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Mainstream astronomers’ reliance on gravity as the primal force shaping the
Universe, has restricted them to thinking in terms of spherical explosions and
voids or bubbles, created by dying stars. Around these supposed voids, gas
filaments can be seen arcing away. Our Sun sits in the middle of an enormous
void called the ‘local bubble’. They say this contains million-degree
ionized hydrogen gas surrounded by a wall of colder, denser neutral gas.
Within this hot bubble, gas density is much sparser. At first they thought that the local
bubble was an asymmetric cavity of 330 to 490 light years in diameter. This
implied that two bubbles might have collided and merged. The most important point to note is that
they believe the local bubble is deficient in neutral gas. In all the literature they keep
describing it as ‘neutral gas deficient’, rather than simply stating that it is highly ionized.
Further mappings reveal that the ionized pockets actually form a tunnel
that extends at least 820 light years towards Ursa Major, suggesting that it
might connect at least a thousand light years into the galactic halo.
As the research continues, it starts to become clear that our ‘local bubble’ was
actually part of a larger cylindrical cavity that pierces through the disk of
the galaxy, dubbed the ‘local chimney’. So how do they explain the formation of
the bubbles, and how can they explain the structure of the local chimney?
They believe supernova explosions are responsible for creating these voids.
In the case of the local chimney, they speculate that energetic supernova
explosions created fast-moving expanding bubbles of hot gas that collided with surrounding cold gas
of the interstellar space, which in turn became compressed into thin shells.
Eventually these shells of cold gas meet other expanding hot cavities and break
up, forming small tunnels or path- ways between the expanding voids.
Towards the center of the local chimney we find the Pleiades, and it is here that
astronomers search for the possible source of a supernovae. A little further out from these are a
belt of stars, called the Gould belt. These are massive hot OB-type stars. These
provide a clue as to what might be going on. The supposed young stars appear to form
a ring, centered on the Pleiades and have motions that appear to imply that they
are also orbiting around this point. Yet, there is not enough mass for this to be possible.
Let's just take a little step back here. Are we surprised that our Sun sits in a
bubble of ionized hydrogen? No, this is exactly what we would expect to find. Our Sun sits on a filament which
powers our star. The fact that this structure seems to
take on a cylindrical appearance, should also not come as a surprise.
So what are we to make of the boundary layer of cooler gas surrounding this structure?
Assuming that the filament takes on a simple Birkeland Current structure, we
would expect recombination to occur. Marklund identified this process and
showed that the elements will become preferentially sorted according to their ionization energy.
This means that hydrogen and helium would always be found towards the outer edge of the filament.
So comparing the density of hydrogen inside the filament to the outer edges,
you should see a sharp increase in the density, and the appearance of a wall.
If we examine this image, then we see that the areas in white are low density,
probably hot, ionized gas. So in other words, plasma. The darker colored areas are thought to
be cold dense gas, possibly largely molecular in nature. We can clearly see that many areas seem
to connect to each other, forming a sort of network. Now it is important to point out that
there is likely to be many smaller filaments connecting and overlapping,
creating this blurred white part of the image. From Jim Wenninger’s work on Arcturus, we
can see that the motion of the stars may reveal parts of this structure nearby us,
with us circling around the local Arcturus filament. Some astronomers have wondered if the
local bubble, or chimney system of the interlocking gaseous cavities is
characteristic of the entire Milky Way. Astronomers looking at an updated map of
cold local interstellar gas in the galactic plane, see an inner empty region with
finger-like extensions or tunnels that poke through the surrounding wall and
reach into the nearby regions of the galaxy. These regions are known to
contain large amounts of hot, ionized, low- density gas that can be detected at
radio and ultraviolet wavelengths. Right next to our local bubble,
astronomers have identified a new bubble called the Per-Tau shell. It is thought to extend for about 500
light years and spans two well-studied molecular clouds, called Taurus and Perseus.
Using a special technique, they were able to create three-dimensional maps of the
local cloud structures. If we examine the Chameleon molecular cloud, we can see a series of filaments
that seem to connect via a hub-like structure. With a void in the center, it is also physically
connected to the Musca dark cloud. The Taurus cloud extends between 131 and 168 parsecs.
When viewed from the top, you might be able to notice that it consists of two
layers, separated by about 10 to 15 parsecs. This layering is consistent with several
previous studies. Musca is a clear example of a filament on both the two-dimensional and
three-dimensional image. It is termed a dark cloud, meaning that
it contains a myriad of sub-micron sized solid particles, often referred to as
intergalactic dust grains. They tend to block out visible light, making them
appear dark. They are thought to be composed of largely molecular gas, rather
than containing ionized material. Ultraviolet starlight is considered the
main source of ionization in H2 regions, and in H1 regions it ionizes elements
with low ionization potentials. This has led to the belief that it is
the only ionizer and that in dark clouds, where starlight is absorbed, the
ionization may go down to zero. This is not necessarily correct, because
in many cases, most ionization of cosmic plasma is produced by hydromagnetic
transfer of kinetic energy into electrical currents which ionize.
One common theme that they identified, was a point I touched on earlier - the
creation of the atomic hydrogen envelopes around the molecular clouds.
They also discovered that the widths between the outer and inner envelopes
had a consistent ratio of 3.4. When they identified the radial density
profiles, they found that it was inconsistent with a filament driven only
by gravity, and was much better suited to one where the filaments were magnetized.
Previous studies of the structures of magnetic fields in the solar
neighborhood cloud, have found strong coupling between the gas column density
and the magnetic field orientation; which is consistent with the idea that
magnetic fields play an important role in structuring the interstellar medium
in and around, the local molecular cloud. Despite all of this, they still favor the
formation of bubbles through supernovae. If the galaxy is composed of a network
of filaments that carry slow moving ions these form magnetic fields that hold the structure together.
Hannes Alfven pointed out that these structures are capable of transferring
energy over vast distances, and dissipating the energy across the
double layer with a voltage drop. It is important to understand that the
current required to accomplish this, may very well consist of low energy particles.
The plasma and material in these areas is not simply mixed together through random collisions.
Plasmas have a tendency to produce large variations in the chemical composition.
One mechanism is due to the different laws of motion of the non-ionized and
ionized components of a magnetized plasma. The condensation of non-volatile
substances to grains, constitutes another separation mechanism. Any charged grains of dust, or ions, will
feel an attraction towards the filament. As they move towards the filament, if
they gain enough speed, they can cause non-ionized material to become ionized.
This is particularly so in areas where a pinch occurs. This can cause large areas of low
density to be created. At the same time Marklund convection will sort material into radial shells.
Together, these could explain the network of bubbles we see throughout our local neighborhood.
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