[Kryptid]

How long do we need to wait?

I don't know, as I haven't looked up the numbers. Given that gravity is about 10⁴⁰ times weaker than electromagnetism, we'd have to wait much, much longer than we would for normal matter to condense.

The age of the Milky Way is estimated for more than 12 BY. So why the dark matter in our galaxy didn't clump yet?

Not enough time has passed yet. Gravitational waves carry away extremely small amounts of energy for all but the most massive objects.

Well, can we claim that as we don't know how the ordinary matter can explain the activity in the spiral galaxy, we have decided that we need some support for extra gravity?

That is what the observations say, yes.

Therefore, can we agree that as we have decided that there is a need something that we can't see, can't smell and can't feel, let's call it dark matter and claim that it can only contribute extra gravity?

That's what the observations suggest, yes.

Did we even found even one particle of dark matter?

Not unambiguously.

Do we really know how the gravity could spread the dark matter particles in the galaxy so it would fit to the requested formula?

What formula are you talking about?

As the dark matter is up to 100,000 LY it is very clear that the solar system and the Earth should constantly collide with dark matter particles as they orbit around the galaxy. So why we can't see a rain of dark matter particles falling on our heads?

Because, as has been stated before, dark matter only seems to interact gravitationally. In order to see something, it has to interact with light in some way. Dark matter is invisible because it doesn't interact with electromagnetism.

If you think that the solar system is not big enough, then what about the spiral arms or ring? The thickness of the ring is 3,000 LY.

That doesn't matter if it only interacts via gravity.

Don't you agree that it is quite massive object that should collide with the dark matter - if there was any dark matter?

No. Dark matter is not tangible. It passes through normal matter as if it wasn't there (similar to neutrinos). That is because it doesn't interact with the electromagnetic force. Normal matter does, that is why normal matter can't pass through other matter in such a ghost-like manner.

If the dark matter can't shed its energy, then why do we ignore its impact?

You mean ignore it physically impacting us? I already answered that above.

As the total mass of the dark matter is at least 5 times bigger than the ordinary matter, why we can't assume that some of the cosmic energy is due to dark matter/energy?

What do you mean by "cosmic energy"?

If the galaxy with its ordinary matter/stars is changing much faster than the dark matter, then then how the dark matter can fit itself to changes in the galaxy?

Who said that it was? It's not like dark matter has to do such a thing.

Do you agree that if in the past the dark matter was OK for the Milky way, then as the galaxy had been surly changed in the last billions years - then the old dark matter density (that can't change fast enough) can't fit anymore to the current milky way?

Over a few billion years, the Milky Way probably hasn't changed a whole lot in terms of its overall shape, honestly.

In other words - why can't we just agree that our scientists have invented the idea of dark matter as they have no clue how spiral galaxy can work only based on ordinary matter?

That's pretty much exactly what dark matter is: a concept invoked to explain anomalies in the observations. That's how a lot of science works.

[Dave Lev (OP)]

That's pretty much exactly what dark matter is: a concept invoked to explain anomalies in the observations. That's how a lot of science works.

In order to understand why our scientists need dark matter let me use the following explanation:

1. Spiral arms can't be a rigid structure as they do not rotate as a solid object:
https://www.forbes.com/sites/jillianscudder/2016/03/22/astroquizzical-spiral-galaxy-arms/?sh=5380839418c5
"spiral arms are still kind of weird. If the galaxy was a static object, like our circle made of paint, and rotated as a unit, you’d need the spiral arms to have been there from the galaxy’s birth, but once they got there you could keep them fairly easily. Unfortunately, we can see that galaxies don’t rotate as a solid object, like a DVD in a player."
In this case, it is expected that the orbital velocity of stars in the edge of the spiral arm would be much faster than the orbital velocity of the one in the base of the arm.
Therefore - our scientists have concluded that the spiral arm isn't a solid object

2. Winding problem
"So that idea’s out; what next? The stars and gas which are closest to the center of a spiral galaxy rotate faster around the center than the stars at the outskirts. This difference in rotation speeds means, if you give a galaxy a spiral arm pattern and then let the galaxy just exist for a little while, your nice loose spiral arm pattern will wind up into a really tight spiral, and the lack of space between arms will make it hard to even spot them in the first place. So if this scenario is the case, then the strong spiral arm features shouldn’t last long. Again, there are problems; if spiral arms shouldn’t last very long, then in general you wouldn’t expect to see many strong spiral arms if you look out at the galaxy population. And while there are certainly galaxies without distinct spiral arms, there are a lot of galaxies with strong spiral features. We'll have to throw out this idea as well."

