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# How spiral galaxy works?

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In order to answer this question, we must understand the key features of spiral galaxy.

Let's use the Milky way as an example:

What do we see?

1.  Symetrical shape:

"Milky Way Galaxy Has Mirrorlike Symmetry"

The finding suggests that the galaxy is a rare beauty with an uncommon symmetry — one half of the Milky Way is essentially the mirror image of the other half."

2. The central bulge has oval/ellipse shape. Its major radius is 3KPC while its minor radius is only 1KPC. We clearly see that it is one single object. However, we can divided it to two sections: Bulge and Bar.

Bulge – up to 1KPC. In the bulge the stars orbit at all directions.

Bar – From 1KPC to 3KPC. The velocity of the stars in this section is increasing literally as we move further away from the center. At the edge of the bar the velocity of the stars is maximal (about 220 Km/s).

3. Ring – At 3KPC we clearly see the two ring arms that are called 3KPC arm.

4. Spiral arm –  Two main spiral arms are ejected exactly from the edge of the Bar.

It is stated: "The finding suggests that Scutum-Centaurus wraps all the way around the Milky Way, making it a symmetric counterpart to the galaxy’s other major star-forming arm, Perseus. The two arms appear to extend from opposite ends of the galaxy’s central, bar-shaped cluster of stars, each winding around the galaxy"

My question is as follow:

How the oval shape of the central bulge/bar and the symmetrical shape of the galaxy are created?

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9 hours ago, Dandav said:

In order to answer this question, we must understand the key features of spiral galaxy.

Let's use the Milky way as an example:

What do we see?

1.  Symetrical shape:

"Milky Way Galaxy Has Mirrorlike Symmetry"

The finding suggests that the galaxy is a rare beauty with an uncommon symmetry — one half of the Milky Way is essentially the mirror image of the other half."

2. The central bulge has oval/ellipse shape. Its major radius is 3KPC while its minor radius is only 1KPC. We clearly see that it is one single object. However, we can divided it to two sections: Bulge and Bar.

Bulge – up to 1KPC. In the bulge the stars orbit at all directions.

Bar – From 1KPC to 3KPC. The velocity of the stars in this section is increasing literally as we move further away from the center. At the edge of the bar the velocity of the stars is maximal (about 220 Km/s).

3. Ring – At 3KPC we clearly see the two ring arms that are called 3KPC arm.

4. Spiral arm –  Two main spiral arms are ejected exactly from the edge of the Bar.

It is stated: "The finding suggests that Scutum-Centaurus wraps all the way around the Milky Way, making it a symmetric counterpart to the galaxy’s other major star-forming arm, Perseus. The two arms appear to extend from opposite ends of the galaxy’s central, bar-shaped cluster of stars, each winding around the galaxy"

My question is as follow:

How the oval shape of the central bulge/bar and the symmetrical shape of the galaxy are created?

You are forgetting a major part of spiral galaxies which is the super massive black hole in the middle which binds the entire galaxy together.

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2 minutes ago, Vmedvil said:

You are forgetting a major part of spiral galaxies which is the super massive black hole in the middle which binds the entire galaxy together.

Can you give us a citation for that? From what I understand it's the dark matter that drives the galaxy's shape and rotation rates. You might be right but you need to provide some context for your assertion.

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5 minutes ago, Moontanman said:

Can you give us a citation for that? From what I understand it's the dark matter that drives the galaxy's shape and rotation rates. You might be right but you need to provide some context for your assertion.

Link = https://www.cosmotography.com/images/supermassive_blackholes_drive_galaxy_evolution_2.html , Here is a brief article about how supermassive black holes drive galactic evolution.

Here is another one, Link = Black Holes Shed Light on Galaxy Formation | HubbleSite

Edited by Vmedvil
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7 minutes ago, Vmedvil said:

Without dark matter galaxies would fly apart, evidently both play an important part of galaxy shape and rotation.

