We have discussed the origin of Dark Matter and the fact that to date no one has ever
detected it. There are 3 alternative concepts that could explain the galaxy rotation problem
without the need for Dark Matter. Let's dive in and find out more...
Our first observations of galaxies showed them to be quite isolated from each other
in space. We had expected these galaxies to have an inverse square gravitational field,
meaning that as you move further from the centre the rotation should slow down. At the
centre of the galaxy, we do indeed see a good correlation to the inverse square law but
once we move a little further out this changes meaning the orbital velocities stay constant
as we move further out. Dark matter was invented to add additional mass around the galaxy to
account for this discrepancy.
Later observations showed that galaxies were not isolated in space, but rather 'strung'
together on filaments.
Don Scott considered that the galactic rotation problem could be solved by considering the
radial electric field of the filament that the galaxy resides in but this presents some
problems that might not at first be obvious. Don Scott's model of a Bessel function Birkeland
current demonstrated that the material inside these forms into concentric shells. This was
due to the fact that the magnetic field changed as you moved further from the axis of the
Birkeland current. This would mean that some of the material would flow in the forwards
direction and as you move further out this would change to a rotation around the axis
and if you kept moving further out this would eventually lead to a reverse flow and this
pattern would keep repeating. At the same time, the amount of material would steadily
decrease with the highest being near the centre. In order to solve the galaxy rotation problem
Don instead focusses on the radial electric field in the filament. This was based on the
idea that the charge density is at its most concentrated towards the centre of a filament
and steadily drops off. This creates a linear uniformly decreasing voltage profile and means
that as you move further out the voltage would steadily drop. I have previously covered this
concept and some of the outstanding issues with it a while ago, the link will be in the
description. In order to solve the galaxy rotation problem we now need to have the material
being attracted inwards only by this electric field and no longer following the concentric
shell model. The problem is that from Don's original paper it is not clear if he model
his Bessel function on an ion only stream or a mixed electron and ion stream. Most plasma
should contain both. In which case the net charge should be close to zero, so there should
be no radial electric field. If we assume that it is predominately an ion flow then
it should be obvious that the charge density would indeed be highest at the centre but
now the problem is that this becomes a point of repulsion not attraction. Maybe I'm missing
something in his explanation here as I don't see how both the concentric shells and the
radial electric field could be true. If we add Marklund convection into the equation
it becomes even more complex as now the material should bunch at each of the shells leading
to discrete jumps not a uniform electric field. Marklund convection also required both electrons
and ions to work. If we examine the rotation curve for the model where the material follows
the electric field we find it is a better match compared to gravity only and no dark
matter.
Anthony Perrat had a slightly different concept of how galaxies might form in a Plasma Universe.
Here two filaments essentially twist together and at the closest point a double layer forms
which cause material to be collected there. As the two filaments continue to twist around
each other their motion creates the spiral arms of the galaxies and the central bulge
is where the matter is compressed the most. If you are interested in understanding this
model in more detail I would suggest looking at the series I produced on these which will
be linked in the description below. Peratt was happy that at some stage gravity would
start to take over but he never model this component in his simulation. Could this model
account for the difference between the central bulge and the arms of the spiral galaxy? Now
there are still many open questions that this concept has which I have covered in a separate
video which will also be linked below.
What if the answer was much simpler than all of this. Jim Weninger pointed out the following
concept. When we consider the gravitational field of a galaxy due to it's symmetry, we
can consider that there is a centre of mass towards which the field will point at any
point away from it. Filaments are very different and are long thin structures that stretch
for millions of light-years. There is no centre of mass as this is distributed across the
entire length of the filament, instead, it is a line of mass. If we move away far enough
then it will start to approximate a point mass. What we need to consider is that the
galaxies are embedded within these filaments. Traditionally it has been convenient to consider
space empty. The space in between galaxies is ignored as it pales into insignificance
compared to the density of a galaxy. The problem is that these filaments form the backbone
that created the galaxies they are still there and this very low density, almost undetectable
matter stretches for millions of light-years.
