[Dave Lev (OP)]

Please look at the following article:
https://www.space.com/19915-milky-way-galaxy.html
"Spiral arms are like traffic jams in that the gas and stars crowd together and move more slowly in the arms. As material passes through the dense spiral arms, it is compressed and this triggers more star formation," said Camargo.

So, our scientists belive that stars don't stay at spiral Arms but they just move slower at the arms.
Therefore, all the stars actually cross the arms while they orbit around the galaxy.
The article didn't say that.  It explains that the stuff moving through the arms is slowed by friction, and thus tends to more or less stay in the arms.  That seems to be why there are arms and not a homogeneous fog without structure.
Nothing in that article suggests that all stars do a certain thing.

The article says that stars and gas are slowed (by friction) to a lower speed relative to the arm, not relative to the galaxy.  The whole galaxy moves at about 217 km/sec at this radius, and things moving at a different speed tend to match the local speed due to collisions with the thick material.

Well, it is stated: "As material passes through the dense spiral arms"
How could they stay at the arm if they passes through?
What do you understand from the idea of "passes through"?
In any case, if stars stay at the Arms (all the time from day one), than why is it?
Does it mean that they hold each other by gravity force?
If so, that exactly the whole idea which I have presented.
If they don't hold each other by gravity force, why they stay at the Arm?

[Halc]

In any case, if stars stay at the Arms (all the time from day one), than why is it?
Does it mean that they hold each other by gravity force?
If so, that exactly the whole idea which I have presented.

I never disagreed with that.  Yes, gravity (and friction) seems to be what holds them together, just like those two effects are what hold a solar system together.

You've expressed denial of dark matter, in which case the acceleration of any material in the galaxy (the arms in particular) is unexplained by your assertions.   Without dark matter, there is simply not enough gravitational force generated by the remaining matter at the observed distances to explain the acceleration needed to maintain a 217 km/sec orbital speed around the galaxy that is observed for all material in any galactic arm at this radius.

[Dave Lev (OP)]

In any case, if stars stay at the Arms (all the time from day one), than why is it?
Does it mean that they hold each other by gravity force?
If so, that exactly the whole idea which I have presented.

I never disagreed with that.  Yes, gravity (and friction) seems to be what holds them together, just like those two effects are what hold a solar system together.

So, you agree that the stars hold each other in the arm due to gravity (or friction if you like)
Therefore, do you agree that in this case each star must obey to the local gravity force in the Arm?
It is similar to the Earth/sun gravity force.
The Earth doesn't care about the gravity forces on the Sun. It is just holds/orbits the Sun by gravity force and follows it where ever it goes.
So, as we do not set the calculation why the Earth orbits around the galaxy, we also shouldn't worry why the sun orbits around the galaxy.
The Sun holds itself in the spiral arm.
Where ever the spiral arms goes - the Sun goes.
So, we have to find why/how the spiral arm orbits the galaxy and not why the Sun orbits the galaxy.
Only if the Sun is disconnected from the arm, than we must look for dark matter.
As long as is connected in the arm due to gravity, we must look for answers about the arm
We might find that Dark matter is needed for the Arm, but there is no need to find an explanation for the Sun - as long as it is connected to the arm by gravity.
In the same token - as long as the Earth is connected to the Sun by gravity force, we do not need to find an explanation why the Earth orbits around the galaxy.

As I have stated – Gravity works locally:
Another example -
An asteroid orbits around the Moon. Hence, the moon holds this asteroid by gravity.
The moon orbits around the Earth. Therefore, the Earth holds the Moon which holds the Asteroid by gravity.
So, we can continue at higher hierarchy. But at the end we might find that the asteroid orbits the Galaxy.
However, as long as the asteroid is connected by gravity to the moon, we do not try to find a direct explanation why it orbits the galaxy at supper high orbital velocity (with reference to the galaxy)
In the same token, as long as the Sun is connected to the arm by gravity force, we do not need to find a direct explanation why it orbits the galaxy.
As I have already explained - The sun orbits around a local virtual host point. Hence, we can say that the Sun holds itself to this virtual host point by gravity force (Local gravity force).
However, this virtual Sun' host point holds itself in the spiral arm by gravity force.
Therefore, at this phase, we must find the answer for – "Why the Arm orbits around the galaxy (and not why the sun orbits around the galaxy)"?
Do you agree with that?

[Halc]

Yes, gravity (and friction) seems to be what holds them together, just like those two effects are what hold a solar system together.

So, you agree that the stars hold each other in the arm due to gravity (or friction if you like)

Not 'or friction'.  It takes both.  Without the latter, something not part of the arm may be accelerated by the gravitational pull of a nearby arm, and that thing will thus have greater than escape velocity of the arm.  It will pass through and not come back.  Friction changes that.  It bumps into stuff and slows relative to the material it hits, as described in that recent link you posted.  This keeps it from leaving, and makes it part of the arm.  Dark matter (WIMPs) in particular have no friction, and are thus not particularly bound to the arms.

Therefore, do you agree that in this case each star must obey to the local gravity force in the Arm?

You keep asking this.  Each star's velocity and acceleration is determined by the sum of the force vectors acting upon it.  This is all things, not just local ones.

It is similar to the Earth/sun gravity force.

Yes.  Earth is pulled by all things, not just local ones.

The Earth doesn't care about the gravity forces on the Sun. It is just holds/orbits the Sun by gravity force and follows it where ever it goes.

Not necessarily.  It only works predictably if there are no other objects that exert gravitational force on Earth, and that is not true.  Yes, for the most part, we can reasonably assume Earth will follow the solar system.

So, as we do not set the calculation why the Earth orbits around the galaxy, we also shouldn't worry why the sun orbits around the galaxy.
The Sun holds itself in the spiral arm.
Where ever the spiral arms goes - the Sun goes.

The arm is not an object like the sun is to Earth.  The arm is a smear of matter, all moving at different orbits about the galaxy.  Some of it goes around in much less time than parts further out.  It isn't one thing that the sun follows.

So, we have to find why/how the spiral arm orbits the galaxy and not why the Sun orbits the galaxy.

Sure.  That's the part you cannot explain.  The arm (all parts of it) has acceleration that is incompatible with Newton's laws and your assertions.  Either your assertions are wrong, or Newton is.

Only if the Sun is disconnected from the arm, than we must look for dark matter.

Why?  The sun has the same path as all the rest of the arm at this radius.

As long as is connected in the arm due to gravity, we must look for answers about the arm
We might find that Dark matter is needed for the Arm, but there is no need to find an explanation for the Sun - as long as it is connected to the arm by gravity.

Nobody claims that dark matter explains the sun's attraction to the arm.  Dark matter is not concentrated in the arms, and so has little to do with the cohesive properties of the arms.

