Why are we so sure that there is a need for dark matter?

[Dandav]

11 hours ago, Halc said:

So yes, there was a time when the prevailing view suggested that most stars tended to stay in the same 'arm'.

When was it and why the stars tend to stay together in the arm?

11 hours ago, Halc said:

There is no valid physics that suggests that an arbitrary subset of matter like that can exhibit gravity in isolation of other gravity.

is it?

Please look carefully at the following image:

https://www.nasa.gov/image-feature/goddard/2022/hubble-inspects-a-pair-of-space-oddities

Do you confirm the following:

1. We observe dual spiral galaxies.

2. Each galaxy has two spiral arms while each arm is located exactly at 180 degrees from the other arm.

3. Mutual gravitational attraction - It is stated: "This elongated stream of stars and interstellar dust is known as a tidal tail, and it formed by the mutual gravitational attraction of the two foreground galaxies."

Therefore, do you agree that the bridge is all about two arms that are connected/interact to each other by gravity force?

5. Please look at the other arm of each galaxy - Do you agree that it is located exactly on the other side? Therefore, can we agree that the other arm is due to tidle gravity force?

7. T-hold time = The time duration for that mutual gravitational attraction, (or how long this structure of "mutual gravitational attraction" could live in total)?

Few thousands of years, few million years or you are sure that this Mutual gravitational attraction had been formed yesterday and it will break down by tomorrow morning?

8. Do you confirm that during T-hold time the spiral arms of each galaxy can't rotate anymore?

9. Do you agree that as long as the two galaxies are connected by their mutual gravitational attraction in one arm, then the other arm can't move.

10. If the answer is yes - then why can't we claim that those two arms in each galaxy are gravitational arms?

[Halc]

I cannot give human designated subsets of matter special physics properties. The mathematics would be violated if this was done. Answers are therefore given in this light since you are attempting to give special physical properties to abstract concepts.

6 hours ago, Dandav said:

1. We observe dual spiral galaxies.

That is a matter of human designation. One person might see a single structure and others more. Most people would, in that picture, say that it is two interacting galaxies, but how the material evolves has absolutely nothing to do with this human opinion.

6 hours ago, Dandav said:

2. Each galaxy has two spiral arms while each arm is located exactly at 180 degrees from the other arm.

I count 7 arm-ish things. Two yellowish arms each for the galaxies (which you apparently don't see at all), plus more bluish material somewhat ejected to the upper left and lower right of the picture, plus the bridge between them. Only the yellow ones are the usual rotating arms. The blue concentrations of material are the tidal tails, not arms at all. You obviously label them differently, which is fine until you start giving special physical properties to your designation.

6 hours ago, Dandav said:

3. Mutual gravitational attraction - It is stated: "This elongated stream of stars and interstellar dust is known as a tidal tail, and it formed by the mutual gravitational attraction of the two foreground galaxies."

That's what the article says, yes. No disagreement until you start denying mutual gravitation with all the other galaxies as well.

6 hours ago, Dandav said:

Therefore, do you agree that the bridge is all about two arms that are connected/interact to each other by gravity force?

No You forgot to number this one as '4'. You also forgot 6 altogether.

6 hours ago, Dandav said:

5. Please look at the other arm of each galaxy - Do you agree that it is located exactly on the other side? Therefore, can we agree that the other arm is due to tidle gravity force?

I presume you're talking about the outside extensions of the bluish tidal material. They don't have an exact location since the material is spread out, so it is meaningless to say 'exactly on the other side'. All the bluish material is where it is largely due to tidal effects, as the article states. It's a classic tidal signature, just like the one the moon gives Earth.

6 hours ago, Dandav said:

7. T-hold time = The time duration for that mutual gravitational attraction, (or how long this structure of "mutual gravitational attraction" could live in total)?

Gravitation attraction never stops. There's nothing about a time limit in the equations.

6 hours ago, Dandav said:

8. Do you confirm that during T-hold time the spiral arms of each galaxy can't rotate anymore?

There is no T-hold time. The yellow actual arms continue to rotate as before. Watch the simulations which make it a lot clearer than a single still shot, but careful because most simulations use unrealistic rotation curves to simplify the programming. Simulations of realistic density waves are more compute intensive and rarely have collisions added in.

6 hours ago, Dandav said:

9. Do you agree that as long as the two galaxies are connected by their mutual gravitational attraction in one arm, then the other arm can't move.

