2a2. Galactic Filaments (Peratt)
© Lloyd

by A.L. Peratt
_1. Introduction
_2. Filamentation by Birkeland Currents
_3. Field Aligned Electric Fields
_4. Galactic Dimentioned Birkeland Currents
_5. The Large Scale Structure of the Plasma Universe
_6. Confining and Interacting Forces Between Cosmic Currents
_7. Synchrotron Emission from Pinched Particle Beams
_8. Conclusions
_In plasma, electromagnetic forces exceed gravitational forces by a factor of 10^36, and electromagnetism is ~10^7 times stronger than gravity even in neutral hydrogen regions, where the degree of ionization is a miniscule 10^-4.
_The observational evidence for galactic-dimensioned Birkeland currents is given based on the direct comparison of the synchrotron radiation properties of simulated currents to those of extra-galactic sources including quasars and double radio galaxies.
_1. Introduction
_The universe is 99.999% matter in the plasma state.
_For the most part, plasma consists of particles at high temperature, i.e., an energetic state.
_And like all energetic plasma, the volume of plasma is inhomogeneous and consists of plasmas with differing temperatures, magnetization, degree of ionization, chemical constituency, and relative motion.
_It is this latter property, often the result of the first four properties, that produces filamentation.
_Plasmas in relative motion are coupled by the currents they drive in each other.
_Any imbalance in the constitutive properties of a plasma can set it in motion (if, in fact, it has not already derived from an evolving, motional state).
_The moving plasma, i.e., charged particle flows, are currents that produce self magnetic fields, however weak.
_The motion of any other plasma across weak magnetic fields produces and amplifies electromagnetic forces, the energy of which can be transported over large distances via currents that tend to flow along magnetic lines of force.
_These "field-aligned currents", called Birkeland currents in planetary magnetospheres, should also exist in cosmic plasma.
_The dissipation of the source energy from evolving or moving plasma in localized regions can then lead to pinches and condense states.
_Where double layers form in the pinches, strong electric fields can accelerate the charged particles to high energies, including gamma ray energies.
_These should then display the characteristics of relativistic charged particle beams in laboratory surroundings, for example, the production of microwaves, synchrotron radiation, and non-linear behavior such as periodicities and "flickering".
_2. Filamentation by Birkeland Currents
_An electromotive force [v x B dl giving rise to electrical currents in conducting media is produced wherever a relative perpendicular motion of plasma and magnetic fields exist.
_An example of this is ... aurora dynamics, now attributed to filamentation of Birkeland charged-particle sheets following the earth's dipole magnetic-field lines into vortex current bundles.
_3. Field Aligned Electric Fields
_Magnetic field-aligned electric fields ... can have important consequences in cosmic plasma, including the "unfreezing" magnetic fields, the acceleration of electrons to very high energies, and filamentation of the plasma itself.
_In magnetized nonhomogeneous astrophysical plasma, a number of mechanisms are present that can generate field-aligned electric fields.
_These include anomolous resistivity caused by wave-particle interations, magnetic mirror effects involving trapped particles in magnetic-field gradients, and electric double layers due to localized charge separation.
_It is the last mechanism that has been found to be remarkably prolific in producing appreciable potential drops in neutral plasma.
_Moreover, Birkeland currents and double layers appear to be associated phenomena, and both laboratory experiments and computer simulations have shown the formation of a series of double layers along current-carrying plasma filaments or beams.
_When double layers (or a series of double layers) form in adjacent Birkeland current filaments, field-aligned electric fields are generated, which then serve to accelerate electrons and ions within the regions.
_4. Galactic Dimentioned Birkeland Currents
_Extrapolating the size and strength of magnteospheric currents to interstellar space leads to the suggestion that confined current flows in interstellar coulds assists in their formation.
_The existence of galactic dimensioned Birkeland filaments was hypothesized.
_A galactic magnetic field of the order B.G = 10^-9 to 10^-10T associated with a galactic dimension of 10^20 to 10^21m suggests the galactic current be of the order I.G = 10^17 to 10^19A.