Quote

Galaxies in our universe seem to be achieving an impossible feat. They are rotating with such speed that the gravity generated by their observable matter could not possibly hold them together; they should have torn themselves apart long ago. The same is true of galaxies in clusters, which leads scientists to believe that something we cannot see is at work. They think something we have yet to detect directly is giving these galaxies extra mass, generating the extra gravity they need to stay intact. This strange and unknown matter was called “dark matter” since it is not visible.

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5 minutes ago, Moontanman said:

Without dark matter galaxies would fly apart, evidently both play an important part of galaxy shape and rotation.

Well, some think that dark matter may be hawking radiation from black holes, link = Dark radiation and superheavy dark matter from black hole domination | Journal of High Energy Physics (springer.com) and [2107.00013] Primordial Black Hole Evaporation and Dark Matter Production: I. Solely Hawking radiation (arxiv.org)

Thus, it could be where the black hole creates the dark matter halo.

Edited by Vmedvil
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19 minutes ago, Vmedvil said:

Well, some think that dark matter may be hawking radiation from black holes, link = Dark radiation and superheavy dark matter from black hole domination | Journal of High Energy Physics (springer.com) and [2107.00013] Primordial Black Hole Evaporation and Dark Matter Production: I. Solely Hawking radiation (arxiv.org)

Thus, it could be where the black hole creates the dark matter halo.

Interesting, always good to learn something new, I'll have to keep an eye out for more info along these lines.

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8 minutes ago, Vmedvil said:

Not as tough as the physics forums tho, they just ban everything that moves is what I believe.

But then again that's why I like this science forums it is much more relaxed you can actually talk about speculative and inventive ideas without being banned.

Only if you can support your ideas with math, citation, or evidence 😇

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1 hour ago, Vmedvil said:

Thus, it could be where the black hole creates the dark matter halo.

1 hour ago, Moontanman said:

From what I understand it's the dark matter that drives the galaxy's shape and rotation rates.

Would you kindly explain how the SMBH and/or the dark matter could explain the oval shape of the central bulge and the symmetrical shape of the galaxy?

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7 minutes ago, Dandav said:

Would you kindly explain how the SMBH and/or the dark matter could explain the oval shape of the central bulge and the symmetrical shape of the galaxy?

Gravity and rotation, everything in the universe rotates, everything in the universe is affected by gravity, normal matter is influenced by friction as well, the three forces fight each other this results in disc shaped objects and groups of objects. Think of the solar system, all the planets are on a plane called the ecliptic, the sun is the central bulge the planets are like the arms of the galaxy.

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4 hours ago, Moontanman said:

Gravity and rotation, everything in the universe rotates, everything in the universe is affected by gravity, normal matter is influenced by friction as well, the three forces fight each other this results in disc shaped objects and groups of objects.

Can you please specify how Gravity and rotation could set the unique oval structure of the central bulge and the symmetrical shape of the galaxy?

Do you mean - Tidal gravity force???

4 hours ago, Moontanman said:

Think of the solar system, all the planets are on a plane called the ecliptic, the sun is the central bulge the planets are like the arms of the galaxy.

In the solar system, each planet can orbit at elliptical orbital shape, but each one has its own orbital motion and there is no symmetrical motion between the planets

Please also be aware that the further the planet is located from the sun, the slower it orbits.

In the galaxy' central bulge, all the stars are moving together and set this unique oval shape while as they are located further away from the center, their velocity is increasing.

That by itself is a sever contradiction to gravity law.

How could it be that an object in the bar / oval shape, would orbit faster as it is farther away from the center?

With regards to the dark matter:

It is stated that the dark matter helps to keep the constant orbital velocity of the stars at any radius in the spiral arms.

However, at 3KPC we see the ring. In the internal side of that ring - there is the oval shape of the Bar/ ventral bulge, while in the outer side - the symmetrical spiral arms are located.

Please remember - at the bar, the orbital velocity is increasing linearly as we move outwards. At the edge of the bar, we see the ring and the velocity there is maximal (about 220Km/s). however, once the star is located at the spiral arm, its orbital velocity is kept at that 220Km/s at any radius.