In the same token - as long as the Earth is connected to the Sun by gravity force, we do not need to find an explanation why the Earth orbits around the galaxy.

An asteroid orbits around the Moon. Hence, the moon holds this asteroid by gravity.
The moon orbits around the Earth. Therefore, the Earth holds the Moon which holds the Asteroid by gravity.
So, we can continue at higher hierarchy.

This is fine, but if the sun was not there, you still would have to explain why the Earth goes around the nothing where the sun is supposed to be.  You're right, you don't need to discuss the asteroid going around the moon.  You can treat the whole thing as a unit.  Doing so does not explain the acceleration of the collection.

Therefore, at this phase, we must find the answer for – "Why the Arm orbits around the galaxy (and not why the sun orbits around the galaxy)"?
Do you agree with that?

With minor edits, sure.  We must ask why the local portion of the arm orbits around the galaxy at the speed it does. Not why it goes around, but why so fast? It accelerates at about 2e-10 m/sec˛ and the mass of the matter we see in the galaxy is not enough to explain that acceleration.

We know why the arm orbits:  Things just do when there is a mass to orbit, such as the material that makes up the inner portion (stuff closer than us) of the galaxy.  But orbital speed is very much a function of the mass of that material, and there apparently isn't enough of it.

[Dave Lev (OP)]

You keep asking this.  Each star's velocity and acceleration is determined by the sum of the force vectors acting upon it.  This is all things, not just local ones.

Yes and No.
Yes - based on theoretically point of view.
No - based on real evidences.
Please look at our moon.
The Gravity force of the Sun/Moon is stronger by more than a twice with regards to the Earth/Moon.
If the Moon had to chose its orbital path based on the sum of the force vectors acting upon it, it will had to orbit around the Sun instead around the Earth, however - this isn't the case.
So, even if the Sun/Moon gravity is stronger than Earth/moon gravity, the moon prefers to orbit around a local host (Earth).
Therefore, as I have stated, Gravity works locally.
In the same token - we can say about the Earth.
Our scientists claim that  more than 100 Billion Sun mass is needed to be at the orbital center of the Sun (in the galaxy) in order to hold the Sun in its orbital path.
If we try to calculate the Galaxy/Earth gravity force (based on that mass), we should find that it is much higher than Sun/Earth gravity force.
So, Based on a pure sum of the force vectors acting upon the earth, it had to ignore the Sun and start running around the galaxy. But again - this isn't the case.
Hence, as the Earth had selected a local mass (our Sun) instead of the galaxy, and as the Moon had selected the Earth instead of the Sun; we have to claim the following:
Each object's velocity and acceleration is mainly determined by the local mass and not by the sum of the force vectors acting upon it.
The sum of the the force vectors could set a tidal. No more than that (Assuming that there is no collision)!!!
 

The arm is not an object like the sun is to Earth.  The arm is a smear of matter, all moving at different orbits about the galaxy.  Some of it goes around in much less time than parts further out.  It isn't one thing that the sun follows.

We have already discussed this issue.
Each star orbits around a local virtual host point. Therefore, although we see that all the stars are moving in different directions, their host points are very stable with regards to each other.
Hence, The Arm Is an ARM. It holds all the Virtual host points at the arm due to local gravity force.
This is the key element of spiral arm.
If the arm can't hold the stars, than by definition the stars must cross the arm and get out of it.
You can't just say that the stars stay at the arm but the arm doesn't hold them by gravity.
This is none realistic statement.

In the same token - as long as the Earth is connected to the Sun by gravity force, we do not need to find an explanation why the Earth orbits around the galaxy.

Sorry - this is incorrect. We can't take it for granted. We need to find an explanation why the Earth orbit around the Sun although its gravity force is lower than the Gravity force of the galaxy.
I will give you a tip - Gravity Works locally.
This is the ultimate answer for:
Why the moon holds/orbits around the Earth instead of the Sun?
Why the Earth Holds/orbits around the Sun instead of the galaxy?
Why the Sun orbits around a virtual host point that holds itself in the arm due to Local gravity force?
If you still don't want to accept the great impact of "local gravity force" than try to explain why the moon orbits around the earth instead of the Sun.

With minor edits, sure.  We must ask why the local portion of the arm orbits around the galaxy at the speed it does. Not why it goes around, but why so fast? It accelerates at about 2e-10 m/sec˛ and the mass of the matter we see in the galaxy is not enough to explain that acceleration.

We know why the arm orbits:  Things just do when there is a mass to orbit, such as the material that makes up the inner portion (stuff closer than us) of the galaxy.  But orbital speed is very much a function of the mass of that material, and there apparently isn't enough of it.

The answer is very simple - Gravity works locally.
If you agree with that - you have got the answer!!!
There is no need for dark matter in the galaxy to hold the Sun in the orbital path around the center.
All we need is - Gravity works locally in the arm (and everywhere).

[Halc]

Each star's velocity and acceleration is determined by the sum of the force vectors acting upon it.  This is all things, not just local ones.

Yes and No.
Yes - based on theoretically point of view.
No - based on real evidences.

The theory was based on that real evidence.  If you have evidence to the contrary, that would counter 4 centuries of physics.

Please look at our moon.
The Gravity force of the Sun/Moon is stronger by more than a twice with regards to the Earth/Moon.
If the Moon had to chose its orbital path based on the sum of the force vectors acting upon it, it will had to orbit around the Sun instead around the Earth, however - this isn't the case.

Your understanding of orbital mechanics needs a lot of work.  The strongest force acting on the moon is from the sun, and that means that at all times, the moon accelerates towards the sun.  That's the implication of what I've said above.  I did not say the moon cannot orbit Earth.  The moon has no choice or preference about this.  It moves exactly as per forces as described by Newton.

Our scientists claim that  more than 100 Billion Sun mass is needed to be at the orbital center of the Sun (in the galaxy) in order to hold the Sun in its orbital path.
If we try to calculate the Galaxy/Earth gravity force (based on that mass), we should find that it is much higher than Sun/Earth gravity force.

How do you figure that?  No scientist claims this.  It is in fact 7 orders of magnitude lower.

So, Based on a pure sum of the force vectors acting upon the earth, it had to ignore the Sun and start running around the galaxy. But again - this isn't the case.

Wrong several ways.
First, the Earth does orbit the galaxy, having gone around nearly 20 times.
Secondly, there is no law that says a greater force will strip Earth away from the sun since the sun would also be subject to that force. This is why the moon orbits Earth despite Earth exerting less force upon it than the sun.
Thirdly, the sun contributes more to Earth's force vector than all other forces combined.

Each star orbits around a local virtual host point.

