[Bored chemist]

They see a star in the spiral arm and they think that it should hold itself by its own gravity to the center of the galaxy.
In other words - they totally ignore the impact of the arm.

Please provide evidence that they think that , or anything like it.

[Origin]

Do you reconfirm that in a solid arm "the one that is twice as far out has to travel twice as far to complete one orbit."
Yes or No, please?
Do you confirm the Bar arm meets your calculation for solid arm?
So, as the Bar arm looks solid, Behave solid & meets you calculation for solid arm by 100%  - then why do you claim that it can't be solid?
Are you sure that only astrophysicist can approve this observation?

It is difficult to have a science related discussion with someone who does not even know what a solid is.

Hence, if that astrophysicist would tell you that the Bar arm is solid as it fully meets the calculation for solid arm - would you believe him?

Of course not.

[Kryptid]

Do you reconfirm that in a solid arm "the one that is twice as far out has to travel twice as far to complete one orbit."
Yes or No, please?
Do you confirm the Bar arm meets your calculation for solid arm?

Yes, but that isn't the only requirement for something to be solid: https://en.wikipedia.org/wiki/Solid

So, as the Bar arm looks solid, Behave solid & meets you calculation for solid arm by 100%  - then why do you claim that it can't be solid?

Because it's mostly made of gas.

Are you sure that only astrophysicist can approve this observation?

An astrophysicist would know that it's mostly gas.

Hence, if that astrophysicist would tell you that the Bar arm is solid as it fully meets the calculation for solid arm - would you believe him?

I'd question his merits as an astrophysicist, as it is, again, mostly gas.

So where can we find that astrophysicist?

I have no idea where you'd find an astrophysicist who would state that something made mostly of gas is solid.

One more question;
If one day as you go out from your home, you observe something that looks like a lion.
It  has a body of a lion, a head of a lion a voice of a lion a smell of a lion and it run and jump as a lion directly to your location.
What would you do?
1. As you had been informed by the experts that there are no lions in your city,  you would assume that it is just a swarm of flies that only looks like a lion. Therefore you would stay where you are and hope that those flies would escape from this lion structure.
2. Call the expert (this time it can't be astrophysicist) to get his advice if this structure represents real lion.
3. Run for your life.
Please take your time. You still have few more second before the impact.

This is a ridiculous analogy. Galactic structures don't "look" solid. Again, they are mostly gas and we know this.

[Dave Lev (OP)]

Quote from: Dave Lev on Today at 09:56:49
Do you reconfirm that in a solid arm "the one that is twice as far out has to travel twice as far to complete one orbit."
Yes or No, please?
Do you confirm the Bar arm meets your calculation for solid arm?

Yes, but that isn't the only requirement for something to be solid: https://en.wikipedia.org/wiki/Solid

Thanks for your honest answer.
So, based on the orbital velocity of the stars in the bar arm, you fully confirm that the stars there meets your calculation for solid arm.
This is very important confirmation and I would like to thank you for that!

However, I called the bar "solid" but you don't like that name.
So let me ask you differently:
If the bar behave as a stable structure (not solid) and it looks like a stable structure (bar everywhere) - then why it can't be considered as stable structure?

You claim that it is due to the gas:

Galactic structures don't "look" solid. Again, they are mostly gas and we know this.

Let's verify the issue with the gas:
Do you agree that our sun is made out of gas (mainly: Hydrogen & helium)
So does it mean that the Sun has no gravity force?
What's wrong with gas that is concentrated in a star?
Don't you agree that this gas star that is called Sun can hold all the planets and moons around it for billions of years by simple gravity force?
So, what's wrong with the gravity force of gas or gas stars?
Do you think that once a star gets into the bar its gravity force is cancelled?
What is the problem that prevents from the gas stars to form a stable bar structure that holds itself by mutual gravitational attraction?

Please look at the following image of M80:
https://en.wikipedia.org/wiki/Globular_cluster#/media/File:A_Swarm_of_Ancient_Stars_-_GPN-2000-000930.jpg
"M80 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction."
Why do you give a permission to those hundreds of thousands of stars to held together by their mutual gravitational attraction, but you prevent from the same "mutual gravitational attraction" to work at the bar?

[Origin]

Thanks for your honest answer.
So, based on the orbital velocity of the stars in the bar arm, you fully confirm that the stars there meets your calculation for solid arm.

Its ironic that you say thanks for the honesty and then immediately dishonesty imply that kriptid agreed with your silly conjecture.

However, I called the bar "solid" but you don't like that name.

Since that is wrong it is not surprising.

If the bar behave as a stable structure

It doesn't.

[Kryptid]

Why are you arguing about this "bar" thing anyway? It already follows the predicted Keplerian curve on the graph. I don't know what you think is a mystery about it.