So how the dark matter can support those three segments (Bar + RING + Symetrical Spiral) with the unique features of each one of them, while all of them meets at 3KPC?

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3 hours ago, Dandav said:

Can you please specify how Gravity and rotation could set the unique oval structure of the central bulge and the symmetrical shape of the galaxy?

Do you mean - Tidal gravity force???

In the solar system, each planet can orbit at elliptical orbital shape, but each one has its own orbital motion and there is no symmetrical motion between the planets

Please also be aware that the further the planet is located from the sun, the slower it orbits.

In the galaxy' central bulge, all the stars are moving together and set this unique oval shape while as they are located further away from the center, their velocity is increasing.

That by itself is a sever contradiction to gravity law.

How could it be that an object in the bar / oval shape, would orbit faster as it is farther away from the center?

With regards to the dark matter:

It is stated that the dark matter helps to keep the constant orbital velocity of the stars at any radius in the spiral arms.

However, at 3KPC we see the ring. In the internal side of that ring - there is the oval shape of the Bar/ ventral bulge, while in the outer side - the symmetrical spiral arms are located.

Please remember - at the bar, the orbital velocity is increasing linearly as we move outwards. At the edge of the bar, we see the ring and the velocity there is maximal (about 220Km/s). however, once the star is located at the spiral arm, its orbital velocity is kept at that 220Km/s at any radius.

So how the dark matter can support those three segments (Bar + RING + Symetrical Spiral) with the unique features of each one of them, while all of them meets at 3KPC?

The factors i mentioned cause spirals in everything from hurricanes to galaxies, I would suggest you do some research. Here is a good place to start.

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5 hours ago, Moontanman said:

The factors i mentioned cause spirals in everything from hurricanes to galaxies, I would suggest you do some research. Here is a good place to start.

Thanks

"In a spiral galaxy, everything orbits at the same speed, meaning stars and gas near the center of the galaxy complete an orbit in less time than objects farther out. This effect is referred to as differential rotation. So, in the time it takes an inner star to complete one revolution around its galaxy, an outer star might have only finished half a revolution."

If differential rotation were the only process involved in generating spirals, we would expect to see many tightly wrapped spiral arms, like a wound coil. But most spiral galaxies have only two to four main arms.

So far, the science community couldn't find a single solution for that enigma.

Therefore, it is stated:

"Spiral arms in galaxies can form by a combination of processes."

"the arms are the result of a persistent pattern of stars rather than particular stars causing the structures. That pattern is caused by a density (pressure) wave that spirals from the edge of the disk to the center and back out again, creating the visible spiral arms of the galaxy. Essentially, as stars and gas move through the pattern, they bunch up in the wave crests, like a stellar traffic jam, and then eventually break past the crest and continue on their orbit."

Unfortunately, that density wave with its traffic jam concept is some sort of statistical activity that can't really explain the full complexity of the spiral galaxy

It can't explain why the Milky way has two symmetrical spiral arms, how the central bulge got its oval shape, why there is a ring at 3KPC, why just below the 3KPC  (at the bar) the orbital velocity of the star is increasing as it moves outwards and many more questions.

could it be that the science community just failed to understand how spiral galaxy really works?

8 hours ago, OceanBreeze said:

That begs the question: While there is an abundance of indirect evidence for dark matter; can we absolutely rule out the possibility that a better model may be produced in future that does not include dark matter?

Yes, there is a better model / idea and it is called - tidal gravity force.

As there is no direct evidence for dark matter, why the science community refuse to open their mind to this real idea?

Edited by Dandav
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50 minutes ago, Dandav said:

Thanks

"In a spiral galaxy, everything orbits at the same speed, meaning stars and gas near the center of the galaxy complete an orbit in less time than objects farther out. This effect is referred to as differential rotation. So, in the time it takes an inner star to complete one revolution around its galaxy, an outer star might have only finished half a revolution."

If differential rotation were the only process involved in generating spirals, we would expect to see many tightly wrapped spiral arms, like a wound coil. But most spiral galaxies have only two to four main arms.

