scholarly journals An 84-μG Magnetic Field in a Galaxy at Z=0.692?

2008 ◽  
Vol 4 (S254) ◽  
pp. 95-96
Author(s):  
Arthur M. Wolfe ◽  
Regina A. Jorgenson ◽  
Timothy Robishaw ◽  
Carl Heiles ◽  
Jason X. Prochaska
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Dynamo Model ◽  
Magnetic Field Generation ◽  
Interstellar Gas ◽  
Splitting Technique ◽  
Average Value ◽  
The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

scholarly journals Modes of magnetic field generation in the low-mode αΩ-dynamo model with dynamic regulation of the α-effect by the field energy

2021 ◽  
pp. 92-103
Author(s):  
О.В. Шереметьева
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Damping Coefficient ◽  
Dynamo Model ◽  
Field Energy ◽  
Magnetic Field Generation ◽  
Dynamic Regulation ◽  
Field Generation ◽  
Mhd System ◽  
The Magnetic Field

В работе используется маломодовая модель αΩ-динамо для моделирования режимов генерации магнитного поля при незначительных изменениях поля скорости вязкой жидкости. В рамках этой модели интенсивность α-эффекта регулируется процессом с памятью, который вводится в магнитогидродинамическую систему (МГД-система) как аддитивная поправка в виде функционала Z(t) от энергии поля. В качестве ядра J(t) функционала Z(t) выбрана функция, определяющая затухающие колебания с варьируемым коэффициентом затухания и постоянной частотой затухания, принятой равной единице. Исследование поведения магнитного поля проводится на больших временных масштабах, поэтому для численных расчётов используется перемасштабированная и обезразмеренная МГД-система, где в качестве единицы времени принято время диссипации магнитного поля (104 лет). Управляющими параметрами системы выступают число Рейнольдса и амплитуда α-эффекта, в которых заложена информация о крупномасштабном и турбулентном генераторах. Результаты численного моделирования режимов генерации магнитного поля при различных значениях коэффициента затухания и постоянной частоте затухания отражены на фазовой плоскости управляющих параметров. В работе исследуется вопрос о динамике изменения картины на фазовой плоскости в зависимости от значения коэффициента затухания. Проводится сравнение с результатами, полученными ранее при постоянной интенсивности α-эффекта и при изменении интенсивности α — эффекта, которое определялось функционалом Z(t) с показательным ядром и аналогичными значениями коэффициента затухания. In this paper, we use a low-mode αΩ-dynamo model to simulate the modes of magnetic field generation with insignificant changes in the velocity field of a viscous fluid. Within the framework of this model, an additive correction is introduced into the magnetohydrodynamic system to control the intensity of the α-effect in the form of a function Z(t) from the field energy. As the kernel J(t) of the function Z(t) is chosen the function that determines damped oscillations with the different values of the damping coefficient and a constant damping frequency taken equal to one. The study of the magnetic field behavior is carried out on a large time scales, therefore, for numerical calculations, a rescaled and dimensionless MHD-system is used, where the time of the magnetic field dissipation (104 years) is accepted as the unit of time. The main parameters of the system are the Reynolds number and the amplitude of the α-effect, which contains information about the large-scale and turbulent generators, respectively. According to the results of numerical simulation, an increase in the values of the damping coefficient is characterized an increase in the inhibition effect of the process Z(t) on the α-effect and decrease of the magnetic field divergence region on the plane of the main parameters.

scholarly journals No-z Model for Magnetic Fields of Different Astrophysical Objects and Stability of the Solutions

Data ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 4
Author(s):  
Evgeny Mikhailov ◽  
Daniela Boneva ◽  
Maria Pashentseva
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Point Of View ◽  
Accretion Discs ◽  
Wide Range ◽  
Astrophysical Objects ◽  
Alpha Effect ◽  
The Stability ◽  
The Magnetic Field

