Questions on the enigmatic rotational curve of spiral galaxies

I just want to add a thought experiment to help us visualise what is being
suggested/asked.

Consider a number of stars arrayed in a line across space, say a few light
years in length.

Assuming the initial condition is one of a stationary motion of each star
relative to the other, what would we expect to occur next?

I assume that the mutual attraction of the stars will cause the row of stars
to shorten until they end up clumped together.

So to make my 'barred' galaxy stable I rotate it fast enough so that the
stars on the two ends don't proceed toward or away from the rotational
centre.

Will this work? I assume it will not work close to the rotational centre
but will work further out.

There is a greater gravitational pull on objects closer to the two ends
because there is more mass between those objects and the centre, but the
rotational speed is greater as well - nicely balanced

Now we add more mass to the centre. Objects toward the ends of the arms are
going to be drawn inwardly unless the arm describes an arc. Now the pull
directly from the central mass can be added to the less effective pull of
the curved arm and the galaxy is again stable.

Why do I think this has been missed?
Models consist of known and unknown quantities, such as the numbers of and
masses of the stars that can be observed. But unobserved is the central
mass which is estimated. The central mass, I assume, is estimated at far
higher than it actually is. I don't think modellers have considered
relatively tiny central masses, as in my barred galaxy model above. Thus a
higher central mass then requires a greater mass beyond the galaxy for it to
rotate as observed.

I do not have the skills to test these ideas but I assume that either:
It has already been considered and shown to be flawed/viable or
members of this list can estimate the viability of the idea using a
simplified model (as I have suggested above).

Robert

On 22 Feb, 12:11, "Robert Karl Stonjek"
wrote:
I just want to add a thought experiment to help us visualise what is being
suggested/asked.

Consider a number of stars arrayed in a line across space, say a few light
years in length.

Assuming the initial condition is one of a stationary motion of each star
relative to the other, what would we expect to occur next?

I assume that the mutual attraction of the stars will cause the row of stars
to shorten until they end up clumped together.

So to make my 'barred' galaxy stable I rotate it fast enough so that the
stars on the two ends don't proceed toward or away from the rotational
centre.

Will this work? *I assume it will not work close to the rotational centre
but will work further out.

There is a greater gravitational pull on objects closer to the two ends
because there is more mass between those objects and the centre, but the
rotational speed is greater as well - nicely balanced

Now we add more mass to the centre. *Objects toward the ends of the arms are
going to be drawn inwardly unless the arm describes an arc. *Now the pull
directly from the central mass can be added to the less effective pull of
the curved arm and the galaxy is again stable.

Why do I think this has been missed?
Models consist of known and unknown quantities, such as the numbers of and
masses of the stars that can be observed. *But unobserved is the central
mass which is estimated. *The central mass, I assume, is estimated at far
higher than it actually is. *I don't think modellers have considered
relatively tiny central masses, as in my barred galaxy model above. *Thus a
higher central mass then requires a greater mass beyond the galaxy for it to
rotate as observed.

I do not have the skills to test these ideas but I assume that either:
It has already been considered and shown to be flawed/viable or
members of this list can estimate the viability of the idea using a
simplified model (as I have suggested above).

http://www.google.co.uk/search?hl=en...tation&me ta=

All galaxies seem to contain a supermassive black hole. This seems to
be required from the point of view of stability. A number of
simulations have been performed.

http://www.mpa-garching.mpg.de/galform/

This is a website for one of the foremost groups.


- Ian Parker

"Ian Parker" wrote in message
...
On 22 Feb, 12:11, "Robert Karl Stonjek"
wrote:
Snip

I do not have the skills to test these ideas but I assume that either:
It has already been considered and shown to be flawed/viable or
members of this list can estimate the viability of the idea using a
simplified model (as I have suggested above).

http://www.google.co.uk/search?hl=en...tation&me ta=

All galaxies seem to contain a supermassive black hole. This seems to
be required from the point of view of stability. A number of
simulations have been performed.

http://www.mpa-garching.mpg.de/galform/

This is a website for one of the foremost groups.


- Ian Parker

Thanks, Ian,
The simulations are a little to big but the paper search is more
interesting. For instance in The method of Galactic Rotation
http://adsabs.harvard.edu/abs/1996A&AS..118...59J
the authors assume an instant propagation of gravity and the gravitational
pull of the galactic arm itself appears to be left out altogether.