All galaxies are effected by each other's mutual gravity. If you call that a connection, then that connection lasts forever. The blue material in the tidal clouds have little effect on the rotation of the galaxies which just keep right on spinning after a close encounter like this. The pattern would probably be more disrupted with a more direct hit, but this wasn't a very direct hit. Angular momentum is always conserved.

6 hours ago, Dandav said:

why can't we claim that those two arms in each galaxy are gravitational arms?

You can call them anything you want. The term is reasonably undefined in celestial mechanics, so sans a definition, you'd just be making a statement that's not even wrong.

[Dandav]

19 hours ago, Halc said:

.

On 12/7/2022 at 3:09 PM, Dandav said:

3. Mutual gravitational attraction - It is stated: "This elongated stream of stars and interstellar dust is known as a tidal tail, and it formed by the mutual gravitational attraction of the two foreground galaxies."

That's what the article says, yes. No disagreement until you start denying mutual gravitation with all the other galaxies as well.

On 12/7/2022 at 3:09 PM, Dandav said:

Therefore, do you agree that the bridge is all about two arms that are connected/interact to each other by gravity force?

No 

Why No?

You confirm that there is "Mutual gravitational attraction", then based on your understanding what is the meaning of that gravitational attraction and tidal tail?

What kind of force could form  "This elongated stream of stars and interstellar dust is known as a tidal tail" / Bridge?

Is it some kind of dark force due to dark matter or just a simple gravity force?

As you claim that Gravitation attraction never stops

19 hours ago, Halc said:

On 12/7/2022 at 3:09 PM, Dandav said:

7. T-hold time = The time duration for that mutual gravitational attraction, (or how long this structure of "mutual gravitational attraction" could live in total)?

Gravitation attraction never stops. There's nothing about a time limit in the equations.

Then do you agree that this bridge could last for very long time?

What about the other arm of each galaxy?

While one arm is locked in that bridge between the galaxies, do you claim that the other free arm should continue to rotate?

19 hours ago, Halc said:

Simulations of realistic density waves are more compute intensive and rarely have collisions added in.

I have asked you in the past and I will ask you again:

How the density wave + dark matter could form the unique structure of spiral galaxy?

Bulge: 0 - 1KPC

Bar: 1KPC - 3KPC

Ring - 3KPC

Spiral arms: 3KPC - 15KPC. 

Diameter of spiral arms: at 3KPC - 3000LY, at our location - 1000LY, at 15KPC - 400LY

Edited December 8, 2022 by Dandav

[Halc]

6 hours ago, Dandav said:

On 12/7/2022 at 8:09 AM, Dandav said:

Therefore, do you agree that the bridge is all about two arms that are connected/interact to each other by gravity force?

Why No?

I would not agree to a meaningless statement. "Is all about" is not a meaningful term in this context. Physical objects are not meaningfully 'about' something, be it 'all about' or just partially about. So I have no clue what you're suggesting with your statement let alone enough to agree with it.

6 hours ago, Dandav said:

based on your understanding what is the meaning of that gravitational attraction and tidal tail?

Physics does not give meaning to celestial objects. Astrology maybe does. Go ask them.

6 hours ago, Dandav said:

While one arm is locked in that bridge between the galaxies, do you claim that the other free arm should continue to rotate?

Nothing is locked. You are again trying to give rigid properties to what is essentially an effect.

6 hours ago, Dandav said:

How the density wave + dark matter could form the unique structure of spiral galaxy?

Dark matter has little to do with it. A galaxy with little to no dark matter will still show structure. A galaxy with little to no baryonic matter will not. This tells me that gravity alone is not enough, so in attempt to use your phrase, it isn't 'all about' gravity.

As for the density wave hypotheses, there is more than one model. They're not my models. Read up on them. I'm not a cosmologist, but the simulations I've seen from them look a lot more like real galaxies than do the simplified ones.

[Dandav]

On 12/9/2022 at 12:51 AM, Halc said:

Dark matter has little to do with it. A galaxy with little to no dark matter will still show structure. A galaxy with little to no baryonic matter will not. This tells me that gravity alone is not enough, so in attempt to use your phrase, it isn't 'all about' gravity.

Are you sure that "it isn't 'all about' gravity"?

Why our scientists have invented the dark matter idea?