Let's stop at this point
Now we all know why our scientists have concluded that the spiral arms can't be a solid structure.
However, they do not disqualify the idea that a star can holds itself to the spiral arms by gravity.
They just claim that if the spiral structure was solid, it just can't work - and they are correct by 100%.

Therefore, they have offered two different theories:
- Dark matter- in order to explain the average orbital velocity of each star at any given location in the spiral arm
- Density wave idea in order to explain the spiral stricture:
"What we are left with is an idea called spiral density wave theory, which suggests that the spiral arms aren’t a physical “thing”, but are made of stars which are simply passing through, more like a traffic jam than anything else. "
It is stated very clearly:
" The apparent spiral arms appear because stars don't orbit the center of the galaxy in perfect circles. Each star is instead on an elliptical orbit, much like the recurrent comets in our solar system.  As stars are moving the slowest at the distant edge of their orbit, if a large number of stars have turnaround points around the same place, you'll wind up with an extra dense region of stars, creating an apparent spiral arm. Each star will continue along its own orbit, drifting in and out of spiral arms as the galaxy spins"

Conclusion:
If the solid spiral arm was correct - then we eliminate the need of dark matter, but we end up with winding problem
Therefore, our scientists need two theories - Dark matter and density wave to explain the basic structure of spiral arms
Do you agree with this understanding so far?

[Kryptid]

Density wave theory is not something I am well acquainted with, so I don't know if everything you've said is accurate or not. I know that dark matter is invoked to explain the galactic rotation curve anomaly. I don't know the relationship of that to the nature of the spiral arms.

[Dave Lev (OP)]

Don't you agree that here must be a connection between the dark matter and the winding problem?
If the solid spiral arm was correct - then we eliminate the need of dark matter, but we end up with winding problem
Therefore, our scientists need two theories - Dark matter and density wave to explain the basic structure of spiral arms

[Dave Lev (OP)]

Density wave theory is not something I am well acquainted with, so I don't know if everything you've said is accurate or not.

Dear Krptid
It's not about what I said, it is all about what is stated in the article:
It is stated clearly that they have considered a possibility that the spiral arm is rigid or static object:
https://www.forbes.com/sites/jillianscudder/2016/03/22/astroquizzical-spiral-galaxy-arms/?sh=5380839418c5
"If the galaxy was a static object, like our circle made of paint, and rotated as a unit,"
In this case, all the stars are hold together by gravity.
Therefore, there is no need for Dark matter.
Again, they have disqualified this idea not because they think that gravity can't hold stars in the spiral arms, but because of the winding problem.
Therefore, again - do you confirm that based on this article we can understand that stars can hold themselves in the spiral arms by gravity?

[Dave Lev (OP)]

In order to understand how spiral galaxy really works, we need to understand how each element in the galaxy works.
One of the most important element in the spiral galaxy is the Bar.
Our scientists are using the dark matter to explain the orbital motion of the stars in the spiral arms (and only in the spiral arms) while they totally ignore the other elements especially - the Bar.
However, if they would understand what is the main functionality of this bar they could understand how the spiral galaxy works as one complex organism.
I have just found an excellent article about the Bar:
https://scitechdaily.com/galactic-bar-paradox-a-mysterious-and-long-standing-cosmic-conundrum-resolved-in-cosmic-dance/
It is stated:
"The bar pulsations result from its regular encounters with the Galactic spiral arms, in what can be described as a “cosmic dance”. As the bar and spiral arm approach each other, their mutual attraction due to gravity makes the bar slow down and the spiral speed up.Once connected, the two structures move as one and the bar appears much longer and slower than it actually is. As the dancers split apart, the bar speeds up while the spiral slows back down."
It is specifically stated: "their mutual attraction due to gravity makes the bar slow down and the spiral speed up."
It is also stated: "Once connected, the two structures move as one"

So it is all about gravity that connects the stars in the Bar to those in the spiral arm so they all become one.
Wow!!!
What a great information!!!
I was looking for that information for years.
This is the smoking gun of the spiral galaxy!