So far, the science community couldn't find a single solution for that enigma.

Therefore, it is stated:

"Spiral arms in galaxies can form by a combination of processes."

"the arms are the result of a persistent pattern of stars rather than particular stars causing the structures. That pattern is caused by a density (pressure) wave that spirals from the edge of the disk to the center and back out again, creating the visible spiral arms of the galaxy. Essentially, as stars and gas move through the pattern, they bunch up in the wave crests, like a stellar traffic jam, and then eventually break past the crest and continue on their orbit."

Unfortunately, that density wave with its traffic jam concept is some sort of statistical activity that can't really explain the full complexity of the spiral galaxy

It can't explain why the Milky way has two symmetrical spiral arms, how the central bulge got its oval shape, why there is a ring at 3KPC, why just below the 3KPC  (at the bar) the orbital velocity of the star is increasing as it moves outwards and many more questions.

could it be that the science community just failed to understand how spiral galaxy really works?

Yes, there is a better model / idea and it is called - tidal gravity force.

As there is no direct evidence for dark matter, why the science community refuse to open their mind to this real idea?

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11 hours ago, Dandav said:

Thanks

"In a spiral galaxy, everything orbits at the same speed, meaning stars and gas near the center of the galaxy complete an orbit in less time than objects farther out. This effect is referred to as differential rotation. So, in the time it takes an inner star to complete one revolution around its galaxy, an outer star might have only finished half a revolution."

If differential rotation were the only process involved in generating spirals, we would expect to see many tightly wrapped spiral arms, like a wound coil. But most spiral galaxies have only two to four main arms.

So far, the science community couldn't find a single solution for that enigma.

Therefore, it is stated:

"Spiral arms in galaxies can form by a combination of processes."

"the arms are the result of a persistent pattern of stars rather than particular stars causing the structures. That pattern is caused by a density (pressure) wave that spirals from the edge of the disk to the center and back out again, creating the visible spiral arms of the galaxy. Essentially, as stars and gas move through the pattern, they bunch up in the wave crests, like a stellar traffic jam, and then eventually break past the crest and continue on their orbit."

Unfortunately, that density wave with its traffic jam concept is some sort of statistical activity that can't really explain the full complexity of the spiral galaxy

It can't explain why the Milky way has two symmetrical spiral arms, how the central bulge got its oval shape, why there is a ring at 3KPC, why just below the 3KPC  (at the bar) the orbital velocity of the star is increasing as it moves outwards and many more questions.

could it be that the science community just failed to understand how spiral galaxy really works?

Yes, there is a better model / idea and it is called - tidal gravity force.

As there is no direct evidence for dark matter, why the science community refuse to open their mind to this real idea?

Edited by Vmedvil
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On 1/14/2024 at 11:31 PM, Moontanman said:

Dear Moontanman

I have asked a simple question:

"On 1/13/2024 at 9:21 PM, Dandav said: How the oval shape of the central bulge/bar and the symmetrical shape of the galaxy are created?"

On 1/14/2024 at 11:31 PM, Moontanman said:

I really appreciate your efforts to answer my question, but it is about the spiral arms modeling and not about the central bulge/bar oval and the symmetrical shape.

Therefore, do you agree that so far there is no answer for this question?

On 1/14/2024 at 11:31 PM, Moontanman said:

If you have a better model please provide a link to it,

As there is no answer for this question, then can we agree that currently there is no modeling for that oval central bulge/Bar & the symmetrical shape of the galaxy?

So, it's not about better modeling, it's about no modeling / idea for my question.

On 1/14/2024 at 1:53 PM, Dandav said:

So how the dark matter can support those three segments (Bar + RING + Symetrical Spiral) with the unique features of each one of them, while all of them meets at 3KPC?

Do we have an answer for that?

If no, then this by itself proves that there is a severe problem with the dark matter modeling.

On 1/14/2024 at 11:31 PM, Moontanman said:

if you have a better model then this thread becomes more than a bit dishonest,

Why can't I verify if there is any current modeling that can answer my question before discussing about my personal ideas.