[Dave Lev (OP)]

Why are you arguing about this "bar" thing anyway? It already follows the predicted Keplerian curve on the graph

The bar is a key element in the spiral galaxy.
Don't you agree that It follows the predicted Keplerian curve on the graph for a stable bar structure?
However, in this case, I can claim that there is no need for dark matter to explain the Bar orbital velocity.
That could kill the idea of the dark matter.
So, you all reject this clear observation in order to keep the dark matter imagination.

However, you can't escape from the reality
1. The bar looks stable
2. The orbital calculation proves that the Bar behaves as a stable structure
Therefore it must be stable structure and there is no need for dark matter to explain the orbital velocity at the Bar.

I don't know what you think is a mystery about it.

The mystery is that you are not willing to accept the meaning of the orbital velocity at the bar.
Why do you insist to ignore the observation and orbital calculation of the Bar?
Are you really afraid that there will be no need for dark matter at the Bar?

If this bar was made out of Iron, would you accept the idea that it is stable?
So, can we agree that based on the orbital calculation it should be stable.
But, you don't accept the calculation as the bar is made out of stars and based on your understanding stars can't be hold together by their mutual gravitational attraction as they are made out of gas.
Correct?

[Kryptid]

However, in this case, I can claim that there is no need for dark matter to explain the Bar orbital velocity.
That could kill the idea of the dark matter.

No, because it's needed for the outer regions of the galaxy.

Therefore it must be stable structure and there is no need for dark matter to explain the orbital velocity at the Bar.

I never said that dark matter was needed for the bar.

The mystery is that you are not willing to accept the meaning of the orbital velocity at the bar.
Why do you insist to ignore the observation and orbital calculation of the Bar?

Who said I was?

Are you really afraid that there will be no need for dark matter at the Bar?

Nope.

If this bar was made out of Iron, would you accept the idea that it is stable?

If it was made out of iron, its properties would be entirely different than they are now.

But, you don't accept the calculation as the bar is made out of stars and based on your understanding stars can't be hold together by their mutual gravitational attraction as they are made out of gas.
Correct?

Metastable is probably the better word.

[Dave Lev (OP)]

Quote from: Dave Lev on Today at 20:12:19
Therefore it must be stable structure and there is no need for dark matter to explain the orbital velocity at the Bar.

I never said that dark matter was needed for the bar.

Thanks
So can we agree that the dark matter is not needed for the bar, but you think that it is needed for the spiral arms?

[Kryptid]

but you think that it is needed for the spiral arms?

Yes.

[Bored chemist]

The bar is a key element in the spiral galaxy.

Yes.
But it isn't solid.

The bar looks stable

So does a picture of a swarm of bees

[Dave Lev (OP)]

but you think that it is needed for the spiral arms?

Yes.

Thanks
So, you think that the dark matter is needed for the spiral arms.
We will discuss latter on about the spiral arms.
However, I hope that by now you fully confirm that there is no need for dark matter in the bar as all the hundreds of thousands/millions of stars there are bonded together in that Bar shape by their mutual gravitational attraction.

Quote from: Dave Lev on Yesterday at 20:12:19
The bar looks stable

So does a picture of a swarm of bees

Well, in a swarm of bees they are bonded together by their common wish to stay together.
Stars have no wish.
They are bonded together by their mutual gravitational attraction
We already know how the Globular_cluster that is called M80 works:

Please look at the following image of M80:
https://en.wikipedia.org/wiki/Globular_cluster#/media/File:A_Swarm_of_Ancient_Stars_-_GPN-2000-000930.jpg
"M80 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction."

Each star in this Globular_cluster orbits around its common center of mass that had been set by the mutual gravitational attraction of all the other stars in that cluster.
This is the formula for the Com of collection of particles/orbital objects/stars
http://hyperphysics.phy-astr.gsu.edu/hbase/cm.html
As the cluster has a spherical shape, there is a possibility that all the stars orbits around the same Com.
However, the Bar has a different shape. It looks like a long arm.
Therefore, in this case, while each star in the bar orbits around its unique Com, those Coms are bonded together by the mutual gravitational attraction.
Hence, while each star orbits around its Com, the bar arm is so stable.
Therefore, I agree with you that the stars in the bar looks like swarm of bees, however, while the bees stay together by their common wish, the stars stay together by their common center of mass due to the mutual gravitational attraction.
Is it clear?

[Dave Lev (OP)]

In the following article it is stated:
https://news.berkeley.edu/2017/06/13/new-evidence-that-all-stars-are-born-in-pairs/
New evidence that all stars are born in pairs.
"The new assertion is based on a radio survey of a giant molecular cloud filled with recently formed stars in the constellation Perseus, and a mathematical model that can explain the Perseus observations only if all sunlike stars are born with a companion."
The Sun also might have a companion but it had not been found yet:
"Astronomers have even searched for a companion to our sun, a star dubbed Nemesis because it was supposed to have kicked an asteroid into Earth’s orbit that collided with our planet and exterminated the dinosaurs. It has never been found."
In this case, it is expected that stars with companion would orbit around their Common center of mass and that Com would be bonded to the arm by the mutual gravitational attraction from all the star in the arm.
There is a possibility that Nemesis is some sort of dark star or just a BH that we can't see.
If it is real, Nemesis is responsible for the wobbling motion of the Sun as they both orbit around their mutual Common center of mass while bond themselves in the Orion arm by the mutual gravitational attraction with all the other stars in the arm.
Please look at the motion of the solar system in the galaxy.
https://www.pinterest.es/pin/452752568775036247/
It looks almost identical to the Moon motion around the Sun.