My quick skim of several results leads me to conclude that the Kepler model
is the first approximation and this fits well with the inner region of a
galaxy eg 1pc for the Milky Way (the supermassive black hole accounts for
the motion of the inner objects). But the bar model may be a better
approximation for the outer region ie starting with evenly spaced massive
objects across, say 20kpc (comparable to the Milky Way) and then consider
the initial conditions of a static and rotating bar and see what happens.

The simplified model is the bread and butter of physics modelling, but the
sphere or disc may not be the best simplified model in this case. The bar
may be more instructive for the outer region.

Here is my objection clearly outlined in the abstract of another paper:
"Galaxies as rotating systems involve a balance of gravitational attraction
and centripetal force. When the central mass is dominant the dynamics,
referred to as Keplerian, are that the orbital velocities are proportional
to the inverse square root of the path radius. A plot of velocity vs. path
radius is a Rotation Curve. For galaxies viewed as the disk edge we see one
end moving toward us relative to the center and the other moving away. The
rotational velocities are measured from the variation in redshift along the
galactic diameter. Rotation curves so obtained are not the expected
Keplerian inverse square root; rather, [beyond the galactic core] they are
flat. In a solid sphere all parts move at rotational velocities directly
proportional to radius. Since the observed flat curves lie between the
Keplerian inverse square root of radius and the solid's direct proportion to
radius, a mass discrepancy is inferred -- that unseen matter is dispersed
throughout the galaxy, a halo of "dark matter" that causes the curve form
exhibited -- thus the "dark matter" hypothesis. The mass discrepancy only
appears where the acceleration is less than 10-8 cm/sec2. Modeling gives an
alternative hypothesis: Modification of Newtonian Dynamics or MOND, that
gravity and or inertia are modified when g or a is less than 10-8 cm/sec2.
No justification has been developed except correlation with the mass
discrepancies. An alternative explanation is presented -- the general
exponential decay of the overall universe, which has been analyzed and
developed in several papers. The universal decay accounts for the mass
discrepancies because the effect of the decay is to make the rotation curves
appear to deviate from the form expected in a Keplerian galactic disk
although the actual rotational behavior does not."
http://www.citeulike.org/group/48/article/70704

Referring back to my illustration at the root of this thread we note that
force '3' has been ignored.
I can't tell if the models on the page you point to consider those forces or
not.

Robert

On Feb 22, 7:40 am, "Robert Karl Stonjek"
wrote:
"Ian Parker" wrote in message

...
On 22 Feb, 12:11, "Robert Karl Stonjek"
wrote:
Snip

I do not have the skills to test these ideas but I assume that either:
It has already been considered and shown to be flawed/viable or
members of this list can estimate the viability of the idea using a
simplified model (as I have suggested above).

http://www.google.co.uk/search?hl=en...alactic+rotati...

All galaxies seem to contain a supermassive black hole. This seems to
be required from the point of view of stability. A number of
simulations have been performed.

http://www.mpa-garching.mpg.de/galform/

This is a website for one of the foremost groups.

- Ian Parker

Thanks, Ian,
The simulations are a little to big but the paper search is more
interesting. For instance in The method of Galactic Rotationhttp://adsabs.harvard.edu/abs/1996A&AS..118...59J
the authors assume an instant propagation of gravity and the gravitational
pull of the galactic arm itself appears to be left out altogether.

My quick skim of several results leads me to conclude that the Kepler model
is the first approximation and this fits well with the inner region of a
galaxy eg 1pc for the Milky Way (the supermassive black hole accounts for
the motion of the inner objects). But the bar model may be a better
approximation for the outer region ie starting with evenly spaced massive
objects across, say 20kpc (comparable to the Milky Way) and then consider
the initial conditions of a static and rotating bar and see what happens.

The simplified model is the bread and butter of physics modelling, but the
sphere or disc may not be the best simplified model in this case. The bar
may be more instructive for the outer region.

Here is my objection clearly outlined in the abstract of another paper:
"Galaxies as rotating systems involve a balance of gravitational attraction
and centripetal force. When the central mass is dominant the dynamics,
referred to as Keplerian, are that the orbital velocities are proportional
to the inverse square root of the path radius. A plot of velocity vs. path
radius is a Rotation Curve. For galaxies viewed as the disk edge we see one
end moving toward us relative to the center and the other moving away. The
rotational velocities are measured from the variation in redshift along the
galactic diameter. Rotation curves so obtained are not the expected
Keplerian inverse square root; rather, [beyond the galactic core] they are
flat. In a solid sphere all parts move at rotational velocities directly
proportional to radius. Since the observed flat curves lie between the
Keplerian inverse square root of radius and the solid's direct proportion to
radius, a mass discrepancy is inferred -- that unseen matter is dispersed
throughout the galaxy, a halo of "dark matter" that causes the curve form
exhibited -- thus the "dark matter" hypothesis. The mass discrepancy only
appears where the acceleration is less than 10-8 cm/sec2. Modeling gives an
alternative hypothesis: Modification of Newtonian Dynamics or MOND, that
gravity and or inertia are modified when g or a is less than 10-8 cm/sec2.
No justification has been developed except correlation with the mass
discrepancies. An alternative explanation is presented -- the general
exponential decay of the overall universe, which has been analyzed and
developed in several papers. The universal decay accounts for the mass
discrepancies because the effect of the decay is to make the rotation curves
appear to deviate from the form expected in a Keplerian galactic disk
although the actual rotational behavior does not."http://www.citeulike.org/group/48/article/70704