A wide range of astrophysical objects, such as the Sun, galaxies, stars, planets, accretion discs etc., have large-scale magnetic fields. Their generation is often based on the dynamo mechanism, which is connected with joint action of the alpha-effect and differential rotation. They compete with the turbulent diffusion. If the dynamo is intensive enough, the magnetic field grows, else it decays. The magnetic field evolution is described by Steenbeck—Krause—Raedler equations, which are quite difficult to be solved. So, for different objects, specific two-dimensional models are used. As for thin discs (this shape corresponds to galaxies and accretion discs), usually, no-z approximation is used. Some of the partial derivatives are changed by the algebraic expressions, and the solenoidality condition is taken into account as well. The field generation is restricted by the equipartition value and saturates if the field becomes comparable with it. From the point of view of mathematical physics, they can be characterized as stable points of the equations. The field can come to these values monotonously or have oscillations. It depends on the type of the stability of these points, whether it is a node or focus. Here, we study the stability of such points and give examples for astrophysical applications.

scholarly journals Connecting magnetic fields from sub-galactic scale to clusters of galaxies and beyond with cosmological MHD simulations

2015 ◽  
Vol 11 (A29B) ◽  
pp. 699-699
Author(s):  
Klaus Dolag ◽  
Alexander M. Beck ◽  
Alexander Arth
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Heat Transport ◽  
Galaxy Clusters ◽  
Large Scale ◽  
High Redshift ◽  
Galactic Halos ◽  
Rotation Measure ◽  
The Magnetic Field ◽  
Good Agreement

AbstractUsing the MHD version of Gadget3 (Stasyszyn, Dolag & Beck 2013) and a model for the seeding of magnetic fields by supernovae (SN), we performed simulations of the evolution of the magnetic fields in galaxy clusters and study their effects on the heat transport within the intra cluster medium (ICM). This mechanism – where SN explosions during the assembly of galaxies provide magnetic seed fields – has been shown to reproduce the magnetic field in Milky Way-like galactic halos (Beck et al. 2013). The build up of the magnetic field at redshifts before z = 5 and the accordingly predicted rotation measure evolution are also in good agreement with current observations. Such magnetic fields present at high redshift are then transported out of the forming protogalaxies into the large-scale structure and pollute the ICM (in a similar fashion to metals transport). Here, complex velocity patterns, driven by the formation process of cosmic structures are further amplifying and distributing the magnetic fields. In galaxy clusters, the magnetic fields therefore get amplified to the observed μG level and produce the observed amplitude of rotation measures of several hundreds of rad/m2. We also demonstrate that heat conduction in such turbulent fields on average is equivalent to a suppression factor around 1/20th of the classical Spitzer value and in contrast to classical, isotropic heat transport leads to temperature structures within the ICM compatible with observations (Arth et al. 2014).

scholarly journals Near-infrared Polarimetry and Interstellar Magnetic Fields in the Galactic Center

2012 ◽  
Vol 10 (H16) ◽  
pp. 387-387
Author(s):  
S. Nishiyama ◽  
H. Hatano ◽  
T. Nagata ◽  
M. Tamura
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Near Infrared ◽  
Galactic Center ◽  
Smooth Transition ◽  
The Magnetic Field

AbstractWe present a large-scale view of the magnetic field (MF) in the central 3° × 2° region of our Galaxy. There is a smooth transition of the large-scale MF configuration in this region.

scholarly journals Probing interstellar magnetic fields with Supernova remnants

2008 ◽  
Vol 4 (S259) ◽  
pp. 75-80 ◽  
Author(s):  
Roland Kothes ◽  
Jo-Anne Brown
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Supernova Remnants ◽  
Large Scale ◽  
Galactic Plane ◽  
Field Configuration ◽  
Large Scale Magnetic Field ◽  
Rotation Measure ◽  
Field Lines ◽  
The Magnetic Field

