Why Spiral Galaxies?

[WillieB]

This post is made as the result of the fact that I simply enjoy the process of thinking. There is also a second motive. I am determined to continue posting until the process of fully developing the concepts put forward at (also see the thread "Keep it Simple). The Incremental Universe is completed. I am the first to admit that the substance of this post has absolutely no basis in proven scientific fact but it seems logical to me.

 

Contrary to the above I firmly believe that my previous posts on the thread “Keep it Simple” do carry a modicum of scientific validity simply because their positions mesh so closely with so many previously proven but unexplained physical phenomena. In any case what follows was derived through parallel reasoning to that which led to that previous posting. And, again, thinking is a lot of fun.

 

This thread attempts to elicit a conversation as to a possible explanation for the existence of such a preponderance of spiral galaxies (seventy-seven percent) as opposed to elliptical or irregular galaxies. Fortunately or unfortunately, depending upon your point of view, you must absorb the principles enunciated in the original paper before you can fully or satisfactorily respond on this subject.

 

Duplicated below are two short discussion items excerpted from that paper:

 

7. Supernovas and Black Holes (from part D)

 

The Novas or supernovas that periodically exhibit themselves occur when the density of the star increases to reach the point that a major portion of the star’s increment’s orbits are compressed and collapsed, freeing the pb’s to fly off to wreak their havoc on the surrounding field. The remaining increments could assume intimate relationships to form neutrons and the conglomerate would become a neutron star. Eventually all of the increments could cease any mutual relationships forming matter as we know it which would result in a mass of increments crowding together to form a barrier that is virtually impenetrable by the free increments, hence, a black hole.

 

 

10. The Power of the Magnetic Field (from part D)

 

What could possibly explain those great linear eruptions that extend through the universe for thousands of light years? Something somehow generated a tremendously powerful magnetic field causing all the increments within its grasp to be perfectly polarized. And then something set off a condition that collapsed the orbits of these gazillion increments. The paired bundles on the exteriors of their orbits flew off in all directions. But those that were on the interior portion of their orbits were all traveling on opposed but parallel vectors and they were directed precisely in opposite directions to form a tremendously long and energetic expression of released energy .

 

The conjecture that I would like to put forward here would envision that a massive supernova has, in the distant past, occurred at what is now the core of each and every spiral galaxy. This supernova consumed the majority of the mass involved in that proto-galaxy. I can’t specify the type of body in which this mass was contained but my speculation is that it was a massive star similar to, but much larger than our sun. The material of which it was composed was most likely in the form of plasma and its rotation created a powerful magnetic field which perfectly polarized all of the increments forming this material. When the eruption came the paired bundles (the pb’s) that were on the interior of their orbits were traveling at a velocity of 2c x (Square root of 2) on a vector parallel to the orientation of its increment. They became free to form two streams of pb’s shooting off in opposite directions. The increments which were on the exterior portion of their orbits were traveling on varying vectors at velocities ranging from zero (or a negative velocity) to a velocity approaching c x (square root of 2). They spread out in all directions to form what is now the core of the galaxy.

 

The interior pb’s shooting out in opposite direction also possessed a radial velocity due to the rotation of the parent star. They eventually formed a gracious spiral around the point of the supernova and became the building blocks for the orbiting matter composing the galaxy itself. Some of the galaxies obviously experienced two or more such supernovas.

 

What about you? Do you have an equally logical explanation?

[Boerseun]

A bit of a long post, but interesting, nonetheless.

 

The structure of a spiral galaxy is due to an enormous collection of mass at its center. The rest of the galaxy then rotates around that mass, and following Kepler, those stars closer to the center will orbit the center faster than those further away. Same with the Earth orbiting the Sun once a year, but Neptune taking 84 years. Hence the creation of a spiral.

 

It could be that the non-spiral cluster galaxies are much younger, with a much more even distribution of mass. The constituent stars will then make up binary pairs, which in turn orbit other binaries, making up bigger and bigger (and more complex) relationships, with the whole galaxy ending up rather spherically.