So you claim, but you've provided no mathematics for this claim.  How much force is applied by this virtual host point?  How might that be computed?  It needs to work for more than two bodies.  The motion of a two-body system can be reduced to a one-body case and thus has a solution.
Your claim is not similarly backed and is thus no more than a hand-waving assertion.
This is typical of armchair physicists.  All magical claims but no mathematics or predictions.

Therefore, although we see that all the stars are moving in different directions, their host points are very stable with regards to each other.
Hence, The Arm Is an ARM. It holds all the Virtual host points at the arm due to local gravity force.
This is the key element of spiral arm.

If it was the ARM, it would be the host point, and all the orbiting stuff would orbit that point.  It doesn't.  An arm is a smear with all different angular velocities about the galaxy.  This has been measured.

If the arm can't hold the stars, than by definition the stars must cross the arm and get out of it.

By definition?  What definition would that be?

You can't just say that the stars stay at the arm but the arm doesn't hold them by gravity.
This is none realistic statement.

But I didn't say that.

Sorry - this is incorrect. We can't take it for granted. We need to find an explanation why the Earth orbit around the Sun although its gravity force is lower than the Gravity force of the galaxy.

Even if the galaxy did exert this greater force, Earth would still probably orbit the sun.

I will give you a tip - Gravity Works locally.

F = GMm/r˛.  That is not local.  That says there is force at any distance.

There is no need for dark matter in the galaxy to hold the Sun in the orbital path around the center.
All we need is - Gravity works locally in the arm (and everywhere).

How do you explain the acceleration of the arm?  That's the thing you keep evading, post after post.

[mad aetherist]

The answer is very simple - Gravity works locally.  If you agree with that - you have got the answer!!!   There is no need for dark matter in the galaxy to hold the Sun in the orbital path around the center.  All we need is - Gravity works locally in the arm (and everywhere).

Gravity is the due to the acceleration of aether (ie aetheons) into mass where the aether is annihilated.
But aether does not possess any quantum mass or quantum anything -- but it is good at transmitting force to & from tween quantum mass -- the transmission being by way of reverberations of pulses that travel at over 20 billion c (hencely 1 gravity-second is equal to more than 634 light-years)(taking less than 236 sec to cross the 150,000 LY diameter of the Milky Way)(praps less than 1 sec). 

Hencely the shape of the disposition of cosmic mass in the Milky Way & near the particular stars of interest is important re the action & effect & magnitude of gravity & of big G especially re orbits (moreso than it might appear by the naive use of Newton's equation) -- & the disposition of nearby galaxies has an effect.
In other words gravity is due to tension in the aether, but this is a 3D thing, & hencely the attraction tween two stars needs other stars in every direction otherwise their mutual (2D) attraction will be limited.

When Cavendish did his big G experiment he had the mass of the Earth beneath & the mass of the building next to & above.  This ruined his results.  And nowadays silly Einsteinians try to make use of big G in a galactic environment, & need to invent Dark Matter.  No, Cavendish's big G works best (sometimes) on Earth, in a lab.

The centrifuging of aether near a spinning disc or in&near a spinning spiral galaxy gives a quasi-gravity that allso helps towards bringing about a 1/R relationship rather than the naive  1/RR Newtonian.  And quasi-gravity is a major reason why galaxies (& solar systems)(& Saturn's rings) like to have a disc shape.

[Dave Lev (OP)]

Please look at our moon.
The Gravity force of the Sun/Moon is stronger by more than a twice with regards to the Earth/Moon.
If the Moon had to chose its orbital path based on the sum of the force vectors acting upon it, it will had to orbit around the Sun instead around the Earth, however - this isn't the case.

Your understanding of orbital mechanics needs a lot of work.  The strongest force acting on the moon is from the sun, and that means that at all times, the moon accelerates towards the sun.  That's the implication of what I've said above.  I did not say the moon cannot orbit Earth.  The moon has no choice or preference about this.  It moves exactly as per forces as described by Newton.

O.K
We have to ask
"The sun attracts the moon with a force twice as large as the attraction of the earth on the moon. Why does the moon not revolve around the sun?"

Please look at the following article:
https://www.quora.com/The-sun-attracts-the-moon-with-a-force-twice-as-large-as-the-attraction-of-the-earth-on-the-moon-Why-does-the-moon-not-revolve-around-the-sun
"Here the moon and earth form a system, which is like a Binary system . If two astrologers rotate around their center of gravity together, then it is called binary system"
The answer is: "Binary system"
So, this binary system is a "local gravity force" that gives the moon/earth system the possibility to orbit around the Sun.
Hence, the noon is not their by itself, as the earth is not their by itself.
Now they both can orbit around the Sun.
But it is clear that without setting a binary system with the Earth - Just based on pure gravity force - the moon will prefer to orbit around the Sun.
It will never ever set a binary system with the earth if it was orbiting around the Sun.
Few words about binary-and-multi-star-systems:
https://stardate.org/astro-guide/binary-and-multi-star-systems
"A binary is a pair of stars that orbit each other. A multi-star system consists of three or more stars. The stars in a binary or a multi-star system all formed from a single cloud of gas and dust, so they are true “siblings.”"
The Earth & the Moon are real "siblings". This is a key element. I will explain later on why the current concept of how the Moon had been created is absolutely unrealistic:
https://en.wikipedia.org/wiki/Giant-impact_hypothesis
"The giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact suggests that the Moon formed out of the debris left over from a collision between Earth and an astronomical body the size of Mars, approximately 4.5 billion years ago"
I will also explain how the earth and the moon had been formed "from a single cloud of gas and dust, so they are true siblings". and why they set this binary system due to gravity force.
But in order to explain it, we must know how our galaxy really works.
The spiral arm is a key element in our discussion.
Therefore, understanding the gravity force between the objects in the arm is vital.
So, the Earth/moon is a binary system which holds them both while they orbit around the Sun.
In the same token, the arm is a multi-star-system.
Each star in the galaxy has its own virtual host point. Together, those host points set that "multi-star-system" which holds all the neaby stars in the arm.
So, the sun is not there by itself, (as the moon is not there by itself)
There is a local system that is bounded by gravity force.
Therefore, I call that Binary/multi-star-system as "local gravity force" which is the base for what we see.

[Halc]

We have to ask
"The sun attracts the moon with a force twice as large as the attraction of the earth on the moon. Why does the moon not revolve around the sun?"

As I've said, it does go around the sun, once per year, just like Earth.  So you want to know why the two (Earth and moon) don't separate due to the greater gravitational force of the sun.