AbstractAs Supernova remnants expand, their shock waves are freezing in and compressing the magnetic field lines they encounter; consequently we can use Supernova remnants as magnifying glasses for their ambient magnetic fields. We will describe a simple model to determine emission, polarization, and rotation measure characteristics of adiabatically expanding Supernova remnants and how we can exploit this model to gain information about the large scale magnetic field in our Galaxy. We will give two examples: The SNR DA530, which is located high above the Galactic plane, reveals information about the magnetic field in the halo of our Galaxy. The SNR G182.4+4.3 is located close to the anti-centre of our Galaxy and reveals the most probable direction where the large-scale magnetic field is perpendicular to the line of sight. This may help to decide on the large-scale magnetic field configuration of our Galaxy. But more observations of SNRs are needed.

scholarly journals Stability of H3O at extreme conditions and implications for the magnetic fields of Uranus and Neptune

2020 ◽  
Vol 117 (11) ◽  
pp. 5638-5643 ◽  
Author(s):  
Peihao Huang ◽  
Hanyu Liu ◽  
Jian Lv ◽  
Quan Li ◽  
Chunhong Long ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Thin Shell ◽  
Underlying Mechanism ◽  
Giant Planets ◽  
Dynamo Model ◽  
Extreme Conditions ◽  
Material Basis ◽  
The Magnetic Field ◽  
Planetary Dynamos

The anomalous nondipolar and nonaxisymmetric magnetic fields of Uranus and Neptune have long challenged conventional views of planetary dynamos. A thin-shell dynamo conjecture captures the observed phenomena but leaves unexplained the fundamental material basis and underlying mechanism. Here we report extensive quantum-mechanical calculations of polymorphism in the hydrogen–oxygen system at the pressures and temperatures of the deep interiors of these ice giant planets (to >600 GPa and 7,000 K). The results reveal the surprising stability of solid and fluid trihydrogen oxide (H3O) at these extreme conditions. Fluid H3O is metallic and calculated to be stable near the cores of Uranus and Neptune. As a convecting fluid, the material could give rise to the magnetic field consistent with the thin-shell dynamo model proposed for these planets. H3O could also be a major component in both solid and superionic forms in other (e.g., nonconvecting) layers. The results thus provide a materials basis for understanding the enigmatic magnetic-field anomalies and other aspects of the interiors of Uranus and Neptune. These findings have direct implications for the internal structure, composition, and dynamos of related exoplanets.

scholarly journals Generation of strong magnetic fields with a laser-driven coil

2018 ◽  
Vol 6 ◽  
Author(s):  
Zhe Zhang ◽  
Baojun Zhu ◽  
Yutong Li ◽  
Weiman Jiang ◽  
Dawei Yuan ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Experimental Studies ◽  
Diagnostic Techniques ◽  
Magnetic Field Generation ◽  
Field Generation ◽  
Research Fields ◽  
Laser Facility ◽  
Spatio Temporal ◽  
The Magnetic Field

As a promising new way to generate a controllable strong magnetic field, laser-driven magnetic coils have attracted interest in many research fields. In 2013, a kilotesla level magnetic field was achieved at the Gekko XII laser facility with a capacitor–coil target. A similar approach has been adopted in a number of laboratories, with a variety of targets of different shapes. The peak strength of the magnetic field varies from a few tesla to kilotesla, with different spatio-temporal ranges. The differences are determined by the target geometry and the parameters of the incident laser. Here we present a review of the results of recent experimental studies of laser-driven magnetic field generation, as well as a discussion of the diagnostic techniques required for such rapidly changing magnetic fields. As an extension of the magnetic field generation, some applications are discussed.

