Unipolar Induction Research Articles

Unipolar induction hypothesis testing experiment

The phenomenon of unipolar induction is closely related to the problem of electrodynamics of rotating reference frames. Attempts to apply the general relativity theory to construct the electrodynamics of rotating systems have not yet led to a universally recognised theory. Various authors derive different systems of electrodynamics equations in rotating reference frames and different models of the electric field of a rotating magnet. These models can be tested in experiments with rotating magnets. In this work, an experiment is performed to test two models of the electric field of a rotating magnetised sphere. The theoretical models predict different values of the electric potential of unipolar induction at the pole and equator of the sphere relative to infinity. In the experiment, direct measurements of the potential of the pole and equator of a rotating magnetised sphere relative to a grounded screen are performed. The experimental results contradict the quadrupole model and correspond to the electric field model obtained by applying Lorenz transformations for the field vectors both inside and outside the sphere.

Comparison of different models for gravitational and electromagnetic radiation of binary neutron star mergers

The neutron star binary merger is one of the most energetic phenomena in our Universe. Based on the calculation of gravitational radiation (GR) with the separate consideration of revolution and stellar rotation, and electromagnetic radiation (ER) with unipolar induction DC circuit model and magnetic dipole model, the results are compared to analyse the extent to which the stellar rotation will affect the total gravitational radiation power. Besides, the relationships between radiation power and the related parameters (e.g., orbital radius and stellar mass) are investigated. Furthermore, the feasibility of different types of binary star merger as the progenitor of fast radio bursts and gamma-ray bursts were studied based on the two models of ER, obtaining that binary neutron star and neutron star-white dwarf systems are among the possible progenitors. Finally, the radiation power of both GR and ER are compared under the same conditions. According to the results, the energy dissipation of the system is dominated by gravitational radiation. These results shed lights on further studies on the radiation processes of binary neutron star mergers and binary star systems.

The Solar Wind Interaction with (1) Ceres: The Role of Interior Conductivity

As a potential “ocean world,” (1) Ceres’ interior may possess relatively high electrical conductivities on the order of 10−4–100 S m−1, suggesting that the solar wind interaction with Ceres may differ from other highly resistive objects such as the Moon. Here, we use a hybrid plasma model to quantify the solar wind interaction with Ceres over a range of scenarios for Ceres’ internal conductivity structure and the upstream solar wind and interplanetary magnetic field (IMF) conditions. Internal models for Ceres include one-, two-, and three-layer conductivity structures that variously include a crust, mantle, and/or subsurface ocean, while modeled solar wind conditions include a nominal case, a high IMF case, and an “extreme” space weather case. To first order, Ceres’ interaction with the solar wind is governed by the draping and enhancement of the IMF over its interior, whether from a moderate-conductivity mantle or a high-conductivity ocean. In turn, IMF draping induces compressional wings in the solar wind density and deceleration in the solar wind speed outside of Ceres. Together, all three effects are readily observable by a hypothetical orbital or landed mission with standard plasma and magnetic field instrumentation. Finally, we also consider the possible effects of unipolar induction within Ceres, which has been previously suggested as a mechanism for conducting bodies in the solar wind. Our model results show that the efficacy of unipolar induction is highly suppressed by the slow magnetic field-line diffusion through Ceres’ interior and, thus, is not a significant contributor to Ceres’ overall interaction with the solar wind.

Orbital Decay of Double White Dwarfs: Beyond Gravitational-wave Radiation Effects

The traditional description of the orbital evolution of compact-object binaries, like double white dwarfs (DWDs), assumes that the system is driven only by gravitational-wave (GW) radiation. However, the high magnetic fields with intensities of up to gigagausses measured in WDs alert a potential role of the electromagnetic (EM) emission in the evolution of DWDs. We evaluate the orbital dynamics of DWDs under the effects of GW radiation, tidal synchronization, and EM emission by a unipolar inductor generated by the magnetic primary and the relative motion of the nonmagnetic secondary. We show that the EM emission can affect the orbital dynamics for magnetic fields larger than megagausses. We applied the model to two known DWDs, SDSS J0651+2844 and ZTF J1539+5027, for which the GW radiation alone does not fully account for the measured orbital decay rate. We obtain upper limits to the primary’s magnetic field strength, over which the EM emission causes an orbital decay faster than observed. The contribution of tidal locking and the EM emission is comparable, and together they can contribute up to 20% to the measured orbital decay rate. We show that the gravitational waveform for a DWD modeled as purely driven by GWs and including tidal interactions and EM emission can have large relative dephasing detectable in the mHz regime of frequencies relevant for space-based detectors like LISA. Therefore, including physics besides GW radiation in the waveform templates is essential to calibrate the GW detectors using known sources, e.g., ZTF J1539+5027, and to infer binary parameters.