[Dave Lev (OP)]

Please look at the following motion of the stars in the local solar neighborhood in the Orion arm
https://bhavanajagat.files.wordpress.com/2014/09/whole-cookie-whole-revolution-rotation-of-galaxy.png
Each star is moving in other direction.
Based on this image you might think that all of them would shortly move away from each other.
However, that isn't the case.
If I remember correctly the relative motion of those stars is in the range of about 20Km/s.
Hence, each star in this local solar neighborhood orbits around its Com at about that velocity, while they all are bonded by the mutual gravitational attraction with all the other stars in the arm and they orbit around the galaxy at about 220Km/s.
Therefore, they behave as swarms of bees but instead of just common wish to stay together, they share a gravitational attraction that force them to stay together.

[Bored chemist]

Well, in a swarm of bees they are bonded together by their common wish to stay together.

Which would make them more like a liquid than a solid, wouldn't it?
A liquid has no fixed shape, and nor does a swarm.

So will you please stop trying to say that a galaxy (or any part of it bigger than a planet) is solid.
It just isn't.

[Bored chemist]

Therefore, they behave as swarms of bees but instead of just common wish to stay together, they share a gravitational attraction that force them to stay together.

And a swarm of bees is not a solid, is it?

[Dave Lev (OP)]

Well, in a swarm of bees they are bonded together by their common wish to stay together.

Which would make them more like a liquid than a solid, wouldn't it?
A liquid has no fixed shape, and nor does a swarm..

How can you compare a swarm of bees to liquid?
Each bee comes with integrated wings and mind.
It can fly to the left or to the right based on her personal wish.
Therefore, if the bees wish to establish a fixed shape - they can do it.
Liquid has no mind, no wish, no wings and therefore it can't set any fixed structure.
Stars also have no mind, no wish, no wings but they have gravity.
That gravity can bond them in a fixed shape as M80 

Please look at the following image of M80:
https://en.wikipedia.org/wiki/Globular_cluster#/media/File:A_Swarm_of_Ancient_Stars_-_GPN-2000-000930.jpg
"M80 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction."

All the stars there are bonded together by their mutual gravitational attraction and set the fixed shape of the Globular_cluster.
So, how can you claim that this fixed shape of Globular_cluster is just liqued.

One more issue, if you think about liquid, why you didn't use this example at the first stage instead of your imagination about swarm of bees or flies?
Is it just to confuse the other side?

[Origin]

All the stars there are bonded together by their mutual gravitational attraction and set the fixed shape of the Globular_cluster.
So, how can you claim that this fixed shape of Globular_cluster is just liqued.

Of course no one said it is liquid, just more bad faith arguments on your part.  The stars are moving in the globular cluster so the shape is not fixed.

Is it just to confuse the other side?

It seems hard to imagine you could be any more confused

[Dave Lev (OP)]

The stars are moving in the globular cluster so the shape is not fixed.

Globular cluster has a fixed spherical shape. It has a fixed structure although the stars are in orbital motion in that cluster.
If you take a section from the Bar arm or the spiral arm and set it outside the galactic disc, then it would be transformed into that globular cluster.
So all of those globular clusters represent section from the spiral arms which had been disconnected from the arm. (Mainly from the edge of the spiral arm).
The arm works on the same gravity laws as M80.
Therefore, if we could take M80 and replace it back at the bar or at the spiral arm it would get back the arm shape.
Technically, if we could grab by gravity one side of M80 and spin it, you would also get the arm shape.
We will discuss later on how the arms really work.

[Bored chemist]

How can you compare a swarm of bees to liquid?

Because it will flow round an obstacle - unlike a solid.

Therefore, if the bees wish to establish a fixed shape - they can do it.

But they don't. So your "point" is meaningless, isn't it?

Liquid has no mind, no wish, no wings and therefore it can't set any fixed structure.

And the same is true of a galaxy of stars.
You just pointed out that I'm correct to say that they have characteristics in common.

That gravity can bond them in a fixed shape as M80 

It's still not a fixed shape is it?
Why are you pretending it is.


If it was solid, you couldn't fly a ship through it,could you?
If it was solid, the different bits couldn't be moving WRT eachother, could they?

Is it just to confuse the other side?

I don't need to "confuse" the other side if they can't distinguish a gas from a solid.
You are already confused, aren't you?