On 1/14/2024 at 11:31 PM, Moontanman said:

if you have a model that answers your question then why not provide it

On 1/14/2024 at 11:31 PM, Moontanman said:

If you have a better answer then give it

My idea is as follow:

Let's assume that we could take out the spiral arms and the ring from the milky way galaxy.

In this case, we would have only the central bulge.

Without any sort of external gravity impact, it is expected that the central bulge would have a ball shape like other globular star clusters.

So, we can start our discussion with massive globular cluster in a ball shape with billions of stars.

Now, let's assume that we can set smaller star cluster in an orbital motion around that massive globular cluster.

What would be the impact?

Don't you agree that due to tidal impact, the central massive globular cluster would get an oval shape.

So, do you confirm that the milky way central bulge could get its oval shape due to tidal force impact with the two main spiral arms in both sides?

This also can explain why there are only two main spiral arms in both sides of the galaxy, and why the central oval shape and the whole galaxy is symmetrical.

Edited by Dandav
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On 1/15/2024 at 3:37 AM, Dandav said:

Thanks

"In a spiral galaxy, everything orbits at the same speed, meaning stars and gas near the center of the galaxy complete an orbit in less time than objects farther out. This effect is referred to as differential rotation. So, in the time it takes an inner star to complete one revolution around its galaxy, an outer star might have only finished half a revolution."

If differential rotation were the only process involved in generating spirals, we would expect to see many tightly wrapped spiral arms, like a wound coil. But most spiral galaxies have only two to four main arms.

So far, the science community couldn't find a single solution for that enigma.

Therefore, it is stated:

"Spiral arms in galaxies can form by a combination of processes."

"the arms are the result of a persistent pattern of stars rather than particular stars causing the structures. That pattern is caused by a density (pressure) wave that spirals from the edge of the disk to the center and back out again, creating the visible spiral arms of the galaxy. Essentially, as stars and gas move through the pattern, they bunch up in the wave crests, like a stellar traffic jam, and then eventually break past the crest and continue on their orbit."

Unfortunately, that density wave with its traffic jam concept is some sort of statistical activity that can't really explain the full complexity of the spiral galaxy

It can't explain why the Milky way has two symmetrical spiral arms, how the central bulge got its oval shape, why there is a ring at 3KPC, why just below the 3KPC  (at the bar) the orbital velocity of the star is increasing as it moves outwards and many more questions.

could it be that the science community just failed to understand how spiral galaxy really works?

Yes, there is a better model / idea and it is called - tidal gravity force.

Tidal forces acting to cause the spirals is not a new idea. I found the below information on Scientific American, but a log in was required so I cannot post a link:

According to Jerry Sellwood, who studies stellar group dynamics at Rutgers University, “precisely what pulls on what to make the arms develop, the how part of your question, is much harder. There are several competing theories, all of which undoubtedly contain elements of truth, but none has gained wide acceptance.”

"In the case of Messier 51, most experts agree that tides raised by the small companion galaxy are probably responsible for some of its exceptionally regular pattern, but too many galaxies display spiral arms for them all to be caused by interactions. Bars at the centers of galaxies are another idea that may drive spirals, but Messier 33 provides a clear counter-example to indicate that bars are not a universal mechanism either. I personally hope that the explanation will eventually be found in a recurrent dynamic instability (a flag flaps in a breeze because of a recurrent instability), but this idea still needs a lot more work.”

Quote

As there is no direct evidence for dark matter, why the science community refuse to open their mind to this real idea?

I think that scientists for the most part, do have open minds and are receptive to new theories. By searching for dark matter they will either find it and confirm it exists, or they will be forced to move on to another idea. Keep in mind that the term "dark matter" can just be used as a general name for whatever they eventually discover.

Moderator note: I have deleted several off-topic posts from this thread. I think this is an interesting topic and I would like to keep the discussion on topic, if possible. Thank you for your cooperation!

Edited by OceanBreeze