Resolving the paradox of unipolar induction: new experimental evidence on the influence of the test circuit

A novel experiment has been devised shedding new light on the phenomenon of unipolar induction, also known as “Faraday’s Paradox”. This is a topic which continues to fascinate scientists and engineers with much debate continuing to this day. In particular, the question of the field co-rotating with the magnet or remaining stationary remains unsettled and supporting evidence exists for both positions. In this study, we present a novel experimental apparatus that includes, for the first time, the relative motion of the measurement circuit including the closing wires, as well as the magnet and disc respectively. The results show that the closing wire needs to be considered as part of the problem, which enables the apparent paradox associated with this phenomenon to be resolved. However, it remains impossible to tell if the field co-rotates with the magnet or if it remains stationary. Instead, direct electron interaction is considered as a viable alternative to resolve remaining paradoxes.

Mathematical-Physical Approach to Prove that the Navier-‎Stokes Equations Provide a Correct Description of Fluid ‎Dynamics

This publication takes a mathematical approach to a general solution to the Navier-Stokes equations. The basic idea is a ‎mathematical analysis of the unipolar induction according to Faraday with the help of the vector analysis. The vector analysis ‎enables the unipolar induction and the Navier-Stokes equations to be related physically and mathematically since both ‎formulations are mathematically equivalent. Since the unipolar induction has proven itself in practice, it can be used as a ‎reference for describing the Navier-Stokes equations‎.

Magnetospheres of black hole-neutron star binaries

We perform force-free simulations for a neutron star orbiting a black hole, aiming at clarifying the main magnetosphere properties of such binaries towards their innermost stable circular orbits. Several configurations are explored, varying the orbital separation, the individual spins and misalignment angle among the magnetic and orbital axes. We find significant electromagnetic luminosities, $L\sim 10^{42-46} \, [B_{\rm pole}/ 10^{12}{\rm G}]^2 \, {\rm erg/s}$ (depending on the specific setting), primarily powered by the orbital kinetic energy, being about one order of magnitude higher than those expected from unipolar induction. The systems typically develop current sheets that extend to long distances following a spiral arm structure. The intense curvature of the black hole produces extreme bending on a particular set of magnetic field lines as it moves along the orbit, leading to magnetic reconnections in the vicinity of the horizon. For the most symmetric scenario (aligned cases), these reconnection events can release large-scale plasmoids that carry the majority of the Poynting fluxes. On the other hand, for misaligned cases, a larger fraction of the luminosity is instead carried outwards by large-amplitude Alfv{\'e}n waves disturbances. We estimate possible precursor electromagnetic emissions based on our numerical solutions, finding radio signals as the most promising candidates to be detectable within distances of $\lesssim 200$\,Mpc by forthcoming facilities like the Square Kilometer Array.

On the Causes of the Slow Solar Wind: 1. The Solar Unipolar Induction Currents

AbstractThe cause of the solar wind is sought on a large‐scale (J × B) force resulting from the solar unipolar induction current, rather than coronal heating and small‐scale processes in the corona. In this paper, we consider the unipolar induction system considered by Alfven (1981, https://doi.org/10.1007/978-94-009-8374-8) the polar current (1.5 × 109 A) flowing out from the polar region of the sun spreads down longitudinally, which produces azimuthal magnetic fields. We considered two models, A and B. In Model A, the current spreads down fairly uniform in five divided regions of the heliosphere (rather than flowing only along the outer surface of the heliosphere). The resulting (J × B) force is mainly directed outward, causing an outward flow of the heliospheric plasmas. However, in this case, the speed at a distance of 1 AU is only 1 km/s, although the acceleration in each divided region is much greater than the solar gravity. In Model B, one third of the dynamo current is assumed to be concentrated in the area between 9.5 and 10.5 (where denotes the solar radius) and B = 10−6 T (103 nT) at 10 . The acceleration is estimated to be 1.4 × 102 m/s2 and the resulting speed at 1 AU is 200 km/s. Therefore, there is a possibility that the solar unipolar induction provides partially a new possibility for the cause of a slow, bulk flow of the solar wind.

