In the previous episode, we investigated Peratt’s concept of the evolution of cosmic
plasma from a filamentary state to the development of double radio and quasars.
The time frame of this study was based upon the scaling of the simulation parameters
to galactic dimensions and would span some 10^8 to 10^9 years. We will now examine what
might happen over the next 1-5 x 10^9 years. Let’s dive in and find out more
Gross Radio Properties of Galaxies
The radio power of galaxies ranges from about 10^30 to about 10^38 Watts, and relative to
their optical luminosity from less than 10^-6 to about 1. The distribution in power is described by
means of the radio luminosity function RLF., which represents the number of radio-emitting galaxies
per unit volume as a function of the monochromatic power at a certain frequency.
The radio luminosity function suggests a continuity in the morphological types
of radio-emitting galaxies. Above 10^26 the main contribution comes
from quasars and classical double radio galaxies. In the region 10^23 to 10^26 the
ellipticals galaxies dominate, while below 10^23 the power comes principally from spiral galaxies.
In the region 10^21 and 10^23, an overlap of prial and elliptical galaxies occurs.
The ellipticals are in fact a hybrid class, containing bona fide ellipticals
along with N galaxies which have a bright nucleus surrounded by a faint nebulosity,
to that of cD galaxies which are giant ellipticals with very extended radiohalos.
Apart from the radical change in morphology between elliptical
and spiral, the spiral galaxies have not only a compact nuclear component of size
0.1 to 1 kpc but also a component of size 10kpc coincident with the spiral disk.
Overlapping the powerful radio ellipticals having Seyfert-like nuclear spectra and the spiral
galaxies are the Seyfert spirals themselves, comprising 1 percent of all spiral types.
In contrast to the ellipticals, spiral galaxies rarely have compact nuclear sources
and are rarely associated with extended radio lobes.
This table shows the properties of galactic radio sources with decreasing redshift.
In this diagram, we can see the positions of radio sources, both extended and compact
on a linear-size radio luminosity plot. The bulk of the classical double radio
galaxies possessing an elliptical galaxy have a spatial extent between a few tens of kiloparsecs
to many hundreds of kiloparsecs. The radio quasars appear in two distinct populations;
extended sources with dimensions of several kiloparsecs to several hundreds of kiloparsecs
and compact sources 2-8 parsecs. Most of the spiral galaxies are found to be clustered
according to a size of 10 - 80 kparsecs and have much lower luminosities.
Finally, unlike the other properties, the radio spectra of the spiral galaxies
are similar to those of the radio galaxies.
Let’s now examine the transition of two interacting Birkeland currents
of galactic dimensions into the morphology of a spiral galaxy.
It is important to note that these images convey the overall changes to the shape
but do not convey the dynamics of the plasma within the bulk forms.
These images show cross-sectional views of two plasma filaments
of width 35 kpc and separation of 80kpc.
For the case of a field-aligned electric field oriented along the +z direction,
so out of the screen, the electrons in both columns spiral downwards
in a counterclockwise rotation. Likewise, the ions spiral upwards in a clockwise rotation.
For the initial separation depicted the force between the filaments is predominately
attractive and the relative velocity of the two plasma filaments are approximately 1000km/s.
The relative velocity of the plasma increases directly with increasing current and reaches
a velocity of several thousand km per second near minimum separation.
The translational momentum is converted into angular momentum due to the torque between the
filaments. This causes a reconfiguration of the current/plasma cross-sectional profiles
in the filaments. The initial circular cross-sections are deformed into oval shapes
that then take on a jelly bean-like profile prior to forming embryonic spiral arms.
During this process, the elliptically shaped quasar formed midway between the
two synchrotron radiating plasmas is enclosed by the plasmas themselves as they spiral inwards.
During this time the quasar dimensions narrow
and the enclosed sump density increases because of the increasing isobaric pressure.
The 50kpc channel is reduced to a few kpc lengths. The trailing spiral arms then lengthen with time.
Bostick was the first to record the formation of spiral structures in the laboratory
from interacting plasmoids and to note the striking similarity to their galactic analogs.
So starting at the beginning we first see the condensation of current-carrying plasma
into the two pinching filaments. Then the formation of an elliptical sump midway
between filaments with subsequent capture and compression of intergalactic plasma
and then a burst of synchrotron radiation from each filament.