Referring back to my illustration at the root of this thread we note that
force '3' has been ignored.
I can't tell if the models on the page you point to consider those forces or
not.

Robert


May I add a thought?

The Milky Way is about a hundred thousand light years across.
Let's take this as about average.

Now, if I am looking at a similar galaxy out
in space, won't I be seeing the front edge as
it was positioned at Time X in the same image
as the back edge as it was positioned at
Time X minus 100,000 years?

So why are galaxies all so
symmetrical? Shouldn't they all be
skewed in a way that reflects their
movement and our position and the difference
between when light arrives to us from
their closest and farthest parts relative to us?

john

On 22 Feb, 13:40, "Robert Karl Stonjek"
wrote:


Thanks, Ian,
The simulations are a little to big but the paper search is more
interesting. *For instance in The method of Galactic Rotationhttp://adsabs.harvard.edu/abs/1996A&AS..118...59J
the authors assume an instant propagation of gravity and the gravitational
pull of the galactic arm itself appears to be left out altogether.

There is always the question about the validity of assumptions.
Instantanious travekl for gravity can be defended on the basis that
the errors in that approximation are of the order of rotation
velocities relative to c.

Now the Sun is travelling at 600km/s c = 300,000km/s. Hence the
instantaneous travel of gravity can be justified. The velocities of
the stars relative to each other are lower still.

What is in fact more serious is assumptions about "dark matter".


- Ian Parker

On Feb 22, 7:27*am, Ian Parker wrote:
On 22 Feb, 13:40, "Robert Karl Stonjek"
wrote:



Thanks, Ian,
The simulations are a little to big but the paper search is more
interesting. *For instance in The method of Galactic Rotationhttp://adsabs.harvard.edu/abs/1996A&AS..118...59J
the authors assume an instant propagation of gravity and the gravitational
pull of the galactic arm itself appears to be left out altogether.

There is always the question about the validity of assumptions.
Instantanious travekl for gravity can be defended on the basis that
the errors in that approximation are of the order of rotation
velocities relative to c.

Now the Sun is travelling at 600km/s c = 300,000km/s. Hence the
instantaneous travel of gravity can be justified. The velocities of
the stars relative to each other are lower still.

Uh, no. Gravitational effects travel exclusively at c in GR, and this
has been shown to be consistent with reality in observation.


What is in fact more serious is assumptions about "dark matter".

* - Ian Parker

On 22 Feb, 19:52, Eric Gisse wrote:
On Feb 22, 7:27*am, Ian Parker wrote:





On 22 Feb, 13:40, "Robert Karl Stonjek"
wrote:

Thanks, Ian,
The simulations are a little to big but the paper search is more
interesting. *For instance in The method of Galactic Rotationhttp://adsabs.harvard.edu/abs/1996A&AS..118...59J
the authors assume an instant propagation of gravity and the gravitational
pull of the galactic arm itself appears to be left out altogether.

There is always the question about the validity of assumptions.
Instantanious travekl for gravity can be defended on the basis that
the errors in that approximation are of the order of rotation
velocities relative to c.

Now the Sun is travelling at 600km/s c = 300,000km/s. Hence the
instantaneous travel of gravity can be justified. The velocities of
the stars relative to each other are lower still.

Uh, no. Gravitational effects travel exclusively at c in GR, and this
has been shown to be consistent with reality in observation.

I never said they did not. What I DID say was that the error involved
is proportional to relative velocities/c. (assuming travel at c). If a
lot of calculation is involved you may assume instantaneous travel for
orbital velocities of 600km/s and relative velocities lower still.


- Ian Parker

On Feb 22, 7:11*am, "Robert Karl Stonjek"
wrote:
I just want to add a thought experiment to help us visualise what is being
suggested/asked.