Please look at the following article:
https://www.quora.com/The-sun-attracts-the-moon-with-a-force-twice-as-large-as-the-attraction-of-the-earth-on-the-moon-Why-does-the-moon-not-revolve-around-the-sun

Ouch.  This is why I rarely go to quora for answers.  I counted well over a dozen serious errors in that article.  This gem for example:
"Earth's mass and size are big so we do not understand the rotation of the earth. But this is not the case even between Jupiter and Sun. Here the sun does not turn around like Jupiter, and the Sun also does not turn around Jupiter!"
Apparently Earth is too large to understand if it orbits the sun or not, but Jupiter is small enough that it doesn't???  What?  It doesn't help that the guy apparently lacks English skills, but really, what was he trying to say with that statement?

"Here the moon and earth form a system, which is like a Binary system . If two astrologers rotate around their center of gravity together, then it is called binary system"

Do they have to be astrologers?  What if two physicists rotate around their common center of gravity?
If the two astrologers were anywhere near a significant mass like the moon, they would not orbit each other.  Binary systems are not always stable, and the one described there is incredibly unstable.  We need to ask why the Earth-moon system is more stable than the pair of astrologers.

The answer is: "Binary system"
So, this binary system is a "local gravity force" that gives the moon/earth system the possibility to orbit around the Sun.

Sure.  They're the only two significant masses in that system.  The sun's gravity does not act to separate them.  The non-uniformity of the sun's gravity does, and that non-uniformity is far less between the Earth and moon that is the acceleration of the moon due to Earth.  That's why the two stay together.

Hence, the noon is not their by itself, as the earth is not their by itself.

That article denies that the Earth is not by itself.  The orbit of Earth is depicted as a perfect circle, apparently unaffected by the pull of the moon.  Yet another mistake.  It also shows the moon curving away from the sun at times, another mistake if the sun's force is greater than the Earth's.  We can forgive these things since the diagrams are clearly not to scale.

But it is clear that without setting a binary system with the Earth - Just based on pure gravity force - the moon will prefer to orbit around the Sun.
It will never ever set a binary system with the earth if it was orbiting around the Sun.

Not true.  It is orbiting the sun, and yet it forms a binary pair with Earth.  The sun's gravitational field is too uniform at this radius to separate the two, just like the pull of the galaxy is far too uniform to pull the arms apart.  The pull from the sun goes up as the radius drops.  Venus has more acceleration than does Earth for this reason.  Not so with the galaxy according to your graphs.  The net acceleration (proportional to net force) actually goes down as the radius decreases.  This seems to be why galaxies form arms but new solar systems don't seem to.  Maybe they do at first.  Not like we can see that.

Few words about binary-and-multi-star-systems:
https://stardate.org/astro-guide/binary-and-multi-star-systems
"A binary is a pair of stars that orbit each other. A multi-star system consists of three or more stars. The stars in a binary or a multi-star system all formed from a single cloud of gas and dust, so they are true “siblings.”"

We are true siblings with many (all?) of the stars closest by, but we're not really a multi-star system.  Maybe we are.  Not sure.  The rule is not always true.  Some multi-star systems are made up of stars that didn't come from the same cloud of dust.  Maybe one system captured a passing star from somewhere else, a sort of adopted star, not a true sibling.  A single star probably cannot capture another, but any multi-star system is quite capable of it.

The stability of systems with more than two significant masses is low.  There are no 'host points', so the paths are unpredictable, and such systems are capable of ejecting stars from the family in a way that a binary system would not.

The Earth & the Moon are real "siblings". This is a key element. I will explain later on why the current concept of how the Moon had been created is absolutely unrealistic:

Well, other moons on other planets are not real siblings in that they formed from the same material.  So their history of being siblings doesn't explain the orbit or lack of it.  Yes, we went up there and found the moon to be the same stuff as us, thus forming the idea that it is a chunk of Earth knocked off or spun off.

"The giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact suggests that the Moon formed out of the debris left over from a collision between Earth and an astronomical body the size of Mars, approximately 4.5 billion years ago"
I will also explain how the earth and the moon had been formed "from a single cloud of gas and dust, so they are true siblings". and why they set this binary system due to gravity force.

Being formed by a whack is quite different than forming separately from a common cloud.  The latter hypothesis is unlikely.  Still, Pluto has a moon even more disproportionately large, and that one doesn't appear to be the same material.  Unclear on the history of those two.

But in order to explain it, we must know how our galaxy really works.
The spiral arm is a key element in our discussion.
Therefore, understanding the gravity force between the objects in the arm is vital.
So, the Earth/moon is a binary system which holds them both while they orbit around the Sun.
In the same token, the arm is a multi-star-system.
Each star in the galaxy has its own virtual host point.
Together, those host points set that "multi-star-system" which holds all the neaby stars in the arm.

You've not explained this host point mechanics, and thus it is just fantasy.  It can be trivially demonstrated with a simulation of 3 or more stars, none of which will exhibit motion about a host point. You can deny the Newtonian forces upon which that simulation would run, but you've not described new laws to replaces the ones you're denying.

Sure, arms hold themselves together via gravity.  That is pretty simple since force (towards galactic center) goes up at the outside edge of the arm, and force (towards galactic center) goes down on the inside edge.  This is very different from Earth/moon where the sun's pull is greater, not less, at the inside edge.  So arm stability can be explained without this host-point nonsense.

None of how the arms hold together is relevant to the question of the acceleration of the arm itself, which is totally unexplained in your posts.

[Halc]

"If two astrologers rotate around their center of gravity together, then it is called binary system"
If two astrologers are in mutual orbit, how will they determine which sign is prominent at a given time?  They lack an obvious 'nighttime' to make that determination, so they only have each other to reference, meaning they'll be off 6 months from each other, despite the unspecified length of their orbital period.

[Dave Lev (OP)]

Sure, arms hold themselves together via gravity.  That is pretty simple since force (towards galactic center) goes up at the outside edge of the arm, and force (towards galactic center) goes down on the inside edge.

Dear Halc
If you agree with that, than this is all is needed to explain the spiral arm structure.
As I have stated, each star is connected in the arm by Newton gravity force.
All the stars have a similar orbital speed. (More or less)
Therefore, for any time frame, they all cross the same distance.
In order to achieve it, as they drift outwards, they also drift backwards.
That activity sets by definition the spiral shape of the arms.

That is the whole idea about spiral arms.
Now, let's try to find what our scientists have to say about: "How Our Milky Way Galaxy Got Its Spiral Arms"
https://www.space.com/24642-spiral-galaxies-milky-way-shape-explained.html
Dated - February 12, 2014
"The researchers found that the universe was a very chaotic place in its infancy. The first galaxies were disks with massive, bright, star-forming clumps and little regular structure. To develop the nice spiral forms seen today, galaxies first had to settle down, or "cool," from the previous chaotic phase. This evolution took several billion years."