Don't you agree that it was due to the impact of gravity on the Rotation Curve problem in the Galaxy?

 

 

Rotation following Kepler's 3rd law is shown above (blue) as planet-like or differential rotation. Notice that the orbital speeds falls off as you go to greater radii within the Galaxy. This is called a Keplerian rotation curve.

However, in order to keep the flat orbital velocity dark matter is needed.

Never the less, we can't just take dark matter and set it in the galaxy.

It is much more complicated as the dark matter density isn't constant in the galaxy.

For any galaxy at any radius there is a need for different dark matter density.

Therefore, if the spiral galaxy wish to keep its galactic orbital velocity, it needs a specific density of dark matter at any radius.

How galaxies can set so complicate calculation for the requested dark matter density?

Do they have  some sort of built in computer in order to calculate the requested dark matter formula?

Even if they can do it, don't you agree that at the end of the day dark matter is all about adding missing gravity force in the galaxy?

Therefore, why can't you agree that even the dark matter is all about gravity?

However, the dark matter can ONLY help the galaxy for the Rotation Curve problem

Unfortunately, it can't offer any solution for the complexity of spiral galaxy.

On 12/9/2022 at 12:51 AM, Halc said:

As for the density wave hypotheses, there is more than one model. They're not my models. Read up on them. 

Sorry, you don't have real theory that can deeply explain the full structure of spiral galaxy.

You don't know why the Bulge has a sphere shape while as we go further away from the we get the disc shape.

You don't know the real functionality of the bar and how it works,

You don't know why there is a ring.

You don't know why there are two main symmetrical arms that are connected to the ring exactly at the other side of the ring. If there are other arms which are connected to the ring, then they must come in a pair & be symmetrical to each other

You don't know why the spiral arms are so massive at their base (3000LY) while at the edge their diameter is only 400LY.

Not the density wave, not the MOND and not any other imagination that our scientists may invent can solve those questions.

 

On 12/9/2022 at 12:51 AM, Halc said:

I'm not a cosmologist, but the simulations I've seen from them look a lot more like real galaxies than do the simplified ones.

Based on my understanding all simulations start with a disc shape galaxy.

If this is the case, then this isn't realistic starting point.

In the following article it is stated:

https://www.smithsonianmag.com/smart-news/supercomputers-create-beautiful-simulations-spiral-galaxies-180963462/

"According to the Auriga Project website, other attempts to simulate galaxy formation have resulted in galaxies that weren’t quite right—from weird bulges to unusual spins that didn’t conform to the what astronomers observe in the skies." 

Hence, they admit that there are fatal problems with the simulations

Never the less, they have added new idea that is called magnetic fields

"The new project attempted to correct those mistakes by adding in elements other simulations did not model, especially the magnetic fields, or did not have the processing power to compute."

However, the main idea of the dark matter is that it can ONLY affects the gravity.

So how come that they have invented that magnetic fields?

I claim that this message proves that the simulation can't offer real solution.

Even so, at the best case, that spiral shape can live for just short time during the simulation.

Sonner or latter if you keep on with the simulation you loose the spiral shape.

However, we know that 70 % of the galaxies are spirals.

Therefore, they must live for billions of years.

As the simulation can show a spiral image for very short time, then this simulation is not realistic.

At the best case, the simulation can only give a brief highlight for the spiral arms shape.

Therefore, do you agree that the best simulation can't really represents the full structure of spiral galaxy (especially not the Bar, not the density of stars in spiral arms and even not the thickness of the spiral arms as we go further away in the radius)?

Therefore, why do you insist to reject the idea that the sun is interacted by gravity to the Orion arm and go with the arm wherever it goes?

If you would know that by accepting this simple idea you would understand how the entire spiral galaxies in the Universe really works with all their unique structure and without any need for dark matter would you continue to reject it?

Edited December 10, 2022 by Dandav

[Halc]

4 hours ago, Dandav said:

Notice that the orbital speeds falls off as you go to greater radii within the Galaxy. This is called a Keplerian rotation curve.

Keplerian orbits don't apply to galaxies since galaxies are not single primary masses like our own solar system. What's missing from your graph is the line showing what the curve should be given just the baryonic matter. Many similar graphs show that, but the one you've chosen does not.

4 hours ago, Dandav said:

if the spiral galaxy wish to keep its galactic orbital velocity

Galaxies don't make wishes.

