|The usual definition of
what a galaxy is: 'An island universe', or 'A vast collection of
stars' is not wrong, but it is misleading. Because of the
vast distances that separate stars even in the most densely
packed regions of most galaxies, a better definition is: 'A vast
formation of plasma clouds that contain electrical currents and
occasional, widely distributed tiny lumped points of matter
called nebulae, stars and planets.'
The shape that characterizes most galaxies was first described by Hannes Alfven in 1981.
The shape he proposed is shown here. This diagram is a vertical cross section of a three dimensional figure. The horizontal line at the center of the diagram is actually a circular disk lying in the horizontal plane. It is this disk, when viewed not from the edge as it is here, but more face on, that is the familiar spiral shape picture of a galaxy that we are used to seeing. The parallel vertical lines coming out from the center of the galaxy (along its axis of rotation) represent a strong electrical current in a plasma that sometimes is visible as a "jet".
The two pairs of letters - DL - in the sketch are Double Layers within the jet plasma. Recall that DLs contain strong E-fields and are the source of radio frequency emissions. The two amorphous shapes at the left of the diagram show the resulting typical "double radio source" that is observed in many galaxies. These are due to the presence of DLs. In some galaxies the jet plasma is in the dark current mode; in others it is clearly visible.
This is Centaurus A. The jet is clearly visible in this image. Halton Arp's contention that quasars are emitted from the centers of Seyfert galaxies along their 'secondary axes' (axes of rotation) is supported by these pictures. Recall that DLs are also the locations of strong electromagnetic z-pinches which can compress dispersed material into denser objects.
The general shape of a
rotating disk carrying electrical currents in the shape shown
by Alfven defines what is called the homopolar motor -
generator. Note that the horizontal disk (the arms of
the galaxy) is where the current, I, is least spread
out - the current density is greatest. This is where
Population I stars are usually found.
In many galaxies the jet structure cannot be seen in visible light. So until the development of infrared and x-ray orbiting satellite telescopes, most of these features remained undiscovered. There are now many images of galaxies that show the Alfven structure. The image below was taken by the Subaru
orbiting IR telescope of galaxy M 82.
Even our neighboring Andromeda galaxy, M 31, shows the disk like structure of the homopolar motor-generator morphology. Below on the right is a normal, visible light photograph of M 31. Below on the left is an image of that same object obtained by the Infrared Space Observatory (ISO) operated by ESA.
|But Alfven also proposed
that individual stars themselves had similar morphologies. He
proposed an almost identical diagram for the operation of a
typical star. Once again the plasmas involved may or may not all
be in one of the visible modes of operation. So not all images
of stars show this structure - but many do. Alfven's
heliospheric circuit is shown below on the left. Because
our Sun is a typical star, this diagram would apply equally well
This proposal remained
in the realm of conjecture until the spring of the year 2001
when the spacecraft Ulysses discovered long plasma 'tubes'
emanating from the bottom pole of our Sun. These tubes are
long enough to extend out farther than the distance of the
orbit of Mars from the Sun. There are also many images
available now of individual 'jetted stars'. Of course, Alfven
believed all stars were jetted - but some less visibly than
|Notice in the right hand
image above (Goddard Space Flight Center) that the
'planets' (Herbig-Haro objects) are formed in a collinear array
along the jet axis of the parent star. These clumpings are
probably formed by DLs at those locations. In the center image
(above) the tell-tale twisting shape of a large Birkeland
current containing DLs is clearly visible.
Whether we choose to call it the homopolar motor - generator, the jetted disk, or the Alfven circuit, this shape is being seen with increasing frequency as more accurate and broader bandwidth instruments are developed. (Notice, for example, the shape of the "Crab pulsar" shown on the Main page of this site.) All the images shown below are of stars. All exhibit the homopolar disk shape.
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