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The consistency is awesome between over a dozen observations and the paradigm of radio lobes being immense sources of magnetic energy, flux, and relativistic electrons, – a magnetized universe.
The greater the total energy of an astrophysical phenomenon, the more restricted are the possible explanations. Magnetic energy is the most challenging because its origin is still considered problematic. We suggest that it is evident that the universe is magnetized because of radio lobes, ultra relativistic electrons, Faraday rotation measures, the polarized emission of extra galactic radio structures, the x-rays from relativistic electrons Comptonized on the CMB, and possibly extra galactic cosmic rays. The implied energies are so large that only the formation of supermassive black hole, (SMBH) at the center of every galaxy is remotely energetic enough to supply this immense energy, ~(1/10) 108M⊙c2 per galaxy. Only a galaxy cluster of 1000 galaxies has comparable energy, but it is inversely, (to the number of galaxies), rare per galaxy. Yet this energy appears to be shared between magnetic fields and accelerated relativistic particles, both electrons and ions. Only a large-scale coherent dynamo generating poloidal flux within the accretion disk forming the massive black hole makes a reasonable starting point. The subsequent winding of this dynamo-derived magnetic flux by conducting, angular momentum-dominated accreting matter, (~1011 turns near the event horizon in 108 years) produces the immense, coherent magnetic jets or total flux of radio lobes and similarly in star formation. By extending this same physics to supernova-neutron star formation, we predict that similar differential winding of the flux that couples explosion ejecta and a newly formed, rapidly rotating neutron star will produce similar phenomena of a magnetic jet and lobes in the forming supernova nebula. In all cases the conversion of force-free magnetic energy into accelerated ions and electrons is a major challenge.
Magnetic reconnection (Parker, 1957; Sweet, 1958; Petschek, 1964; Yamada et al., 2010; Biskamp, 2000; Tsuneta, 1996; Kivelson and Russell, 1995; Yamada, 2007; Birn et al., 2001; Drake et al., 2003) is considered important to many astrophysical phenomena including stellar flares, magnetospheric disruptions of magnetars, and dynamics of galactic lobes. Research on magnetic reconnection started with observations in solar coronae and in the Earths magnetosphere, and a classical theory was developed based on MHD. Recent progress has been made by understanding the two-fluid physics of reconnection, through space and astrophysical observations (Tsuneta, 1996; Kivelson and Russell, 1995), laboratory experiments (Yamada, 2007), and theory and numerical simulations (Birn et al., 2001; Daughton et al., 2006; Uzdensky and Kulsrud, 2006). Laboratory experiments dedicated to the study of the fundamental reconnection physics have tested the physics mechanisms and their required conditions, and have provided a much needed bridge between observations and theory. For example, the Magnetic Reconnection Experiment (MRX) experiment (http://mrx.pppl.gov) has rigorously cross-checked the leading theories though quantitative comparisons of the numerical simulations and space astrophysical observations (Mozer et al., 2002). Extensive data have been accumulated in a wide plasma parameter regime with Lundquist numbers of S = 100 − 3000, where S is a ratio of the magnetic diffusion time to the Alfven transit time.
A concise review of the past and ongoing laboratory experiments on rotating flows and the associated angular momentum transport relevant to astrophysical disks is given in three categories: hydrodynamic, magnetohydrodynamic, gas and plasma experiments. Future prospects for these experiments, especially for those directly relevant to the magnetorotational instability (MRI), are discussed with an emphasis on a newly proposed swirling gas and plasma experiment.
Collimated outflows (jets) are ubiquitous in the universe, appearing around sources as diverse as protostars and extragalactic supermassive black holes. Jets are thought to be magnetically collimated, and launched from a magnetized accretion disk surrounding a compact gravitating object. We have developed the first laboratory experiment to address time-dependent, episodic phenomena relevant to the poorly understood jet acceleration and collimation region (Ciardi et al., 2009). The experiments were performed on the MAGPIE pulsed power facility (1.5 MA, 250 ns) at Imperial College. The experimental results show the periodic ejections of magnetic bubbles naturally evolving into a heterogeneous jet propagating inside a channel made of self-collimated magnetic cavities. The results provide a unique view of the possible transition from a relatively steady-state jet launching to the observed highly structured outflows.