Not gravity between dark matter to ordinary matter but gravity between two key elements (Bar and spiral arms) in the spiral galaxy that are all based on ordinary matter as stars.
If our scientists would understand the real meaning of this explanation, they would verify that there is no need for dark matter. The stars (ordinary matter) in each element in the galaxy are good enough to maintain its full structure (Bulge, Bar, Ring, Spiral arms...) without any need for even one particle of dark matter!
Take out one element from that complex and you break down the galaxy.
Nothing would help - not even dark matter.
So, do you accept the idea that in this article they clearly discuss about the impact of real gravity between two key elements in the spiral galaxy (without even one word about the dark matter imagination)?

[Kryptid]

Don't you agree that here must be a connection between the dark matter and the winding problem?

Maybe, I'm not sure.

Therefore, again - do you confirm that based on this article we can understand that stars can hold themselves in the spiral arms by gravity?

Gravity can't hold things together as if they were solid objects, so I hope that's not what you meant by this question.

So, do you accept the idea that in this article they clearly discuss about the impact of real gravity between two key elements in the spiral galaxy (without even one word about the dark matter imagination)?

Even if dark matter isn't necessary to explain the structure of the spiral arms, it is still necessary to explain the anomalous galactic rotation curve (either that or some version of MOND or some other new theory).

[Dave Lev (OP)]

Quote from: Dave Lev on Yesterday at 14:18:22
Therefore, again - do you confirm that based on this article we can understand that stars can hold themselves in the spiral arms by gravity?

Gravity can't hold things together as if they were solid objects, so I hope that's not what you meant by this question.

I hope that the observation is still important for you.
So, please would you kindly read again the following?
https://scitechdaily.com/galactic-bar-paradox-a-mysterious-and-long-standing-cosmic-conundrum-resolved-in-cosmic-dance/
"Once connected, the two structures move as one and the bar appears much longer and slower than it actually is."
What is the meaning of this statement?
Could it be that our scientists observe that the Bar and the spiral arms are connected as one solid object?
If not, then please explain what do you understand from this observation?
If yes, then what kind of force connects the bar and spiral as one solid object?
Let's read the following:
https://scitechdaily.com/galactic-bar-paradox-a-mysterious-and-long-standing-cosmic-conundrum-resolved-in-cosmic-dance/
"As the bar and spiral arm approach each other, their mutual attraction due to gravity makes the bar slow down and the spiral speed up."
What is the meaning of: "their mutual attraction due to gravity makes the bar slow down and the spiral speed up"?
Could it be that when our scientists claim that: "their mutual attraction due to gravity" they don't think about gravity?
So please, based on this explanation, what kind of mutual attraction force holds the bar and the spiral arm as one solid object?
Is it dark matter, dark energy, dark glue or just a simple mutual gravity force?

[Kryptid]

Could it be that our scientists observe that the Bar and the spiral arms are connected as one solid object?

No.

If not, then please explain what do you understand from this observation?

It means that their motions are associated with each other, at least temporarily. To say that two objects bound by gravity is solid is to greatly misrepresent what the word "solid" means. The Solar System travels through the galaxy as a unit, but it absolutely isn't solid.

[Dave Lev (OP)]

It means that their motions are associated with each other, at least temporarily. To say that two objects bound by gravity is solid is to greatly misrepresent what the word "solid" means. The Solar System travels through the galaxy as a unit, but it absolutely isn't solid.

Thanks
You are absolutely correct.
It can't be solid object.
I fully accept your message that this kind of gravity bonding is temporarily:
"It means that their motions are associated with each other, at least temporarily."
Therefore, do you confirm that:
The Bar and the spiral arms are connected (or their motions are associated with each other) by mutual attraction due to gravity as one temporarily object?

[Kryptid]

The Bar and the spiral arms are connected (or their motions are associated with each other) by mutual attraction due to gravity as one temporarily object?

That does seem to be the case.

[Dave Lev (OP)]

The Bar and the spiral arms are connected (or their motions are associated with each other) by mutual attraction due to gravity as one temporarily object?

