, which can be much more efficient than the original axiogenesis proposal. We discuss constraints on axion dark matter production from the overproduction of the baryon asymmetry as well as a minimal, albeit fine-tuned setup, where both the correct dark matter abundance and baryon asymmetry can be achieved. For a given axion decay constant, this leads to a sharp prediction for the mass of the radial direction of the Peccei Quinn field, which is a soft mass scale in supersymmetric theories.