Solar Dynamo

2020 ◽  
Author(s):  
Robert Cameron
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Differential Rotation ◽  
Large Scale ◽  
Toroidal Field ◽  
Solar Dynamo ◽  
Small Scale ◽  
The Sun ◽  
The Magnetic Field

The solar dynamo is the action of flows inside the Sun to maintain its magnetic field against Ohmic decay. On small scales the magnetic field is seen at the solar surface as a ubiquitous “salt-and-pepper” disorganized field that may be generated directly by the turbulent convection. On large scales, the magnetic field is remarkably organized, with an 11-year activity cycle. During each cycle the field emerging in each hemisphere has a specific East–West alignment (known as Hale’s law) that alternates from cycle to cycle, and a statistical tendency for a North-South alignment (Joy’s law). The polar fields reverse sign during the period of maximum activity of each cycle. The relevant flows for the large-scale dynamo are those of convection, the bulk rotation of the Sun, and motions driven by magnetic fields, as well as flows produced by the interaction of these. Particularly important are the Sun’s large-scale differential rotation (for example, the equator rotates faster than the poles), and small-scale helical motions resulting from the Coriolis force acting on convective motions or on the motions associated with buoyantly rising magnetic flux. These two types of motions result in a magnetic cycle. In one phase of the cycle, differential rotation winds up a poloidal magnetic field to produce a toroidal field. Subsequently, helical motions are thought to bend the toroidal field to create new poloidal magnetic flux that reverses and replaces the poloidal field that was present at the start of the cycle. It is now clear that both small- and large-scale dynamo action are in principle possible, and the challenge is to understand which combination of flows and driving mechanisms are responsible for the time-dependent magnetic fields seen on the Sun.

Methanol masers and magnetic field in IRAS18089-1732

2017 ◽  
Vol 13 (S336) ◽  
pp. 285-286
Author(s):  
Daria Dall’Olio ◽  
W. H. T. Vlemmings ◽  
G. Surcis ◽  
H. Beuther ◽  
B. Lankhaar ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
High Mass ◽  
Small Scale ◽  
Star Forming ◽  
Large Scale Field ◽  
The Impact ◽  
Theoretical Simulations ◽  
The Magnetic Field

AbstractTheoretical simulations have shown that magnetic fields play an important role in massive star formation: they can suppress fragmentation in the star forming cloud, enhance accretion via disc and regulate outflows and jets. However, models require specific magnetic configurations and need more observational constraints to properly test the impact of magnetic fields. We investigate the magnetic field structure of the massive protostar IRAS18089-1732, analysing 6.7 GHz CH3OH maser MERLIN observations. IRAS18089-1732 is a well studied high mass protostar, showing a hot core chemistry, an accretion disc and a bipolar outflow. An ordered magnetic field oriented around its disc has been detected from previous observations of polarised dust. This gives us the chance to investigate how the magnetic field at the small scale probed by masers relates to the large scale field probed by the dust.

scholarly journals 3D model of magnetic fields evolution in dwarf irregular galaxies

2010 ◽  
Vol 6 (S274) ◽  
pp. 389-392
Author(s):  
Hubert Siejkowski ◽  
Marian Soida ◽  
Katarzyna Otmianowska-Mazur ◽  
Michał Hanasz ◽  
Dominik J. Bomans
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Gravitational Potential ◽  
Spiral Galaxies ◽  
Cosmic Ray ◽  
Dynamo Model ◽  
Slow Rotation ◽  
Irregular Galaxies ◽  
Dwarf Irregular Galaxies ◽  
The Magnetic Field

AbstractRadio observations show that magnetic fields are present in dwarf irregular galaxies (dIrr) and its strength is comparable to that found in spiral galaxies. Slow rotation, weak shear and shallow gravitational potential are the main features of a typical dIrr galaxy. These conditions of the interstellar medium in a dIrr galaxy seem to unfavourable for amplification of the magnetic field through the dynamo process. Cosmic-ray driven dynamo is one of the galactic dynamo model, which has been successfully tested in case of the spiral galaxies. We investigate this dynamo model in the ISM of a dIrr galaxy. We study its efficiency under the influence of slow rotation, weak shear and shallow gravitational potential. Additionally, the exploding supernovae are parametrised by the frequency of star formation and its modulation, to reproduce bursts and quiescent phases. We found that even slow galactic rotation with a low shearing rate amplifies the magnetic field, and that rapid rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.

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