4 hours ago, Dandav said:

How galaxies can set so complicate calculation for the requested dark matter density?

Galaxies don't make calculations. No requests are made of them. What's with the anthropomorphism all of a sudden?

4 hours ago, Dandav said:

Sorry, you don't have real theory that can deeply explain the full structure of spiral galaxy.

That's right. I'm no physicist. They're the ones with the real theories. The bulge/disk is pretty easy to explain. To get an explanation of the bar and such, you need to read up on the current models. I'm not doing it for you, but none of them are based only on assertions. I've not seen a viable MOND model.

4 hours ago, Dandav said:

Based on my understanding all simulations start with a disc shape galaxy.

Your understanding is very likely wrong then. A simulation of how a galaxy maintains its apparent structure would start with the structure. A simulation of galaxy formation would not start with a galaxy already formed.

4 hours ago, Dandav said:

So how come that they have invented that magnetic fields?

They were not invented. They were noticed far before galaxies were noticed.

5 hours ago, Dandav said:

However, we know that 70 % of the galaxies are spirals.

Therefore, they must live for billions of years.

Non sequitur

5 hours ago, Dandav said:

Sonner or latter if you keep on with the simulation you loose the spiral shape.

Many maintain it indefinitely

[Dandav]

17 hours ago, Halc said:

22 hours ago, Dandav said:

Sorry, you don't have real theory that can deeply explain the full structure of spiral galaxy.

That's right. I'm no physicist. They're the ones with the real theories. The bulge/disk is pretty easy to explain. To get an explanation of the bar and such, you need to read up on the current models. I'm not doing it for you, but none of them are based only on assertions. I've not seen a viable MOND model.

As you aren't physicist how do you know how spiral galaxy really works?

Let's focus on the Bar.

In the following article it is stated:

https://www.nasa.gov/mission_pages/hubble/science/bar_galaxies.html

"Bars form when stellar orbits in a spiral galaxy become unstable and deviate from a circular path. "The tiny elongations in the stars' orbits grow and they get locked into place, making a bar," explained team member Bruce Elmegreen of IBM's research Division in Yorktown Heights, N.Y. "The bar becomes even stronger as it locks more and more of these elongated orbits into place. Eventually a high fraction of the stars in the galaxy's inner region join the bar."

Therefore, our scientists clearly understand that somehow stars get locked in the Bar.

However, they don't really explain how that process works and what kind of glue is needed to lock the stars in the Bar?

Is it some sort of dark glue or magic glue?

Don't you agree that simple gravity force is needed to lock the stars to the Bar (without any need for dark matter or dark glue)

In order to make it clear:

Gravitational arm = when stars are locked together by gravity force to the arm.

Therefore, the bar is also some form of gravitational arm.

However, instead of spiral arm it is a very linear gravitational arm.

We can consider it as some sort of globular clusters of stars that are locked together by gravity force, however, instead of spherical shape it has a bar/arm shape.

Hence, why is it so difficult for those scientists to say clearly that the Bar is a linear gravitational arm where all that stars are locked to the bar by gravity force?

Edited December 11, 2022 by Dandav

[Dandav]

On 12/10/2022 at 9:15 AM, Dandav said:

Therefore, why do you insist to reject the idea that the sun is interacted by gravity to the Orion arm and go with the arm wherever it goes?

If you would know that by accepting this simple idea you would understand how the entire spiral galaxies in the Universe really works with all their unique structure and without any need for dark matter would you continue to reject it?

Why are you in a panic just from the thought that stars could be locked to the bar or to the spiral arm by simple gravity force and go with it where ever it goes? 

What might happen to the MY galaxy if our scientists would finely understand that for its proper operation, gravity is good enough and there is no need for dark matter?

Edited December 11, 2022 by Dandav

[Halc]

14 hours ago, Dandav said:

In the following [NASA] article it is stated:

"Bars form when stellar orbits in a spiral galaxy become unstable and deviate from a circular path. "The tiny elongations in the stars' orbits grow and they get locked into place, making a bar," explained team member Bruce Elmegreen of IBM's research Division in Yorktown Heights, N.Y. "The bar becomes even stronger as it locks more and more of these elongated orbits into place. Eventually a high fraction of the stars in the galaxy's inner region join the bar."

Therefore, our scientists clearly understand that somehow stars get locked in the Bar.