We have begun a series of laboratory experiments focused on understanding how coronal mass ejections (CME) interact and evolve in the solar wind. The experiments make use of the Helicon-Cathode (HelCat) plasma facility, and the Plasma Bubble eXperiment (PBeX). PBeX can generate CME-like structures (sphereomak geometry) that propagate into the high-density, magnetized background plasma of the HelCat device. The goal of the current research is to compare CME evolution under conditions where there is sheared flow in the background plasma, versus without flow; observations suggest that CME evolution is strongly influenced by such sheared flow regions. Results of these studies will be used to validate numerical simulations of CME evolution, in particular the 3D BATS-R-US MHD code of the University of Michigan. Initial studies have characterized the plasma bubble as it evolves into the background field with and without plasma (no shear).
In previous experiments by the authors a generation of intense field aligned current (FAC) system on Terrella poles was observed. In the present report a question of these currents origin in a low latitude boundary layer of magnetosphere is investigated. Experimental evidence of such a link was obtained by measurements of magnetic field generated by tangential sheared drag. Results suggest that compressional and Alfven waves are responsible for FAC generation. The study is most relevant to FAC generation in the Earth and Hermean magnetospheres following pressure jumps in Solar Wind.
At temperatures and densities that are typical of plasmas produced by lasers pulses interacting with solid targets, at power intensities I > 1012W/cm2, the classical Debye screening factor in nuclear reactions becomes comparable with the one of the solar core. Preliminary calculations about the total number of fusion reactions have been performed following an hydrodynamical approach for the description of the plasma dynamics. This approach is propaedeutic for future measurements of D-D fusion reaction rates.
Large regions of protoplanetary discs are believed to be too weakly ionised to support magnetorotational instabilities, because abundant tiny dust grains soak up free electrons and reduce the conductivity of the gas. At the outer edge of this “dead zone”, the ionisation fraction increases gradually and the resistivity drops until the magnetorotational instability can develop turbulence. We identify a new viscous instability which operates in the semi-turbulent transition region between “dead” and “alive” zones. The strength of the saturated turbulence depends strongly on the local resistivity in this transition region. A slight increase (decrease) in dust density leads to a slight increase (decrease) in resistivity and a slight decrease (increase) in turbulent viscosity. Such spatial variation in the turbulence strength causes a mass pile-up where the turbulence is weak, leading to a run-away process where turbulence is weakened and mass continues to pile up. The final result is the appearance of high-amplitude pressure bumps and deep pressure valleys. Here we present a local linear stability analysis of weakly ionised accretion discs and identify the linear instability responsible for the pressure bumps. A paper in preparation concerns numerical results which confirm and expand the existence of the linear instability.
The importance of reconnection in astrophysics has been widely recognized. It is instrumental in storing and releasing magnetic energy, the latter often in a dramatic fashion. A closely related process, playing in very low beta plasmas, is much less known. It is behind the acceleration of auroral particles in the low-density environment several 1000 km above the Earth. It involves the appearance of field-parallel voltages in presence of intense field-aligned currents. The underlying physical process is the release of magnetic shear stresses and conversion of the liberated magnetic energy into kinetic energy of the particles creating auroral arcs. In this process, field lines disconnect from the field anchored in the ionosphere and reconnect to other field lines. Because of the stiffness of the magnetic field, the process resembles mechanical fractures. It is typically active in the low-density magnetosphere of planets. However, it can also lead to significant energy conversion with high-energy particle production and subsequent gamma ray emissions in stellar magnetic fields, in particular of compact objects.
Our numerical simulations show that the reconnection of magnetic field becomes fast in the presence of weak turbulence in the way consistent with the Lazarian & Vishniac (1999) model of fast reconnection. This process in not only important for understanding of the origin and evolution of the large-scale magnetic field, but is seen as a possibly efficient particle accelerator producing cosmic rays through the first order Fermi process. In this work we study the properties of particle acceleration in the reconnection zones in our numerical simulations and show that the particles can be efficiently accelerated via the first order Fermi acceleration.
The theory of strong MHD turbulence with cross-helicity has been a subject of many recent studies. In this paper we focused our attention on low-imbalance limit and performed high-resolution 3D simulations. The results suggest that in this limit both w+=v+b and w−=v−b are cascaded strongly. The model for imbalance based on so-called “dynamic alignment” strongly contradicts numerical evidence.
Discovery of soft X-ray radiation from comet Hyakutake C/1996 B2 by space telescope ROSAT in March 1996 as well as establishing the regularity of the phenomenon for comets in general opened a new area of research for the plasma astrophysics. The first soft X-ray observations have been motivated by the results of a theoretical investigation on the efficiency of production of energetic photons, in the energy range 0.1-1 keV, by hot plasma clumps generated in dusty comets via high velocity collision with interplanetary dust at small heliocentric distances. Moreover, the soft X-ray luminosities measured significantly exceeded the value predicted. A short review of proposed theoretical models and mechanisms for explaining X-ray emission from comets as well as some prospects for the future X ray observations of comets are presented.
