Pink Noise - Leonid Korogodski [52]
As plasma physics tells us, double layers form in narrow cross-sections along the filaments. This is where most of the voltage is squeezed into. More voltage means higher resistance. Therefore, matter accumulates within the double layers, where the galactic disks eventually form, like beads along a string.
Three major forces act on Birkeland filaments:
The 1/r attractive electromagnetic force.
The electric current in each filament creates a magnetic field that exerts force on the other filament. Parallel electric currents of the same direction attract, while those of the opposite direction repel. In our case, this force is attractive and proportional to the product of current in the filaments. It depends on the distance r between them as 1/r, if the filaments’ lengths are much greater than r. This is because the current is the same along the entire length of each filament. This force is often called the Biot–Savart force.
Top: The spiral galaxy M81. NASA / JPL–Caltech / S. Willner, Harvard–Smithsonian Center for Astrophysics. Bottom: Galaxy formation stages from a simulation run by Anthony L. Peratt, Los Alamos National Laboratory. Copyright © 1986 Institute of Electrical and Electronics Engineers.
The 1/r2 force of gravity.
This force is proportional to the product of mass in the filaments. If plasma density were uniform along the filaments, this force would also have been 1/r. But matter accumulates only in the relatively narrow cross-sections where double layers form. Elsewhere, mass is negligible, and therefore the force of gravity between the filaments is 1/r2.
The 1/r4 repulsive electromagnetic force.
Positively charged and negatively charged particles spiral around the magnetic field lines in opposite directions. This adds a circular (properly called azimuthal) component to the total electric current in the filaments. Azimuthal currents of the same orientation repel; of the opposite, attract. In our case, they repel. The cumulative force is proportional to the product of magnetic momenta of the filaments and behaves as 1/r4. Importantly, the interaction of these azimuthal currents also produces a torque that eventually makes the filaments turn around each other, like a hurricane.
Because it’s 1/r, the attractive electromagnetic force is dominant at the long range, but the 1/r4 repulsive force overtakes it at the close range. Simulations show that gravity does not make much impact at the galactic scale.
Because the attractive force is 1/r, the plasma filaments usually form pairs, occasionally triples. The number of filaments determines the number of spiral arms to form. But one-armed galaxies are possible as well, if one of the filaments is too weak to produce stars.
Double radio galaxy is the first stage. The cross-sections of each filament emit the so-called synchrotron radiation in the radio range, a kind of electromagnetic radiation with a specific, recognizable spectrum, which can only be produced by relativistic electrons accelerating in an electric field.
QUASAR: a quasi-stellar radio source. Usually thought to be extremely far away, they may be actually much closer to us.
As the filaments are drawn toward each other, the plasma in the center is squeezed by the converging magnetic mirrors, producing a plasmoid that behaves like a quasar.
Eventually, the plasma in the center is compressed so much that stars begin to form in the elliptical sump, where the magnetic field is lower.
By this time, the short-range repulsive force is already felt, and the filaments begin to turn around each other, trailing plasma in the spiral arms, along which electric currents start to flow.
A portion of the plasma filament connecting the galaxies NGC 1409 (right) and NGC 1410 (left) may have captured some dust and therefore turned visible. NASA / William C. Keel, University of Alabama.
The electromagnetic pinch in those currents compresses plasma such that, reaching a certain threshold, stars begin to form throughout the entire spiral arm at