These steps take us firstly from a Double Radio Galaxy to a radio quasar. As the radio lobes
continue to decrease while at the same time the central component becomes more active.
The increased compression of the plasma in the elliptical sump
intensifies the synchrotron radiation from the compact component.
The compact component can appear as an isolated synchrotron source during this period.
We noe enter a transitional period which invoices the formation of several peculiar
plasma geometries. During this period the incoming plasma of the extended components
has not yet coalesced with the quasar centre. The synchrotron radio activity in the extended
components has decreased markedly and the quasar core consists of highly activated,
strongly radiating, dense plasma because of the continued magnetic sump compression.
The density decreased with the isobaric gradient.
The inward velocities of the isobars are not linear but tend to pulsate as they compress.
These steps take us from the radio-quiet quasi-stellar object to a Seyfert spiral.
As we continue the coalesce of the outer plasma component onto the excited compact centre begins.
Additionally, the continued electromagnetic compression on plasma confined in the sump can
be expected to start the gravitational collapse of this material. This manifests two effects:
the disappearance of the quasar plasma emission and the appearance of stars.
The simulations show that Radio Galaxy form, followed by more quasars. This then leads to
the formation of elliptical galaxies. Then as the synchrotron radiating Birkeland current-conducting
outer plasma components move inwards on the elliptical core, peculiar galaxies form and in
sequence the spiral types Sd, Sc and then Sa form, or their barred equivalents. Stars form first in
the densely compressed elliptical core and then in the pinches plasma that make up the spiral arms.
Multiple Interacting Galaxies
Birkeland current often occur in sheets and where these have dimensions of a hundred kiloparsecs or
more, filamentation of the plasma into a number of galaxies can take place. These
filaments will have a tendency to pair up. This can lead to a close grouping of spiral galaxies.
The classification of multiple interacting galaxies
can be spiral-spiral or spiral-peculiar but do not include elliptical or lenticular galaxies.
Moreover, these spirals tend to be Seyfert spirals or their barred equivalent.
Here is an example of a simulation run with a single plasma sheet forming adjacent galaxies.
The connection of a spiral configuration to a spherical or oval configuration by a thin
filament is a commonly observed morphology, both in simulations and in laboratory experiments.
A galactic example of this is Markarian 205 and NGC4319. Here are some other examples.
Because the Birkeland current is part of a closed-circuit element,
galaxies occur periodically along the gigaparsec to sub gigaparsec filament
where double layers form and where interactions with neighbouring filaments occur.
The Centaurus chain of galaxies may be an example of galaxies forming along filaments.
The Chemical Composition of Forming Galaxies
Cosmic plasma generally is composed of elements in varying abundance. Under the influence of the
E x B force, both electrons and ions drift with the velocity so that the plasma as a whole moves
radially inwards. This mechanism provides a very efficient convection process for the
accumulation of matter from plasma. The material should form as a filamentary structure about the
twisted magnetic flux tubes, the lines of which are commonly referred to as ‘magnetic ropes’.
Magnetic ropes should tend to coincide with material filaments that have a higher density
than the surroundings. The cosmic magnetic flux tubes are not directly observable, but
the associated filaments of condensed matter can be observed by the radiation they emit and absorb.
Marklund found a stationary state when the inward convection of ions and electrons towards the axis
of a filament was matched by recombination and outward diffusion of the neutralised plasma.
The equilibrium density of the ionised component normally has a maximum at the axis.
Due to these mechanisms, hollow cylinders of matter will form about the flux tubes.
Due to the radiated loss of energy, the filaments cool and a temperature gradient is associated with
plasma. As the radial transport depends on the ionisation potential of the element, elements
with the lowest ionisation potentials are brought closest to the axis. The most abundant elements
of cosmical plasma can be divided into groups of roughly equal ionisation potentials as follows:
He - 24eV, H, O, N 13 eV
C, S 11 eV Fe, Si, Mg 8eV
These elements can be expected to form hollow cylinders whose radii increase with
the ionisation potential. Helium will make up the most widely distributed outer layer;
hydrogen, oxygen and nitrogen should form the middle layers; and iron, silicon and magnesium
will make up the inner layers. Overlap between the layers can be expected and for the case of
galaxies, the metal to hydrogen ratio should be maximum near the centre and decrease outwards.