We apply large eddy simulation technique to carry out three-dimensional numerical simulation of compressible magnetohydrodynamic turbulence in conditions relevant local interstellar medium. According to large eddy simulation method, the large-scale part of the flow is computed directly and only small-scale structures of turbulence are modeled. The small-scale motion is eliminated from the initial system of equations of motion by filtering procedures and their effect is taken into account by special closures referred to as the subgrid-scale models. Establishment of weakly compressible limit with Kolmogorov-like density fluctuations spectrum is shown in present work. We use our computations results to study dynamics of the turbulent plasma beta and anisotropic properties of the magnetoplasma fluctuations in the local interstellar medium.
In the present investigation, radial diffusion of equatorially trapped electrons in the magnetospheres of Jupiter and Rotating Radio Transients (RRATs) are examined and compared. It is assumed that electrons lose energy through synchrotron radiation and the wave-particle interaction. The phase space density of the electrons, which go through gradB drift in Jupiter's and RRATs magnetospheres and thus resonate with the plasma waves, changes and this change predicted by the model seems to be consistent with the Pioneer 10 and Pioneer 11 data for Jupiter's case and a similar result obtained for RRATs.
We are developing a spherical hybrid model to study how the solar wind interacts with the solar system bodies. In this brief status report we introduce some lessons from the spherical grid development and illustrate the usage of the new model by showing a preliminary test run.
It is analytically shown that passages of comets near the Sun's surface with velocities more than 600 km/s is accompanied by aerodynamic crushing of their nuclei within the solar chromosphere and transversal expansion of the crushed matter. The deceleration of the flattened hypervelocity body within the solar photosphere has sharply impulsive and strongly explosive character. The specific energy release in the explosion zone near the solar surface 10-100 thousand times exceeds the evaporation heat of the nucleus material, so that the process is accompanied by generation of high-temperature plasma and non-stationary explosive phenomena around the photosphere. Spectral observations of these phenomena by SOHO and SDO type space observatories with high spatial and temporal resolutions are of interest for the plasma astrophysics as well as the physics of solar flares.
The Solar System formation PFO–CFO hypothesis is developed in the direction of creation of a phenomenological model focused on solution of a number of paradoxes and answering to a number of mysterious questions under the same cover. For explanation of the events and processes that occurred over the period from the middle ages of the pre-solar star to the Solar System formation, original approaches are applied.
One of the challenges in constructing global magnetohydrodynamic (MHD) models of the inner heliosphere for, e.g., space weather forecasting purposes, is to correctly capture the acceleration and expansion of the solar wind. In many current models, the solar wind is driven by varying the polytropic index so that a desired heating is obtained. While such schemes can yield solar wind properties consistent with observations, they are not problem-free. In this work, we demonstrate by performing MHD simulations that altering the polytropic index affects the properties of propagating shocks significantly, which in turn affect the predicted space weather conditions. Thus, driving the solar wind with such a mechanism should be used with care in simulations where correctly capturing the shock physics is essential. As a remedy, we present a simple heating function formulation by which the polytropic wind can be used while still modeling the shock physics correctly.
Anomalous momentum transport in a typical astrophysical return-current beam plasma system is studied by means of two-dimensional PIC code simulations. A forward going hot electron beam compensated by a cold return beam is considered. A linear dispersion analysis predicts the linerarly unstable wave modes. Our simulation reveals that the nonlinerly generated waves and the consequent wave-particle interactions cause the electron heating and the relaxation of the electron drifts. Both, the developments of electrostatic and electromagnetic waves are analyzed as well as the roles they play in energy conversion. In particular it is found that the relaxation of electron drifts is stronger if the electromagnetic turbulence is taken into account.
It is shown that the magnetic current-driven (‘kink-type’) instability produces flow and field patterns with helicity and even with α-effect but only if the magnetic background field possesses non-vanishing current helicity B⋅ curl B by itself. Fields with positive large-scale current helicity lead to negative small-scale kinetic helicity. The resulting α-effect is positive. These results are very strict for cylindric setups without z-dependence of the background fields. The sign rules also hold for the more complicated cases in spheres where the toroidal fields are the result of the action of differential rotation (induced from fossil poloidal fields) at least for the case that the global rotation is switched off after the onset of the instability.