This subject of currents and circuits and wiring in a cosmic setting is very important to us here, I venture to say. If we posit that plasma is a conducting medium with small but finite resistance, so that it is neither a superconductor nor do its accompanying magnetic field lines get "frozen in" as theory might allow, then physically what is possibly happening?
As a
caveat emptor, let me advise readers that this is a pretty imaginative exercise. One does not normally "see" an electric current in visible light, although visible light is sometimes emitted by phenomena caused by a current of charged particles, such as lightning, or synchrotron radiation. —and the radiation is not always in the visible wavelengths to us, but may be to our instruments, and so can be shifted mathematically to representative "false" (but visible) colors so we can bring our pretty clever eyes and brain to bear on the identification. Currents are accompanied by something else, too: magnetic fields. "Fields" are also not visible, but that doesn't mean that they are undetectable, either.
We can view visible images of the magnetic field(s) on the Sun's disk at
http://sohowww.nascom.nasa.gov/data/rea ... mages.html obtained with an instrument called an imaging vector magnetograph. Current flows (on the Sun's disk) can be inferred from the magnetic field values (polarization and intensity from the measured amount of splitting of what are called Zeeman lines) by calculating the 'curl' of the magnetic field and applying Maxwell's equations, according to the web site for the University of Hawaii's astronomy department.
Magnetic fields are also able to be measured and mapped on a galactic scale through the same general approach, using radio telescopes.
http://www.mpifr-bonn.mpg.de/staff/wshe ... ssier.html If you'll take the leap with me, identifying where and how strong the magnetic fields along the arms and elsewhere around a galaxy lets you infer where the electric currents are that cause those fields. If electrons are moving relative to an observer, as has been discussed on this Forum in the recent past, they A) constitute what is called a current, and B) always have an accompanying magnetic field. Non-moving electric charges, such as may be stored in a battery or in a capacitor, don't exhibit a magnetic field.
Dave Talbott is spot on in saying that it is not (necessarily) charged particles in a current moving near the speed of light that constitute the current; it is their drift velocity which constitutes a current. The more, say, electrons drifting along through a given cross-section or area during a (standardized) 1 second period, the more "current" you have flowing. Current, measured in amperes, is basically charges per second through an area which is
fixed relative to the observer.
If one thought that the "wires" or cables in space were just gas particles bouncing around, it seems clear that they would tend to expand and dissipate and to try to get their "pressure" to match that of the surrounding "empty space". Pop a balloon in space and where would the gas atoms or molecules go? Away! They wouldn't line up into a narrow tube or filament and start conducting electricity! Gravity doesn't make them do something like that, even if we assume it is acting on them.
If you have a volume of low density,
ionized material in space, possibly ionized by, say ultraviolet light from a nearby star, particularly if it is in a region in which a magnetic field may exist, its state is that of plasma. Plasma will tend to distribute itself and subdivide itself into regions of (slightly) different net charge, separated by double layers which tend to act as insulators, and diode-like, prevent the passage of low-energy charged particles from one area into an adjacent one. Charge separation begets electric fields, so now forces start to be exerted on charged particles simply from the self-separating rules of plasma physics. A fluorescent light does this same thing in your garage or office.
Plasma will subsequently tend to change from a tenuous volume into separated sheets, and those in turn will start to pinch themselves into filamentary shapes which are generally long and twisty, sometimes feathery and sometimes branching and angular. Watch a plasma ball at work, and this is clearly demonstrated. The electrons being forced, by the large voltage differential, into the low pressure gas in the ball excite and heat it to a plasma state, and then plasma physics takes over and the plasma pinches itself into glowing filaments which conduct the electrons from the center to the more positively charged outer glass globe.
Electric currents in an evacuated space
form their own long, thin shapes. There may be many intertwined plasma filaments oriented in the same direction, twisting and wrapping around each other in pairs (Biot-Savart attraction) while being separated by their double layers and the repulsive force from electrostatic repulsion when they get "too close" together, and repulsion overcomes attraction. They are like nerves conducting electric impulses, made up of innumerable neurons, each carrying part of the signal along the pathway. The EU model says that it is these Birkeland currents which operate like cross-country power cables, accompanied by the same sorts of magnetic fields that accompany high-tension lines. and transporting the electric currents which power and sustain the stars and galaxies.
It is the Birkeland currents which feed electric power into the ionosphere and power the auroras, and bring electric power into the planet itself, and jet it back out to space around the poles to rejoin the solar plasma filling the heliosphere. It is Birkeland currents generated at the Sun's surface that help eject billions of tons of plasma away from the solar surface and gravity, out into space as coronal mass ejections (CMEs). It is likely Birkeland currents on a rather grand scale which move through space, creating stars at intervals and weaving together galactic forms in the process. We circle our stars, separated by silent lightyears of distance, all held tightly in the warp and weft of the currents in space.
Not to put too fine a point on it, it should be able to be described by plasma physics and by observing and documenting what plasmas do on and near our planets and our Sun. It's just that it's not that easy.
Jim