Nicely explained there. More than I knew. The stars in the bar may actually stay in the bar if that's right. It would explain the arms too then, similar to the wake of a turning bar in water. The bars don't move around the galaxy at all, but rather outward just like the water waves do.

That's not a statement of fact, just an observation of mine that seems to make sense to me.

14 hours ago, Dandav said:

However, they don't really explain how that process works and what kind of glue is needed to lock the stars in the Bar?

You persist in your rigid object model, which contradicts the quote you gave which says that stars move about within the bar. That much I've definitely read before in other places.

14 hours ago, Dandav said:

Don't you agree that simple gravity force is needed to lock the stars to the Bar (without any need for dark matter or dark glue)

Can't agree with that (or anything with which you ask me to agree). Dark matter is probably not needed, and dark glue is just something you made up. There's no glue at all. But more than gravity is involved, as I've said repeatedly in prior posts.

14 hours ago, Dandav said:

Gravitational arm = when stars are locked together by gravity force to the arm.

OK, at least now I have a definition of sorts for what you mean by that. No, by that definition, a gravitational arm directly contradicts observations, which you'd notice if you actually worked out the mathematical implications your assertions, all of which have been pointed out above.

[Dandav]

8 hours ago, Halc said:

23 hours ago, Dandav said:

However, they don't really explain how that process works and what kind of glue is needed to lock the stars in the Bar?

You persist in your rigid object model, which contradicts the quote you gave which says that stars move about within the bar. That much I've definitely read before in other places.

Why do you claim for rigid object?

I compare the Bar to a star cluster.

In that cluster there could be Millions of stars that are locked together by GRAVITY FORCE, while each star can move about within the cluster.

There is no need for any kind of dark matter to lock the stars in the cluster.

Therefore, do you claim that under this definition a star cluster should be consider as a rigid object?

I hope that you agree that a cluster isn't a rigid object as the bar shouldn't considered as a rigid object.

Therefore, let's agree that gravity is the ultimate force that is needed for "stars to move about within the Bar" as they can also move about within the star cluster.

However, there is a difference in the shape between the two objects.

While the cluster has a spherical shape, the bar has a bar shape.

Our mission is to understand why the Bar that technically works similarity as star cluster got its bar shape.

In order to understand that issue, lets look at the following image of the Milky way:

This image is based on real observation (and I didn't draw it by myself) - what we see is what we have!

Do you see those dots/tiny bars in the arms?

Do you agree that technically each dot could be a star cluster with millions of stars that are locked to the cluster while they all  move about within the cluster?

However, as there are quite many clusters in each arm, then each cluster is effected by gravity in both sides.

Therefore, instead of a simple spherical dot we actually got those tiny bar shape.

However, if we could take out one tiny bar from the arm and put it somewhere in the open space we would immediately get a simple star cluster.

Please remember that around the bar there is a Ring.

That ring generates some gravity force.

Therefore, why can't we consider the bar as some sort of star cluster that got its bar shape due to the impact of the Ring gravity force?

In the same token, why can't we consider the spiral arm as many star culsters that are locked together one after the other by gravity force in a long line?

Hence, the Bar and the spiral arms might look rigid but they aren't rigid as stars can move about within them.

This can also explain the motion of stars around us.

We see that each star is moving in a different direction but they wouldn't collide with each other and they would stay/locked together due to gravity force!

Don't you agree that this is exactly the expected motion of stars in a star cluster?

There are exactly 64 stars per 50 LY sphere around the Sun and 512 stars in a 100LY sphere.

As the diameter of the arm in our location is 1000LY (and based on the above density of stars), why can't we claim that this 1000LY diameter represents a star cluster with 512,000 stars while the sun with all the other nearby stars move about within that cluster?

 

 

Edited December 12, 2022 by Dandav

[Halc]

21 minutes ago, Dandav said:

There is no need for any kind of dark matter to lock the stars in the cluster.

Yes, but dark matter wasn't posited to explain why stars stay with their arms, especially since they obviously don't. Yes, stars are gravitationally bound to (they have negative mechanical energy relative to) their star cluster. Star clusters don't need glue, and my comment was about the glue comment.

25 minutes ago, Dandav said:

Our mission is to understand why the Bar that technically works similarity as star cluster got its bar shape.

It was actually explained quite nicely by the nasa quote you gave.