That does seem to be the case.

Thanks
Do appreciate.
Based on this case, do you also confirm that the stars there are connected (or their motions are associated with each other) by mutual attraction due to gravity between all the stars as one temporarily object?

One more question:
Please look at the following orbital velocity diagram:
https://www.astronomy.ohio-state.edu/thompson.1847/1101/RotCurve2.gif
Do you have any idea why the orbital velocity of the stars in the bar (Below 3KPC) is increasing linearity as we move further away from the Center?

[Kryptid]

I don't know if it can be said that all the stars are associated all at once. It's probably not that simple.

As for the pattern you speak of below 3 kpc, I don't know the reason for that.

[Dave Lev (OP)]

As for the pattern you speak of below 3 kpc, I don't know the reason for that.

So how our scientists claim that they know how the spiral galaxy works while they don't have a basic clue how he Bar segment works?
Don't you agree that if you explain something, you need to explain its functionality from A to Z?
As an example, if I will try to explain you how a Jumbo jet works.
However, I can only explain one segment of the fly - how the Jet can run on the run way at high velocity.
It works as follow:
We connect  the jet to a very speedy dark truck (that we can't see smell or feel) and it can pull the jet at high velocity.
Bravo for the excellent explanation!

However, don't ask me how it could continue to fly in the air as I have no clue how it works.
If you insist, I can also claim that as the dark truck lift itself on the air it also pull the jet in the air.
But please don't ask me how the dark track can lift itself in the air as it is not my job to answer this question.
Exactly in the same token, our scientists try to explain how the spiral galaxy works.
They look on the diagram and see that from 3KPC and upwards (at the spiral segment) the orbital velocity is relatively fix.
Therefore, they have invented a brilliant idea of dark matter that add the extra missing gravity force.
If you ask them how that dark matter gets over there and at that specific requested density - they will tell you that they don't know and it isn't their job to answer this kind of question.
We also understand by now that our scientists don't have a clue why the stars in the Bar accelerate linearly and dramatically to that top level of orbital velocity.
So are you sure that by explaining just one section (spiral galaxy) with something that we don't see and have no clue how it is there exactly in the specific density for each radius and each galaxy - our scientist have accomplished their mission to explain how spiral galaxies really works?

[Bored chemist]

So how our scientists claim that they know how the spiral galaxy works while they don't have a basic clue how he Bar segment works?

You seem to have equated one guy on a web site with the whole of science.

Why is that?

[Dave Lev (OP)]

So how our scientists claim that they know how the spiral galaxy works while they don't have a basic clue how he Bar segment works?

You seem to have equated one guy on a web site with the whole of science.

Why is that?

Well, it's the time for the science community to explain how the spiral galaxy really works.
Not just an explanation for just one segment that is based on some imagination that is called dark matter while we can't see, feel or smell it - but for all the other segments of the spiral arms (especially - the Bar).

If you (or anyone else) know how the Bar works, then please go ahead and share with us the knowledge.
If no one in the whole science community has a basic clue about it - why don't you give me a chance to explain how the entire spiral galaxy really works from A to Z?

[Origin]

If no one in the whole science community has a basic clue about it - why don't you give me a chance to explain how the entire spiral galaxy really works from A to Z?

Because you have demonstrated over and over that you do not know what you are talking about, so it would be a waste of time.

[Kryptid]

So how our scientists claim that they know how the spiral galaxy works while they don't have a basic clue how he Bar segment works?

You think just because I don't know the answer that literally no one knows the answer? I'm not an astrophysicist.

[Bored chemist]

Well, it's the time for the science community to explain how the spiral galaxy really works.

They did.
It's in the literature.
Go and look it up.

why don't you give me a chance to explain how the entire spiral galaxy really works from A to Z?

You have posted 4 pages worth of tosh.
Why didn't you start with the thing you just claimed you can do instead?

[Dave Lev (OP)]

You think just because I don't know the answer that literally no one knows the answer? I'm not an astrophysicist.

So who can explain the functionality of the Bar in the spiral galaxy?

They did.
It's in the literature.
Go and look it up.

I didn't find it.
Would you kindly offer the requested link to that literature with the explanation of the stars orbital velocity at that segment?