First contradiction - "Massive disc galaxies" - If our universe was "very chaotic place in its infancy" how could it be that we have got immidiatly disk galaxies with massive, bright, star-forming clumps and little regular structure."
Why those massive disc galaxies had been developed in the chaotic Universe? How long it should take to set the first massive disc galaxy in that unclear process? How could it be that all the billions spiral galaxies had been formed from this chaotic Universe?

"Gradually, the galaxies that were to become spirals lost most of their big clumps, and a central, bright bulge would appear; the smaller clumps throughout the galaxy would begin to form indistinct, "woolly" spiral arms.
These arms would only become very distinct arms once the universe was about 3.6 billion years old. At that age, as the galaxies had a chance to settle down, the turbulence decreased, and new stars would form in a much quieter disk. "We can see the transition from the early chaotic state to the modern, relaxed state," said Bruce Elmegreen.
These first spiral galaxies were either two-armed structures or had thick, irregular spirals with some remaining clumps. More finely structured, multi-armed galaxies like the Milky Way galaxy and its neighbor Andromeda appeared much later, when the universe was 8 billion years old."

Second contradiction - "Age" - We see spiral galaxies at the most far end of the Universe.
The estimated age of many mature spiral galaxies is more than 13.2 Billion years.
So, how could we see today very mature spiral galaxies at estimated age of only 0.6 billion years, if based on this article we need several billions (3.6 Min) and also with the assumption that we have got "Massive disc galaxies" almost immediately from the chaotic Universe?

Third contradiction – "Random process" - They don't show exactly how do we get this spiral arms from  massive disc galaxy. They just say that "Gradually, the galaxies that were to become spirals lost most of their big clumps,.."
This is a random activity by definition. They don't say why they lost the big clumps and how they really got their spiral arms based on Newton gravity.

Conclusions:
I have set a simple explanation why 400 Billion spiral galaxies have got their spiral shape from day one based on Newton gravity force.
Our scientists (even at 2014) try to find an explanation which is not correlated to the universe age time frame. This random activity can't be the base for all the billions spiral galaxies that we see in our universe.
I have set my explanations about the spiral arms structures which is much more relaibale from the last "story" from our scientists.

[Halc]

If you agree with that, than this is all is needed to explain the spiral arm structure.

It is far more complicated than either of us can explain.  You have a bowl of cake batter with a bar of dark batter across the middle.  You stir once or twice and you get a spiral structure something like the galaxy.  You stir 40 times and that structure fades to either super-thing spirals or just one color.  How are the arms still there after 40 laps with all the parts moving at different angular speeds around the galaxy?  Our own arm seems to be one of the ones that is being thinned to the point of nonexistence, possibly explaining why we've not been disturbed by the material in a thicker arm which would have disrupted life formation.

As I have stated, each star is connected in the arm by Newton gravity force.
All the stars have a similar orbital speed. (More or less)

Too much speed, but yes, more or less the same.  Not the same angular speed, which would be needed to keep the arms intact indefinitely, but just similar linear speed.

Therefore, for any time frame, they all cross the same distance.

Exactly, but the stars close to the center of the galaxy have far less distance to go, so they go around far more often than the stars at the far ends of the arms that might yet to have gone around even 10 times since they have so much further to travel to achieve one lap.

In order to achieve it, as they drift outwards, they also drift backwards.
That activity sets by definition the spiral shape of the arms.

That drifting outwards and back defines the clumping of the arms.  The spinning at different angular velocities of each end defines the spiral shape, just like the cake batter.

The speed at which everything moves is unexplained by your assertions.  You never address this issue.

Now, let's try to find what our scientists have to say about: "How Our Milky Way Galaxy Got Its Spiral Arms"

Your last link was hardly to a scientist.  This one here is at least a magazine article which presumably has some standards beyond what quora obviously has.

https://www.space.com/24642-spiral-galaxies-milky-way-shape-explained.html
Dated - February 12, 2014

I like this one, reporting on doing the research the correct way:  Look into the past as see how the shapes evolved.  It's sort of like watching an animation of our own galaxy over billions of years, except all the frames have been dropped on the floor and need sorting.
The article is more about how the research was done than what the results of that research were.

"The researchers found that the universe was a very chaotic place in its infancy. The first galaxies were disks with massive, bright, star-forming clumps and little regular structure. To develop the nice spiral forms seen today, galaxies first had to settle down, or "cool," from the previous chaotic phase. This evolution took several billion years."

First contradiction - "Massive disc galaxies" - If our universe was "very chaotic place in its infancy" how could it be that we have got immidiatly disk galaxies with massive, bright, star-forming clumps and little regular structure."
Why those massive disc galaxies had been developed in the chaotic Universe? How long it should take to set the first massive disc galaxy in that unclear process? How could it be that all the billions spiral galaxies formed from this chaotic Universe?

Hard to parse your comments here.  You're suggesting a contradiction, but I don't see one identified.  Higher density matter tends to group due to its mutual attraction.  That forms galaxies.  If the matter has any angular momentum, then the clump will naturally form a disk shape, just like what happens with new solar systems forming out of a gas cloud.  The disk shape is the only way to preserve angular momentum of a compressing structure.

Second contradiction - "Age" - We see spiral galaxies at the most far end of the Universe.
The estimated age of many mature spiral galaxies is more than 13.2 Billion years.
So, how could we see today very mature spiral galaxies at estimated age of only 0.6 billion years, if based on this article we need several billions (3.6 Min) and also with the assumption that we have got "Massive disc galaxies" almost immediately from the chaotic Universe?

Nothing said that very mature spiral galaxies were of age 0.6 billion years.  That would be a young galaxy still lacking a mature spiral structure.  From where are you getting this claim of a spiral galaxy that is only 0.6 BY old?

Third contradiction – "Random process" - They don't show exactly how do we get this spiral arms from  massive disc galaxy. They just say that "Gradually, the galaxies that were to become spirals lost most of their big clumps,.."
This is a random activity by definition. They don't say why they lost the big clumps and how they really got their spiral arms based on Newton gravity.

Missing details is not a contradiction, just not a full description.  Such details might not be clear.  They only looked closely at about 41 galaxies to get an idea of the various stages of the process.  Nobody has a video of the evolution of any one galaxy as it goes through the process.

Conclusions:
I have set a simple explanation why 400 Billion spiral galaxies have got their spiral shape from day one based on Newton gravity force.

You have no such thing.  You just assert it, and the data from the Hubble image clearly shows that assertion to be wrong since no young galaxy has arms, and thus they're not there from 'day one'.

The article you link suggests no explanations whatsoever.  It just reports data: This is what apparently happens.  Given that, find a theory that explains it, but no such theory seems to be proposed in that article.  You have asserted having an explanation, but none is provided.  You just assert the current observed picture, and fail to explain simple observed speeds of the arms.  So your explanation falls completely short of the current views on galaxy dynamics, which are admittedly only best models at the time.  Those models are always changing, especially since none of them really provides a full explanation.