Consider a number of stars arrayed in a line across space, say a few light
years in length.

Assuming the initial condition is one of a stationary motion

"stationary motion"?

AHAHAHAHAHAHAHAHA

Tom Davidson
Richmond, VA

wrote in message
...
On Feb 22, 7:11 am, "Robert Karl Stonjek"
wrote:
I just want to add a thought experiment to help us visualise what is being
suggested/asked.

Consider a number of stars arrayed in a line across space, say a few light
years in length.

Assuming the initial condition is one of a stationary motion

"stationary motion"?

AHAHAHAHAHAHAHAHA

Tom Davidson
Richmond, VA

RKS:
OK, I was thinking of writing either 'stationary' or 'no motion' and ended
up with an insane hybrid.

Thanks for pointing out the error (I think...)

Robert

On Feb 22, 7:03*pm, "Robert Karl Stonjek"
wrote:
wrote in message

...
On Feb 22, 7:11 am, "Robert Karl Stonjek"
wrote:

I just want to add a thought experiment to help us visualise what is being
suggested/asked.

Consider a number of stars arrayed in a line across space, say a few light
years in length.

Assuming the initial condition is one of a stationary motion

"stationary motion"?

AHAHAHAHAHAHAHAHA

Tom Davidson
Richmond, VA

RKS:
OK, I was thinking of writing either 'stationary' or 'no motion' and ended
up with an insane hybrid.

Thanks for pointing out the error (I think...)

Robert

xxein: You may be overlooking a serious problem. I was thinking of
the different galaxial types and began wondering if age is a major
factor. Elliptical becomes more disk-like, spiral, bar and then to
ring.

But more interesting is how the gasses and stars revolve at the top or
bottom of the (early?) elliptical ones. Definitely not any
classically described revolution.

So a thought came to me (inspired by your bars). What guides these N
and S stars to form and retract toward the hub and/or rotational disk
(flatten out)?

I know there are a lot of parameters to form galaxies in the first
place, such as the local richness of matter and how it can deviate
from the overall universal expansion radial and a few other things.

But (back to your bars), these top and bottom (N and S) stars and
gasses must feel the presence of each other's position and motion in
such a spherical primordial stage of a galactic formation.
Imperfections give the galaxy a starting rotational velocity and the
rest is the evolutionary history.

Sounds a little too easy. I know. But it all ties into the halo
effect. Halo stars are the oldest associated with any galaxy. They
simply existed in an imperfect group caused also by imperfection in
the distribution of primordial matter. By their position and gravity
they can form discriminant gravitational groups over time. They can
cause an internal gravitational lensing effect. It depends on the
difference in scales between available matter and where they formed.
This difference need only tip a delicate balance. Energy seeks an
equilibrium. It almost never achieves this because of motion. Within
a raggedy group of halo stars, there is originally made a sort of
vacuum deficient of energy because the halo's aggregate gravity was
pulling the energy out. As the halos grew with energy, they shrank
toward each other and pulled more energy in from the outside. Since
they hardly constitute a continuous spherical shell, they continuously
infused their rough interior with more and more non-captured/consumed
energy. So the energy (matter) began to become more dense in the
interior and a galaxy could eventually form by being so entrapped.

Sound better? I don't know if there are halo stars associated with
every galaxy formation. Maybe they got swept into the galaxy itself
and are hard to find or got assimilated to the core/BH during the
evolution of the galaxy. Beats me.

But if halo stars are associated with galaxy formation, they will
appear to remain outside of them in earlier stages of a galaxy's life.

Back to the revolution of stars and an early galactic morphology, if
you simply consider any radian as a 'bar', the diffuse gravitational
effects are very important since the galaxy is building a rotational
momentum.

An additional factor (just considered) is that it is at the galactic
level in cosmology the universal expansion effects first appear. This
prompts me to think of what happens to a galaxy that has insufficient
energy in it's environment to run itself. When a star has to fall
back into itself, it can mean one of three things (the three bears
tale). It has grown to big and too fast for it's britches because of
rich environment (Super-nova type), it becomes a BH because it
maintains a not-so-large feeding schedule or it collapses of
starvation (nova). Neither of these may necessarily be really true,
but it got me to thinking what primordial galaxies would do if cut off
from outside energy. Would they eventually collapse into their
centers and give us quasars? Maybe they met with other universes and
got too hot to handle like a super-fed galaxy. Would we see the same
galaxy as a quasar if we were viewing it from the other universe(s)?
Never mind.

Now maybe with my reply and your 'bar' effect you can show how the
Pioneer anomaly works.