Multimessenger Signals from Black Hole–Neutron Star Mergers without Significant Tidal Disruption

Abstract We study the multimessenger signals from the merger of a black hole with a magnetized neutron star using resistive magnetohydrodynamics simulations coupled to full general relativity. We focus on a case with a 5:1 mass ratio, where only a small amount of the neutron star matter remains post-merger, but we nevertheless find that significant electromagnetic radiation can be powered by the interaction of the neutron star’s magnetosphere with the black hole. In the lead-up to merger, strong twisting of magnetic field lines from the inspiral leads to plasmoid emission and results in a luminosity in excess of that expected from unipolar induction. We find that the strongest emission occurs shortly after merger during a transitory period in which magnetic loops form and escape the central region. The remaining magnetic field collimates around the spin axis of the remnant black hole before dissipating, an indication that, in more favorable scenarios (higher black hole spin/lower mass ratio) with larger accretion disks, a jet would form.

A test of the planet–star unipolar inductor for magnetic white dwarfs

ABSTRACT Despite thousands of spectroscopic detections, only four isolated white dwarfs exhibit Balmer emission lines. The temperature inversion mechanism is a puzzle over 30 years old that has defied conventional explanations. One hypothesis is a unipolar inductor that achieves surface heating via ohmic dissipation of a current loop between a conducting planet and a magnetic white dwarf. To investigate this model, new time-resolved spectroscopy, spectropolarimetry, and photometry of the prototype GD 356 are studied. The emission features vary in strength on the rotational period, but in antiphase with the light curve, consistent with a cool surface spot beneath an optically thin chromosphere. Possible changes in the line profiles are observed at the same photometric phase, potentially suggesting modest evolution of the emission region, while the magnetic field varies by 10 per cent over a full rotation. These comprehensive data reveal neither changes to the photometric period, nor additional signals such as might be expected from an orbiting body. A closer examination of the unipolar inductor model finds points of potential failure: the observed rapid stellar rotation will inhibit current carriers due to the centrifugal force, there may be no supply of magnetospheric ions, and no antiphase flux changes are expected from ohmic surface heating. Together with the highly similar properties of the four cool, emission-line white dwarfs, these facts indicate that the chromospheric emission is intrinsic. A tantalizing possibility is that intrinsic chromospheres may manifest in (magnetic) white dwarfs, and in distinct parts of the Hertzsprung–Russell diagram based on structure and composition.

Charging and Electromagnetic Radiation during the Inspiral of a Black Hole–Neutron Star Binary

Abstract Because mergers of black hole–neutron star (BH–NS) binaries are widely argued to produce both gravitational and electromagnetic waves, these binaries are among the most attractive systems in the era of multi-messenger astronomy. In this paper we explore the charging processes of a moving BH in two types of charged surroundings and propose a new charging scenario differing from the elegant mechanism of Wald. During the inspiral of such a binary, the NS is strongly magnetized and the BH is moving inward. By considering this moving BH charging scenario, we find that the BH will increasingly accumulate enough net charge to light up the binary system at the inspiral stage. This charging process is universal no matter whether the BH spins or not. We show that our BH charging scenario can physically explain the BH’s unipolar inductor mechanism in a BH–NS binary system. We calculate electromagnetic emission luminosities due to various energy dissipation mechanisms and find that the electric dipole radiation of the BH makes a dominant contribution to electromagnetic emission at the final stage of inspiral if the BH spins slowly.

Unimodal electric motor-generator

The commissioning of nuclear power plants in Belarus sets out wide tasking for the efficient usage of electrical energy in various electrical systems, instruments and devices. Specifically, it concerns the stationary and special-purpose electric motors. At present, they use bipolar motors with a collector – the switch of the motor armature windings during its rotation. However, there is a completely different type of motors that does not require a collector – the unipolar electric motor-generator. Some of its properties allow it to be used where the commutator motor is unsuitable, for example, in explosive and fire hazardous environments (sparking on the collector is unacceptable), in precision devices where extreme smoothness and vibration lack are required, etc. Physico-mathematical foundations of the unipolar motor-generator (moving media electrodynamics, Lorentz force, unipolar induction, magnetohydrodynamics) are described in a number of monographs and textbooks, for example, in [1–4]. The purpose of this article is to pay attention to the technical feasibility of the unipolar motor-generator in a design with separated conductors in the rotor drum.