In the case of a fully ionised hydrogenic plasma, like the one used in the simulation, the ions
drift inwards until they reach a radius where the temperature is well below the ionisation potential
and the rate of recombination of the hydrogen plasma is considerable.
Because of this ion pump-action, hydrogenic plasma will evacuate from the surroundings
and neutral hydrogen will be most heavily deposited in regions of strong magnetic flux.
High-resolution observations of neutral hydrogen
in irregular and spiral galaxies usually reveal very extended H1 distributions. Contour maps
of the H1 typically show a relative lack of H1 in the cores of spiral galaxies
but high h1 content in the surrounding region, usually in the shape of a ‘horse
shoe’ This region is not uniform but may have two or more peaks in neutral hydrogen content.
Considering the power source of the Galactic Birkeland currents
Where we consider two Birkeland currents attracting each other
a problem arises whereby there is a necessity to account for the complete electrical circuits
in which the current flows. The discussion of the entire circuit is far more speculative
than the aspects we have discussed so far and this was not modelled in
Peratt’s simulation. Nevertheless based upon the properties of plasma in the laboratory,
a reasonable guess about the properties of the cosmic circuit is possible.
In its simplest form, an electrical circuit consists of a voltage source, a load,
and the transmission line between the source and the load. In this example, the transmission line
and the load are the field-aligned currents that are likely to form a series of double layers.
Like most field-aligned currents in cosmical plasma,
the currents flowing from the source to the double layer are likely to be pinched.
This means they consist of filaments. The magnetic field is given by the following equation:
Where r is the radius of the filament or bunch of filaments.
In circuit theory, the magnetic energy of
the circuit is described as being due to an inductance L
Where I is the current. The integral should be taken over
the whole region where I produces a magnetic field.
Since the circuit conducts filamentary currents, the circuit consists of a resistance,
an inductance, and an electrostatic double-layer formed along the filaments,
all fed by an EMF. The circuit equation looks like this…
If the resistance R is negligible as is often the case in cosmic situations, the current grows as
long as the voltage of the source is greater than the sum of the potentials over the double layers.
For Peratt’s simulation 1/2LI^2 is 2.5 x 10^53J
I = 2.15 x 10^19 A So that L = 1.08 x 10^15 H
The rate of increase of the current is 3.89 x 10^5 A/s.
For these values, Ldi/dt = 4.2 x 10^20V
In analogy to the rotating magnetised plasma dynamo’s that drive cosmic Birkeland currents
of lesser dimensions, a magnetised plasma with a size of the order of the largest objects observed
in the universe, 10-50Mpv, moving through 10^9T field lines at 1000 km/s. Will produce an EMF
of the order of 10^20V. Using Cygnus A dimensioned current cross-sections at 35kpc, and the knowledge
that the width/length ratio of laboratory filaments is generally in a range 10^-3 to 10^-5,
a typical filament length associated with the dynamo source may be of the order of 350Mpc.
If the voltage of the source suddenly becomes zero, the current will continue to flow
but will decrease with the time constant Tc = LI/deltaV which is approximately 10^14 seconds.
Summary
Current Astronomy has difficulty in explaining the dynamics of elliptical and spiral galaxies in the
absence of magnetic fields and plasma physics. In a very perceptive paper, Toomre questions the
dilemma that photographic data of galactic mergers present to gravitational N body simulations.
The complexity of this problem is further compounded by the existence of peculiar galaxies,
the morphologies and topologies of which do not inspire confidence
in theories postulating linear waves or shocks as the moulding forces.
So does Peratt’s paper offer a different insight into how galaxies might form?
I think this is a great step in the right direction and certainly matches
a lot of the observation evidence of different types of galaxies.
This does also present some interesting questions about what ‘powers’ a galaxy,
what does it mean for Alfven galactic circuit model? What lies at the heart of a galaxy then?
What does it mean for Lerner’s plasmoid model? Could this concept also apply to smaller filaments
like star filaments? These are all questions that I would like to address in the next part.