28 minutes ago, Dandav said:

Do you see those dots/tiny bars in the arms?

Do you agree that technically each dot could be a star cluster with millions of stars that are locked to the cluster while they all  move about within the cluster?

You mean those soap-bubbly things here and there? Those are H II regions, areas of high star formation activity. They're not clusters, nor are the oval shapes containing some of the bubbles. The picture does not identify any star clusters. Surely there's a map of them you can find.

[Dandav]

1 hour ago, Halc said:

2 hours ago, Dandav said:

Our mission is to understand why the Bar that technically works similarity as star cluster got its bar shape.

It was actually explained quite nicely by the nasa quote you gave.

No, there is no real explanation.

Let's Read it again:

"Bars form when stellar orbits in a spiral galaxy become unstable and deviate from a circular path. "The tiny elongations in the stars' orbits grow and they get locked into place, making a bar," explained team member Bruce Elmegreen of IBM's research Division in Yorktown Heights, N.Y. "The bar becomes even stronger as it locks more and more of these elongated orbits into place. Eventually a high fraction of the stars in the galaxy's inner region join the bar."

Let's look at the bulge.

There are millions or even billions of stars over there.

Most of them don't have a circular orbital path.

We can clearly see the un circular path in the S stars motion:

Therefore, when stellar orbits in a spiral galaxy become unstable and deviate from a circular path, it should set a spherical shape and not a Bar shape!

If those scientists were correct, then:

1. Why the bulge has no Bar shape?

2. Why the bar is always located between the Bulge to the Ring?

3. Why the Bar NEVER continue after the ring?

Can you please answer the above questions?

Unfortunately, those scientists totally ignore the key function of the ring.

They do not even consider that the bar is there due to the gravity force impact of the ring.

Actually, if they were correct and the ring has no impact, then technically we should see a bar structure even if there were no spiral arms and no ring.

Why do you think that the Bar has so symmetrical structure.

Don't you agree that this symmetrical structure is due to tidal force?

However, tidal with what?

Why not a tidal force with the ring?

Therefore, the ring gravity is vital for the bar structure.

Hence, stellar orbits in a spiral galaxy become unstable and deviate from a circular due to the ring gravity impact and therefore, we get the bar structure.

If you eliminate the ring and the spiral arms you won't get a symmetrical bar shape and it would be just a spherical shape.

Can you please offer even one Bar galaxy in the entier universe without ring and its spiral arms?

Edited December 12, 2022 by Dandav

[Halc]

7 hours ago, Dandav said:

Let's look at the bulge.

There are millions or even billions of stars over there.

Most of them don't have a circular orbital path.

We can clearly see the un circular path in the S stars motion:

You're not showing bulge objects in your picture. These are stars gravitationally bound to Sgr-A, and there's only perhaps a few hundred of them. There are yes, billions of stars in the bar, but those are not gravitationally bound to Sgr-A any more than are we.

How can you 'clearly' tell that those S stars don't have circular motion? A circle seen from any angle other than from a point on its axis will appear to be an ellipse, so it isn't immediately clear at all. Can you answer that?

As for the rest of the post, it is just full of wrong assertions and questions whose answer I cannot explain to you any more than I can to a squirrel.  The dynamics of stars in a galaxy is complicated and doesn't lend itself to trivial answers and polite little formulas. You don't want the real answers anyway since you deny every one of them.

We seem to have stopped making progress, so I'm probably gone after this. Go talk to JeffreysTubes8 who seems more on your level.

[Dandav]

5 hours ago, Halc said:

How can you 'clearly' tell that those S stars don't have circular motion? A circle seen from any angle other than from a point on its axis will appear to be an ellipse, so it isn't immediately clear at all. Can you answer that?

Please look at the following image:

Based on the location of Sgr-A we can clearly understand that most of those S stars has none circular motion with reference to that SMBH. Not even the closest S2 star.

5 hours ago, Halc said:

You're not showing bulge objects in your picture. These are stars gravitationally bound to Sgr-A, and there's only perhaps a few hundred of them. There are yes, billions of stars in the bar, but those are not gravitationally bound to Sgr-A any more than are we.

Yes, I fully agree.

5 hours ago, Halc said:

You don't want the real answers anyway since you deny every one of them.

That is incorrect.

I fully respect your answers. However, you ignore the key idea in my message:

13 hours ago, Dandav said:

Can you please offer even one Bar galaxy in the entire universe without ring and its spiral arms?