Single magnetic white dwarfs with Balmer emission lines: a small class with consistent physical characteristics as possible signposts for close-in planetary companions

ABSTRACT We report the identification of SDSS J121929.45+471522.8 as the third apparently isolated magnetic (B ≃ 18.5 ± 1.0 MG) white dwarf exhibiting Zeeman-split Balmer emission lines. The star shows coherent variability at optical wavelengths with an amplitude of ≃0.03 mag and a period of 15.26 h, which we interpret as the spin period of the white dwarf. Modelling the spectral energy distribution and Gaia parallax, we derive a white dwarf temperature of 7500 ± 148 K, a mass of 0.649 ± 0.022 M⊙, and a cooling age of 1.5 ± 0.1 Gyr, as well as an upper limit on the temperature of a sub-stellar or giant planet companion of ≃250 K. The physical properties of this white dwarf match very closely those of the other two magnetic white dwarfs showing Balmer emission lines: GD356 and SDSS J125230.93−023417.7. We argue that, considering the growing evidence for planets and planetesimals on close orbits around white dwarfs, the unipolar inductor model provides a plausible scenario to explain the characteristics of this small class of stars. The tight clustering of the three stars in cooling age suggests a common mechanism switching the unipolar inductor on and off. Whereas Lorentz drift naturally limits the lifetime of the inductor phase, the relatively late onset of the line emission along the white dwarf cooling sequence remains unexplained.

An Isolated White Dwarf with 317 s Rotation and Magnetic Emission

Abstract We report the discovery of short-period photometric variability and modulated Zeeman-split hydrogen emission in SDSSJ125230.93−023417.72 (EPIC 228939929), a variable white dwarf star observed at long cadence in K2 Campaign 10. The behavior is associated with a magnetic (B = 5.0 MG) spot on the stellar surface, making the 317.278 s period a direct measurement of the stellar rotation rate. This object is therefore the fastest-rotating, apparently isolated (without a stellar companion) white dwarf yet discovered and the second found to exhibit chromospheric Balmer emission after GD 356, in which the emission has been attributed to a unipolar inductor mechanism driven by a possible rocky planet. We explore the properties and behavior of this object, and consider whether its evolution may hold implications for white dwarf mergers and their remnants.

Magnetic fields in isolated and interacting white dwarfs

The magnetic white dwarfs (MWDs) are found either isolated or in interacting binaries. The isolated MWDs divide into two groups: a high field group (105–109 G) comprising some 13±4% of all white dwarfs (WDs), and a low field group (B<105 G) whose incidence is currently under investigation. The situation may be similar in magnetic binaries because the bright accretion discs in low field systems hide the photosphere of their WDs thus preventing the study of their magnetic fields’ strength and structure. Considerable research has been devoted to the vexed question on the origin of magnetic fields. One hypothesis is that WD magnetic fields are of fossil origin, that is, their progenitors are the magnetic main-sequence Ap/Bp stars and magnetic flux is conserved during their evolution. The other hypothesis is that magnetic fields arise from binary interaction, through differential rotation, during common envelope evolution. If the two stars merge the end product is a single high field MWD. If close binaries survive and the primary develops a strong field, they may later evolve into the magnetic cataclysmic variables (MCVs). The recently discovered population of hot, carbon-rich WDs exhibiting an incidence of magnetism of up to about 70% and a variability from a few minutes to a couple of days may support the merging binary hypothesis. The fields in the low field MWDs may instead arise from a dynamo mechanism taking place in convective zones during post main-sequence evolution. Should this be the case, there may be a field strength below which all WDs are magnetic and thus fields are expected to always play a role in accretion processes in close binaries. Several studies have raised the possibility of the detection of planets around MWDs. Rocky planets may be discovered by the detection of anomalous atmospheric heating of the MWD when the unipolar inductor mechanism operates whilst large gaseous planets may reveal themselves through cyclotron emission from wind-driven accretion onto the MWD. Planetary remains have recently revealed themselves in the atmospheres of about 25% of WDs that are polluted by elements such as Ca, Si, and often also Mg, Fe, Na. This pollution has been explained by ongoing accretion of planetary debris. Interestingly, the incidence of magnetism is approximately 50% in cool, hydrogen-rich, polluted WDs, suggesting that these fields may be related to differential rotation induced by some super-Jupiter bodies that have plunged into the WD. The study of isolated and accreting MWDs is likely to continue to yield exciting discoveries for many years to come.

Synthesis of 3D Models of a Unipolar Inductor Machine

Like-pole reluctance machines with one or more permanent magnets on a rotor, which create net excitation that is closed in the axial–radial direction, are analyzed. Design practices are developed for them that have to be checked via basic methods. One such method is the finite-element technique, or grid method. However, it cannot be applied in the form of a two-dimensional model for the structure under analysis. Hence, a method is presented for constructing three-dimensional models of unipolar inductor machines. The construction is performed by extruding (pressing out) areas of the sector, which outline tooth or pole partition in a plane that is perpendicular to the axis of rotation, coated with projections of boundaries of all axially placed cylindrical sections of the same cutset within each section, forming a 3D model of a stator or a rotor. The method is designed for subsequent mesh generation and for calculation by means of the finite-element method related to magnetic scalar potentials, followed by determination of energy gain and rotating electromagnetic torque, defined by change of a magnetic field energy before and after the rotor is rotated by some basic angle. The described method of creating 3D models is also studied in application to like-pole machines with electromagnetic excitation on the part of a stator. In addition, it is applicable to creating models intended for examining leakage fields in the sphere of the front parts of machines by ordinary geometry reduced to a two-dimensional one.