You can accept it or reject it.

And so I have.

[Dave Lev (OP)]

The speed at which everything moves is unexplained by your assertions.  You never address this issue.

Yes, I can explain it.
However, I need to see the real data.

Please look at the "Observed rotation curve" in the following article?
http://ircamera.as.arizona.edu/astr_250/Lectures/Lecture_22.htm
Observed rotation curve:
We see that at about 0.2 KPC the orbital velocity is maximal - 260 Km/sec
Than it goes down to about 190 Km/sec at 3KPC.
From this point it goes up to 210 Km/sec at 4KPC
and to 230 Km/sec at 7 KPC.
Than it starts to go down again to 200 Km/sec at 10KPC
Goes up to 235 Km/sec at 13 KPC and stay at that velocity at any further distance.
Is this correct?

If so, how could it be that we don't see the real orbital velocity near the SMBH?
We know that the orbital velocity of the plasma is 0.3 c (speed of light)
At the end of this article it is stated:
"Consider a star whose proper motion has been measured to be equivalent to 1000 Km/sec and which lies only 0.01 pc from SgrA*.
So, why we don't see the real velocity at the center?\
Why it shows that the orbital velocity at the center is almost Zero?

Why they also give this information without any connection to the galaxy shape?
I would expect to see measured velocities per radius in the following segments:
1. Accretion disc (What is the Min radius and maximal radius. What is the orbital velocity at each radius?
2. Bulge - Radius range and velocities
3. Bar - Radius range and velocities
4. Ring - Radius range and velocities
5. Disc/spiral arms - Radius range and velocities
6. From the end of the disc - Radius and velocities
Would you kindly direct me to the real measurements of orbital velocities Vs radius in the Milky Way? (From 0 - 20K Pc)
I will give full explanation once I have the real data.

[Halc]

The speed at which everything moves is unexplained by your assertions.  You never address this issue.

Yes, I can explain it.
However, I need to see the real data.

Please look at the "Observed rotation curve" in the following article?
http://ircamera.as.arizona.edu/astr_250/Lectures/Lecture_22.htm
Observed rotation curve:
We see that at about 0.2 KPC the orbital velocity is maximal - 260 Km/sec

I get that at about 0.5 KPC.  The linear line to the left of that is consistent with the 'bar' which seems to turn as a solid object instead of a fluid collection of stars and such.  I don't know the current thinking behind what holds a bar together.  A lot of galaxies seem to have one.

Than it goes down to about 190 Km/sec at 3KPC.
From this point it goes up to 210 Km/sec at 4KPC
and to 230 Km/sec at 7 KPC.
Than it starts to go down again to 200 Km/sec at 10KPC
Goes up to 235 Km/sec at 13 KPC and stay at that velocity at any further distance.
Is this correct?

That what it shows, yes.  The 235 is fairly constant out to where most of the measurable material stops, which is about 17 KPC.  It has to drop to a Keplerian curve eventually, else the whole universe would be orbiting our galaxy.

If so, how could it be that we don't see the real orbital velocity near the SMBH?

The graph stops short of that radius.  We know that S2 has speeds up to 5000 km/sec, and that is not in any way reflected in the graph.  S2 is not part of the bar.

We know that the orbital velocity of the plasma is 0.3 c (speed of light)
At the end of this article it is stated:
"Consider a star whose proper motion has been measured to be equivalent to 1000 Km/sec and which lies only 0.01 pc from SgrA*.
So, why we don't see the real velocity at the center?\
Why it shows that the orbital velocity at the center is almost Zero?

It doesn't show velocity close to the center.  The graph stops short of radius 150 PC.  Stuff close in moves fast, as you note above with this 1000 km/sec star being considered.
The graph also doesn't show anything at zero speed.  The bottom of the graph is 150 km/sec, not zero.

Why they also give this information without any connection to the galaxy shape?

It seems there is little connection.  Objects at radius X move at the same speed regardless of being in an arm, near one side or the other, or between them.  The arm might affect regular wobble in and out, but not the tangential speed around the galaxy.

I would expect to see measured velocities per radius in the following segments:
1. Accretion disc (What is the Min radius and maximal radius. What is the orbital velocity at each radius?

The graph actually shows exactly that.

2. Bulge - Radius range and velocities

I suspect this is not uniform since objects have random and probably highly elliptical orbits.  Things at a given distance will have all sorts of different speeds.

3. Bar - Radius range and velocities

The graph seems to show this as well, which is the steep part to the left of the highest point on the curve.  The ends of the bar are moving faster than anything else, just like the ends of the thrown spanner are moving faster than the rest of it.

4. Ring - Radius range and velocities

Graph would need to be extended to the right for this, but there is not a lot of visible material via which distance and speed can be determined.

5. Disc/spiral arms - Radius range and velocities

How is this not number 1 above?

6. From the end of the disc - Radius and velocities

No idea what you mean by this one.

Would you kindly direct me to the real measurements of orbital velocities Vs radius in the Milky Way? (From 0 - 20K Pc)
I will give full explanation once I have the real data.

Your link above seems to be fairly in line with similar graphs I've seen.  If you don't consider that the real data, then nothing I provide will motivate you.  How can you claim to have an explanation if it is based on data that you don't know?  Is there any part of it that is not complete fiction then?

[Dave Lev (OP)]

Thanks

Your link above seems to be fairly in line with similar graphs I've seen.

So as you agree on this graph, let's set the correlation with the structure.
In order to do so, please look at the following diagram of the Milky way structure:
http://www1.ynao.ac.cn/~jinhuahe/know_base/astro_objects/galaxies/Milky-Way-Galaxy-files/logarithmic-spiral-pattern-before2001.JPG
We can see clearly that the radius of the ring is 3Kpc.
Now, please remember that the minimal orbital velocity was exactly at that radius.

Than it goes down to about 190 Km/sec at 3KPC.

So, the orbital velocity at the ring is 190 Kpc.
That shows that at the end of the bar, the orbital velocity is minimal. That evidence contradicts your following message:

The ends of the bar are moving faster than anything else, just like the ends of the thrown spanner are moving faster than the rest of it.

So, the end of the bar has the minimal orbital velocity.
This by itself must set a big red light. How could it be???
In any case, the spiral arms starts exactly at that ring (3KPC).
We don't see the end of the arms but we can assume that it ends at about 15 KPC (at about 45K light year).
Let's focus on the Bar and the bulge:
As we move inwards from the ring the orbital velocity is increasing.
It almost goes to 260 Km/s at 0.5KPC.

I get that at about 0.5 KPC.