_In the galactic dimensioned Birkeland current model, the width of a typical filament may be taken to be 35 kpc (~10^21m), separated from neighboring filaments by a similar distance.
_Since current filaments in laboratory plasmas generally have a width/length ratio in the range 10^-3 to 10^-5, a typical 35 kpc wide filament may have an overall length between 35 Mpc and 3.5 Gpc with an average length of 350 Mpc.
_The circuit, of course, is closed over this distance.
_5. The Large Scale Structure of the Plasma Universe
_Surface currents, delineating plasma regions of different magnetization, temperature, density, and chemical composition give space a cellular structure.
_As current-carrying sheet beams collect into filaments, the morphology of the surface currents is filamentary.
_For the case of tenuous cosmic plasmas, the thermokinetic pressure is often negligible and hence the magnetic field is force-free.
_Under the influence of the electromagnetic fields the charged particles drift with the velocity v = (E x B)/"E"^2 (1).
_The overall plasma flow is inwards and matter is accumulated in the filaments which, because of their qualitative field line pattern, are called magnetic ropes.
_Magnetic ropes should therefore tend to coincide with material filaments that have a higher density than the surroundings.
_The cosmic magnetic ropes (current filaments) are not observable themselves, but the associated filaments of condensed matter can be observed by the radiation they emit and absorb.
_It is because of the convection and neutralization of plasma into radiatively cooled current filaments (due to synchrotron losses) that matter in the plasma universe should often display a filamentary morphology (Fig. 1).
_6. Confining and Interacting Forces Between Cosmic Currents
_In contrast to the gravitational and electromagnetic forces that determine the characteristic of an individual beam (in the Carlqvist Relation), interactions between beams are always dominated by electromagnetic Biot-Savart forces.
_The Biot-Savart force is F.21 = [j.2 x B.21 d^3 r (3), for all space, where j.2 x B.21 is the Lorentz force between the field B.21 induced by a current I.1 on the current density j.2 at current I.2.
_Parallel axial currents within the filaments are long-range attractive, while circular (helical) currents within the filaments (as the electrons gyrate along the axial magnetic field) are short-range repulsive.
_If the axial currents are able to bring the filaments close enough together so that the repulsive component of the Lorentz force becomes important, the circular currents repulse and brake, and release energy in the form of synchrotron radiation.
_Fig. 2 illustrates the cross-sections of the filaments over a 10^9 yr period.
_7. Synchrotron Emission from Pinched Particle Beams
_One of the most important processes that limit the energies attainable in particle accelerators is the radiative loss by electrons accelerated by the magnetic field of a betatron or synchrotron.
_Synchrotron radiation is characterized by: a generation of frequencies appreciably higher than the cyclotron frequency of the electrons; continuous spectra ...; increasing beam directivity with increasing relativistic factor (see formula); and polarized electromagnetic wave vectors.
_Z-pinches are among the most prolific radiators of synchrotron radiation known.
_The radiation produced from the plasma configuration shown in the second frame of Fig. 2 replicates both the isophotal and power spectra from double radio galaxies (Fig. 3).
_Because the highly relativistic electrons depicted in Fig. 2 flow in direction outwards from the plane of the figure, the synchrotron radiation is also beamed in this direction.
_The monochromatic power of quasars and double radio galaxies span a range of about 10^33W to 10^39W.
_(Cygnus A has an estimated radio luminosity of 1.6 to 4.4 x 10^37W.)
_The left column of Fig. 3 suggests that previously apparently unrelated double radio galaxies all belong to the same species but are simply seen at different times in their evolution.
_8. Conclusions
_The importance of applying electromagnetism and plasma physics to the problem of radio galaxy, galaxy and star formation derives from the fact that the universe is largely matter in its plasma state, i.e., a universe of plasma.
_The motion of this plasma in local regions can lead to pinches and ultimately condense states of matter.
_Where double layers form, strong electric fields can accelerate particles to high energies.
_The intensity and patterns of synchrotron radiation observed in the model simulations are in excellent agreement with those observed from double radio galaxies.
_[See Fig. 3.]


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