Jet in jet in M87

New high-resolution Very Long Baseline Interferometer observations of the prominent jet in the M87 radio galaxy show a persistent triple-ridge structure of the transverse 15-GHz profile with a previously unobserved ultra-narrow central ridge. This radio structure can reflect the intrinsic structure of the jet, so that the jet as a whole consists of two embedded coaxial jets. A relativistic magnetohydrodynamic model is considered in which an inner jet is placed inside a hollow outer jet and the electromagnetic fields, pressures and other physical quantities are found. The entire jet is connected to the central engine that plays the role of a unipolar inductor generating voltage between the jets and providing opposite electric currents, and the charge neutrality and current closure together with the electromagnetic fields between the jets can contribute to the jet stabilization. The constant voltage is responsible for the similar widening laws observed for the inner and outer jets. This jet-in-jet structure can indicate simultaneous operation of two different jet-launching mechanisms, one relating to the central supermassive black hole and the other to the surrounding accretion disc. An inferred magnetic field of 80 G at the base is sufficient to provide the observed jet luminosity.

Neutrino lighthouse powered by SagittariusA*disk dynamo

We show that the subset of high energy neutrino events detected by IceCube which correlate with the Galactic center (within uncertainties of their reconstructed arrival directions) could originate in the collisions of protons accelerated by the Sagittarius (Sgr) A* disk dynamo. Under very reasonable assumptions on source parameters we demonstrate that the supermassive black hole at the center of the Galaxy could launch protons and nuclei with multi PeV energies. Acceleration of these particles in a period of seconds up to Lorentz factors of \sim 10^7 is possible by means of the Blandford-Znajek mechanism, which wires the spinning magnetosphere of Sgr A* as a Faraday unipolar inductor. During the acceleration process the \sim PeV progenitors of \sim 50 TeV neutrinos radiate curvature photons in the keV energy range. We show that IceCube neutrino astronomy with photon tagging on the Chandra X-ray Observatory could provide a valuable probe for the Blandford-Znajek acceleration mechanism. We also argue that EeV neutrinos, which may be produced in a similar fashion during the merging of binary black holes, could become the smoking gun for particle acceleration in a one-shot boost.

FAST RADIO BURSTS FROM THE INSPIRAL OF DOUBLE NEUTRON STARS

ABSTRACT In this Letter, we propose that a fast radio burst (FRB) could originate from the magnetic interaction between double neutron stars (NSs) during their final inspiral within the framework of a unipolar inductor model. In this model, an electromotive force is induced on one NS to accelerate electrons to an ultra-relativistic speed instantaneously. We show that coherent curvature radiation from these electrons moving along magnetic field lines in the magnetosphere of the other NS is responsible for the observed FRB signal, that is, the characteristic emission frequency, luminosity, duration, and event rate of FRBs can be well understood. In addition, we discuss several implications of this model, including double-peaked FRBs and possible associations of FRBs with short-duration gamma-ray bursts and gravitational-wave events.

The magnetic properties of the star Kepler-78

Kepler-78 is host to a transiting 8.5-hour orbit super-Earth. In this paper, the rotation and magnetic properties of the planet host star are studied. We first revisit the Kepler photometric data for a detailed description of the rotation properties of Kepler-78, showing that the star seems to undergo a cycle in the spot pattern of ~1,300 day duration. We then use spectropolarimetric observations with CFHT/ESPaDOnS to measure the circular polarization in the line profile of the star during its rotation cycle, as well as spectroscopic proxies of the chromospheric activity. The average field has an amplitude of 16 G. The magnetic topology is characterized by a poloidal and a toroidal component, encompassing 60% and 40% of the magnetic energy, respectively. Differential rotation is detected with an estimated rate of 0.105+-0.039 rad/d. Activity tracers vary with the rotation cycle of the star; there is no hint that a residual activity level is related to the planetary orbit at the precision of our data. The description of the star magnetic field's characteristics then may serve as input for models of interactions between the star and its close-by planet, e.g., Ohmic dissipation and unipolar induction.