You Know that there is no possibility to get a Bar without the Ring and its spiral arm.

Based on the observation, the Bar is there ONLY when the ring and its spiral arms are there.

Hence, the observation proves that the bar is there due to the Ring Gravity impact!

How can we ignore the real meaning of that OBSERVATION?

[Dandav]

Let's summarize the key points about the Bar in spiral galaxy:

1. There is no bar if there is no ring and spiral arms.

2. The Bar has a symmetrical shape

So, how the Bar gets its shape?

In order to understand it, please look at the following image of the Earth due to the tidal impact of a satellite:

So, although there is just one satellite - in one side, Its tidal gravity force push the matter in the earth in both sides and set a symmetrical shape.

The Earth is quite solid object and therefore the impact on its matter due to that satellite (or even a moon) tidal force is quite minor.

However, the Bulge in the center of our galaxy isn't solid.

It is made out of millions or billions of stars that orbit somehow in that bulge.

Therefore, without any main external gravity force, there is no tidal force and the bulge would be spherical.

We see many objects that have spherical shape as globular star clusters.

In each globular cluster there are many stars that orbits around each other:

This cluster isn't affected by any main outwards gravity force and therefore, it keeps its spherical shape.

However, if we would set a massive ring of stars around this globular star cluster, then its tidal force would start to work.

As the cluster is not solid, the tidal force due to the ring would change the spherical shape of the cluster to symmetrical Bar structure.

Hence, I hope that you agree that the bar in spiral galaxy is all about two symmetrical arms that had been pushed outwards from the spherical Bulge due to the tidal force with the ring + spiral arms.

Edited December 13, 2022 by Dandav

[Dandav]

Before we try to understand how spiral galaxy works, we must understand how the Bar really works.

So, the Bar had been formed by the Ring+ spiral arms Tidal force on the Bulge.

This Tidal force pushed matter/Stars from the spherical bulge into those two symmetrical arms in order to form the Bar shape.

Hence, The Bulge had changed it spherical shape into bar shape due to that tidal force.

Now, let's try to understand the orbital rotation curve:

https://www.astronomy.ohio-state.edu/thompson.1847/1101/RotCurve2.gif..

We clearly see that up to about 3KPC the orbital velocity is increasing linearity.

Hence, if the orbital velocity at a radius of 1KPC is 80 Km/s than the orbital velocity at 2KPC is exactly 160Km/s

This proves that the stars in the bar are bonded /interacted to the bar by gravity force and increasing their orbital velocity as they are located further away in the Bar.

I would explain the orbital velocity at the spiral arms later on.

[Dandav]

On 12/5/2022 at 6:31 AM, Shustaire said:

I'm going to start here  if you calculate via Newtons gravitational laws. The baryonic mass distribution should give us a Kepler decline in rotation curves. The outer region stars would not rotate at the same rate as the internal region.

 I'm sure you have heard this before. However it has little to do with the BH at the center. If you look at the r^2 relation of [tex] f=\frac{GMm}{r^2}/[tex]you will see the force of gravity will quickly reduce to effectively zero as the radius increases. 

This is also true with the galactic bulge...

 So what matter distribution us required to keep the rotation curves in a non Kepler decline such as we see in spiral galaxies ?

The orbital velocity of any star in the galaxy is based on its local orbital motion + the revolving motion of the Bulge, Bar or spiral arm.

When we look on the motion of nearby stars, we see that each star is moving in a different direction at an average velocity of about 10 Km/s.

That local orbital motion is needed to hold/interact the star to the arm by gravity.

However, when we look from outside, we need to add to this local velocity the orbital motion of the arm

Therefore, when we look at a star that is located at the Bar, we need to add its local velocity in the bar to the revolving motion of the bar.

The local velocity is dictated by newton law and as we already know its contribution for the total velocity is quite neglected.

In order to get better understanding, let me offer the following example:

Let's assume that an observer in space is looking at our planet.

He can only see elephants while the whole planet is transparent for him.

Do you agree that even if the elephants are not moving at all, that observer would see them moving at relatively high speed due to the rotation of the planet.

In the same token when we look at a star in the Bar we actually monitor its local velocity + the bar revolving velocity.

Once we understand that key issue, we can go on and explain the other section of the galaxy.

Edited December 14, 2022 by Dandav