However, as we get closer to the center from that radius, the orbital velocity gets down.
At about 0.1 KPC the orbital velocity is almost Zero!!!
This is a very important segment in the galaxy.
There is a meaning for that activity.
Our scientists focus only on the orbital velocity of the stars in the arms, while they ignore completely other important segments..
That shows that their knowledge in spiral galaxy is very poor.
I can explain each segment.
However, do you agree by now that there is high correlation between the galaxy structure and the orbital velocity?
Do you agree that your following message is incorrect?

Why they also give this information without any connection to the galaxy shape?

It seems there is little connection.  Objects at radius X move at the same speed regardless of being in an arm, near one side or the other, or between them.  The arm might affect regular wobble in and out, but not the tangential speed around the galaxy.

[Halc]

So as you agree on this graph, let's set the correlation with the structure.
In order to do so, please look at the following diagram of the Milky way structure:
http://www1.ynao.ac.cn/~jinhuahe/know_base/astro_objects/galaxies/Milky-Way-Galaxy-files/logarithmic-spiral-pattern-before2001.JPG
We can see clearly that the radius of the ring is 3Kpc.

There is no ring depicted there.  There are some dots that are part of the polar coordinates graph, but no physical ring.  The ring I think is way outside, like maybe 40 kps or something, a halo of gas not particularly dense enough to form luminous objects.

So, the orbital velocity at the ring is 190 Kpc.

The speed of the ends of the bar.  No ring there.  Yes, the bar is larger than I posted before, and the curve would not make sense for an object that retains its shape like that.  Are the stars being measured not part of the bar?  What comprises the bar then?  I said I've not seen a description of how that supposedly works.  The site is not much help.  Hard to read the text that goes along with your picture.

That shows that at the end of the bar, the orbital velocity is minimal. That evidence contradicts your following message:

The ends of the bar are moving faster than anything else, just like the ends of the thrown spanner are moving faster than the rest of it.

Yes, clearly the part of the curve I identified with that sort of motion is not the bar, or not all of it.

So, the end of the bar has the minimal orbital velocity.
This by itself must set a big red light. How could it be???

Good question.  I don't know the answer to that one.  There must be some website that explains how that works, and what was being measured on that curve.

In any case, the spiral arms starts exactly at that ring (3KPC).
We don't see the end of the arms but we can assume that it ends at about 15 KPC (at about 45K light year).
Let's focus on the Bar and the bulge:
As we move inwards from the ring the orbital velocity is increasing.
It almost goes to 260 Km/s at 0.5KPC.
However, as we get closer to the center from that radius, the orbital velocity gets down.
At about 0.1 KPC the orbital velocity is almost Zero!!!

Nothing shows that.  The min speed is 150 km/s at that radius where the graph ends.  Here's a more detailed version of the same graph, from the same site as your link above:
http://www1.ynao.ac.cn/~jinhuahe/know_base/astro_objects/galaxies/Milky-Way-Galaxy-files/rotation-curve-10kpc.PNG
That one shows the data points that make up the curve.  The data points follow the curve quite well up to about 8.5 kps, after which there are many points significantly above and below.  The curve is flat to the right because the data points are so imprecise and so few that fitting a better curve is meaningless.  On the left, I see no object slower than 200 km/sec, but the line continues the apparent trend.  All very non-Keplerian.

This is a very important segment in the galaxy.
There is a meaning for that activity.
Our scientists focus only on the orbital velocity of the stars in the arms, while they ignore completely other important segments..
That shows that their knowledge in spiral galaxy is very poor.

No, it means that not a lot of pop-science web sites focus on that part.  I haven't tried much to actually see what the consensus is about how things move in that inner 3 kps, and how the bar keeps its shape.  Such a thing is fairly common, hardly a weird anomaly of just our own galaxy.

I can explain each segment.
However, do you agree by now that there is high correlation between the galaxy structure and the orbital velocity?

Well I don't see it from that data.  The bar suggests one curve, and the graph shows another.  That's pretty louse correlation.  The rest of the curve (outside 3kps) doesn't have a curve that changes say in a pattern that matches the spacing of the arms, so again, little correlation. 

Do you agree that your following message is incorrect?

It seems there is little connection.  Objects at radius X move at the same speed regardless of being in an arm, near one side or the other, or between them.  The arm might affect regular wobble in and out, but not the tangential speed around the galaxy.

I think something definitely changes around 3kps, but other than that, I stand by my comment above.  I see little correlation between structure and the shape of that curve.

[Halc]

Another nice picture from the same site shows the arm structure better:
http://www1.ynao.ac.cn/~jinhuahe/know_base/astro_objects/galaxies/Milky-Way-Galaxy-files/MW-spirals-annotated.jpg

The arms seem not to be continuous tubes of stellar material, but rather chunks arranged sort of like fallen dominoes.  It seems like the dominoes separate as the different path lengths pull them apart, and they rejoin elsewhere, thus never letting the arms thin out to nothing.  Our own particular domino has separated in this manner, more than most of them.  It is probably headed for the more dense Perseus arm to the outside.  Just my guess.

The arms form a more elliptical shape near the bar, not a nice near circular spiral like all the diagrams show.
This is not a photo of course, just an artist's rendering.

[Dave Lev (OP)]

No, it means that not a lot of pop-science web sites focus on that part.  I haven't tried much to actually see what the consensus is about how things move in that inner 3 kps, and how the bar keeps its shape.  Such a thing is fairly common, hardly a weird anomaly of just our own galaxy.

Please look at the following image from NASA (which is identical to the one that you have offered)
https://solarsystem.nasa.gov/resources/285/the-milky-way-galaxy/
It shows clearly that at 3KPC there are two sides of the ring
The one which is closer to the Sun is called: Near 3KPC Arm
The one which is farther from the Sun is called: Far 3KPC Arm
Together they set the ring.
The end of the Bar is directly located just between those arms on each side.
How can you claim that:

The arms seem not to be continuous tubes of stellar material, but rather chunks arranged sort of like fallen dominoes...

Well I don't see it from that data.

The ring I think is way outside, like maybe 40 kps or something, a halo of gas not particularly dense enough to form luminous objects.

The data is clear. It is time for you to agree with the evidences.
There is a clear ring at 3KPC!!!
This ring has a great impact on the activity of the galaxy.
I will explain it later on.
But first - do you agree that :
1. There is a ring at 3KPC?
2. The orbital velocity at that ring is minimal - 190 Km Sec?
3. The Bar ends exactly at that ring?
4.The arms starts to form exactly from that Ring?
Why do you disqualify even the clear evidences which me & you represent?
Why are you so negative?
Would you kindly look again at the evidences and try to understand that spiral galaxy is not just spiral arms?
Would you kindly try to be more cooperative and help us to highlight the real activity at spiral galaxy?