The gravitational field of this matter in the cylinder has been ignored. Let's just
consider the gravitational field of only the mass in this cylinder. We can imagine that
the cylinder is sufficiently long that we do not have to worry about either end. Now
imagine that we are at the centre of the filament. At this point, we would feel an equal attraction
from the mass above, below and from each side. The net result would be a cancelling out of
all the forces. This means at the centre of the filament the gravitational forces from
the filament do not act. If we move slightly off-axis we see there is no real change to
the forces from the mass above or below us but when we examine the difference from one
side of the filament to the other we can see that there is now slightly less material on
the left and slightly more material on the right. The net result is that we feel a force
back towards the centre. As we move further out this net inward force will slowly grow
until it reaches a maximum at the edge of the cylinder. This is the opposite to what
you would expect if you were moving away from a body where the field falls of with an inverse
square law.
Assuming the galaxy forms close to the centre of the filament, the highest concentration
of matter would be at the centre, the mass from the filament would also cancel out from
each direction leaving an inverse square law.
As we move further from the centre the central concentration of mass fall off quickly and
we are off-axis from the filament meaning we would experience an increased pull from
the filament on the opposite side of the central bulge. The effect of this is that no matter
how much mass is concentrated in a galaxy and no matter how low the density of the filament
at some distance the gravitational field must go from inverse square law to an inverse law.
Now there are some important considerations from this idea. This material in the filament
would feel an attraction towards the central axis of the filament so we require some force
to stop this inward motion otherwise you would end up with all the matter concentrated in
long strings. The simplest way to achieve this would be through rotation of the material
in the filament, similar to how a galaxy works. Of course, if this material in the filament
was plasma we would instead need to consider the repulsive forces of these charges as well
as the longer-range attractive force that created the filament in the first place, through
the movement of the plasma. Here another consideration might be Don's Scott Bessel function model
as the concentric shells might act as confinement areas for some of this material. So could
a combination of these provide an alternative explanation for the existence of Dark Matter?
If we examine the galaxy rotation curve you will notice when we examine the one for our
Milky Way there appear to be bumps as it appears to speed up then slow down. This might be
explained by considering that Marklund convection would cause the material to bunch together
creating higher density rings as you move further out. Thereby altering the mass profile
and hence the gravitational field of the galaxy causing parts to rotate slower and faster?
Indeed evidence for this might be found in how the chemical composition of stars changes
as we move further out from the galactic centre.
The distribution of dark matter that is needed on the galactic scale to explain the rotation
problem means that we cannot have much of it here in our neighbourhood. This means that
we cannot use it to explain stellar rotation in our neighbourhood and yet they do! The
Gould Belt is a ring of stars that are centred on the Pleiades. I have discussed this as
part of the Precession series. Currently, astronomers struggle to explain its formation
but one of the leading theories was that a large Dark Matter Clump impacted a giant molecular
cloud forming a ring of stars. The inferred motion of the stars would seem to indicate
that they are orbiting a common centre which does not have enough mass. In Jim Weninger's
concept, the local chimney and the Gould belt were formed as part of a singular event when
the local Birkeland current underwent a pinching event at the galactic plane and pulled in
the surrounding material and then explosively ejected it outwards in a torus.
Then we have the dwarf galaxy problem, also known as the missing satellites problem. This
arises from a mismatch between the observed dwarf galaxy numbers and their simulations.
In these simulations, the dark matter clusters hierarchically, in ever increasing numbers
of halos. As an example, our Milky Way has 11 dwarf galaxies and yet the simulations
had predicted there should be around 500!
And herein lies another problem with Dark Matter on any single scale it can be used
to explain any type of rotation. The problem is that you then cannot take it out at that
scale and yet this is exactly what is being done. Consider this, if you are trying to
get funding for dark matter detectors, where are you going to propose this dark matter
is to be found... yes that's right, here in the Solar System, where we don't even seem
to have any breakdown in the inverse square law...