[Halc]

Please look at the following image from NASA (which is identical to the one that you have offered)
https://solarsystem.nasa.gov/resources/285/the-milky-way-galaxy/
It shows clearly that at 3KPC there are two sides of the ring

That's the same image (different link) as in my prior post.
There is no ring identified or depicted.  I see the inner ends of what are the Perseus and Scutum-Centarurus (or Crux-Scutum) arms, but they're called Near and Far 3kpc arm that far in.  There is no ring there.

The one which is closer to the Sun is called: Near 3KPC Arm
The one which is farther from the Sun is called: Far 3KPC Arm
Together they set the ring.

No, they set the inner portions of a spiral.
If you want to call it a ring, fine, but the two arms do not connect.  Each spirals out into the two major arms.  The image clearly shows this.  I notice both arms get noticeably thicker at the point halfway around when the pass relatively close by the opposite end of the bar from which they appear anchored.

The end of the Bar is directly located just between those arms on each side.

Yes, each major arm is anchored on one end of the bar.  Your prior wiki image shows it in more graphic form:
https://en.wikipedia.org/wiki/Milky_Way#/media/File:Milky_Way_Arms.svg
That image has the sun on top instead of the bottom.  It shows for instance the aqua Perseus arm just outside our position going a full lap around the galaxy where it becomes named the <near> 3kpc arm before it 'connects' to the bar.  That image fails to name the far 3kpc arm that is the bright green line.

How can you claim that:

The arms seem not to be continuous tubes of stellar material, but rather chunks arranged sort of like fallen dominoes...

Because that's what I see in the picture you just linked.

The data is clear. It is time for you to agree with the evidences.
There is a clear ring at 3KPC!!!
This ring has a great impact on the activity of the galaxy.
I will explain it later on.

No site calls that a ring.  If you want to, fine. It seems to be important to you.

But first - do you agree that :
1. There is a ring at 3KPC?

No.  It is the inner ends of the two major arms: a pair of spirals.
If you want to consider those portions not part of their arms, but a ring instead, I will entertain your idea if it actually demonstrates something.

2. The orbital velocity at that ring is minimal - 190 Km Sec?

According to that rotation curve, it seems so, yes.  But without explanation of the bar, I'm not sure what is being measured by that rotation curve because the bar could not be stable given that curve.

3. The Bar ends exactly at that ring?

It seems to end where each spiral starts, yes.  The opposite end of say the near 3kps arm is outside the bar and does not connect to the far 3kps arm that starts there.

4.The arms starts to form exactly from that Ring?

They start from the bar.  The 3kps arms are the two major arms of the galaxy.  Sorry, but it seems I don't agree to much of what you see.

Why do you disqualify even the clear evidences which me & you represent?
Why are you so negative?

You seem to need a situation to be what it isn't.  For instance you deny tidal forces because your agenda needs to have the moon drifting away naturally, without forces acting on it.  You are bending data at every step to fit a broken model instead of finding a model that fits the data.  It is a really bad way to go about learning.  It is a method of obfuscation.
You demonstrate not even minimal awareness of orbital mechanics, and yet you claim to have a theory that is better than the ones presented by people who know their stuff better than any of us.  Of course I'm going to resist what are very apparent attempts to bend observed data.

Would you kindly look again at the evidences and try to understand that spiral galaxy is not just spiral arms?
Would you kindly try to be more cooperative and help us to highlight the real activity at spiral galaxy?

Like I said, you can present the inner portions of the arms as one ring if you like since they're not too distant from each other.  Not sure what your point is in doing that, but it isn't a major bending of what that picture shows.  I'd like to hear your point.
As you say, that curve does not fit a picture with a bar in it.  The curve seems very inconsistent with what appears to be the shape of a common galactic feature.  There is something going on that neither of us understands, so I'm not exactly claiming myself to have a better understanding of the dynamics of a galaxy.

I'd like to see an animated gif or something of a spinning galaxy.  If it had all the parts moving consistently with that rotation curve, the thing would smear out in a short time.

I found this nasa one:
https://gizmodo.com/5953694/this-stunning-nasa-simulation-shows-a-galaxys-entire-life-history
That's a really fast simulation at ~100 million years per second or so, so it is hard to see how the arms continuously merge and reform.  The bar is hard to make out near the end, but in the middle it seems to rotate the opposite way as everything else.  The roatation curve then would be the speed of all the stuff flying loose around, but not of the bar itself.  That might be one answer to that seeming inconsistency.

Most of the simulations are of long lifespans.  I wanted something a little more slow motion.  The bar seems to spin so fast that it might be the frame rate that makes it look like its going backwards.

I can find no decent simulation of a nice slow picture of say 200 million years compressed into a minute or two.  They're all much faster, making the interactions go by too fast to answer the sorts of questions we're asking here.

[Dave Lev (OP)]

The one which is closer to the Sun is called: Near 3KPC Arm
The one which is farther from the Sun is called: Far 3KPC Arm
Together they set the ring.

No, they set the inner portions of a spiral.
If you want to call it a ring, fine, but the two arms do not connect.  Each spirals out into the two major arms.  The image clearly shows this.  I notice both arms get noticeably thicker at the point halfway around when the pass relatively close by the opposite end of the bar from which they appear anchored.

No - None of them spirals out. Our scientists call them 3KPC as they stay at 3KPC.
Yes - They are connected at their edges to other spiral arms, but they together set a ring or almost a ring.
I hope that the following image can give you better overview
https://crossfithartford.com/dummies_diagram_of_plant_the_milky_way.php
We can see the two 3KPC arms.
One is called near 3KPC arm and the other Far 3KPC arm.
Why do we call them both 3KPC arm?
Don't you think that the name of the 3KPC represents their radius???
It also seems that both of them are connected/almost connected.
In the following image it is quite clear:
https://solarsystem.nasa.gov/resources/285/the-milky-way-galaxy/
We see that in one side they are connected at a point which is written as galactic bar, while on the other side it is called long bar. At those points we also see the connections to the main spiral arms.
In the image it looks like elliptic ring shape.
However, don't you agree that the mane - 3KPC arm proves that this arm is located all the way at a radius of 3KPC?
They both stay there by themselves.  None of them is part of another spiral arm.
Therefore, if one arm covers the upper half/almost half of the cycle, while the other arm covers the other half/almost half of the cycle, don't you agree that in the total we get a ring/almost ring
You might call it as upper 3KPC arm + lower 3KPC arm.
However, even if you don't see a perfect ring, it is still a ring (or almost a ring...)
We know that the orbital velocity goes down to its minimal value exactly at 3KPC.
Therefore, this ring is a key element in the activity of the galaxy.