 

But a classical spiral galaxy is merely due to the uneven distribution of mass, and the rest of the constituent matter orbiting that central mass.

[Eclogite]

The conjecture that I would like to put forward here would envision that a massive supernova ...........They (the pbs) eventually formed a gracious spiral around the point of the supernova and became the building blocks for the orbiting matter composing the galaxy itself. Some of the galaxies obviously experienced two or more such supernovas.

What mechanism retains the spiral form for billions of years, given the winding problem?

[Buffy]

What mechanism retains the spiral form for billions of years, given the winding problem?

Because the arms themselves are kind of optical illusions: they are density waves made up of the varying orbits of the stars within the galaxies. Great wiki page on Spiral Galaxies describes how it works (I had the pleasure of taking Astro 101 from the Frank Shu mentioned as the author of this theory at Berkeley, he was one of my favorite profs...).

 

Densely waving, :shocked:

Buffy

[CraigD]

Do you have an equally logical explanation [for the predominance of spiral galaxies in the universe]?

Though I can’t claim authorship of the explanation, from reading recent astronomy literature, I believe the growing consensus among astronomers is that all galaxies form as amorphous disks, then provided a sufficient infall of gas from the surrounding space exists, form first (at about 2 billion years) “bars and spiral waves”, then (at about 5BY) a bar, then (at about 8BY) a barred spiral, which slowly becomes nearly a pure spiral (At about 11BY). If sufficient gas continues to infall, a galaxy will continue to form and lose bars, although as the universe is thought to be only about 13-14BY old, this cycle has happened only a few times in the oldest galaxies. (source: “Ripples in a Galactic Pond”, Françoise Combes, 10/2005 Scientific American – subscription required for full article – a pitty, as it has very nice illustrations :shocked:) Most galaxies are actually barred, not nearly pure spirals. Our own Milky Way, once thought to be a pure spiral, is now believed to have a distinct (about 30% diameter) bar.

What mechanism retains the spiral form for billions of years, given the winding problem?

Again not speaking from personal expertise, the continued infall of intergalactic gas appears to result in process of periodic continuing reformation of spiral galaxies.

 

Interestingly, a growing source of data forming the current consensus about the shape of galaxies is coming from increasingly detailed computer simulations, where decades ago, computer simulations played a small role compared to deep space telescopic studies. As available computer power is likely to continue to grow faster than advances in telescopy, I expect this trend will continue for some time.

 

The conjecture that I would like to put forward here would envision that a massive supernova has, in the distant past, occurred at what is now the core of each and every spiral galaxy. This supernova consumed the majority of the mass involved in that proto-galaxy. I can’t specify the type of body in which this mass was contained but my speculation is that it was a massive star similar to, but much larger than our sun. The material of which it was composed was most likely in the form of plasma and its rotation created a powerful magnetic field …

I don’t think this conjecture is supported by theory or evidence. Even the larges single supernova’s are, in terms of galactic dynamics, insignificant. Though explaining theory is not yet well developed, observation and best theory indicate that there are no stars larger than 150 solar masses (source wikipedia article “Star”, section “Mass”). Theory and observation strongly that supernovas often occur in “chain reactions”, but still, don’t significantly effect the shape of galaxies due to their explosive energy (though the gas and dust they scatter likely contributes).

… This supernova consumed the majority of the mass involved in that proto-galaxy…

That supernovas consume much mass is, I’m fairly sure, a misconception. The energy output of the largest supernovas is about 10^46 J, equivalent to “only” about 5% of the mass of our own sun (source: wikipedia article “Supernova”). Supernovas don’t so much consume mass, as redistribute it.

 

This is not to rule out the role of strong magnetic fields generated by massive objects in galactic cores. The supermassive black holes believed to exists in the cores of all but the youngest galaxies are known to be capable of prolonged energetic events dwarfing those of supernovas, and are believed to involve powerful magnetic fields. Even these huge objects, though, appear to play a smaller role than the infall of gas. It’s important to note that, according to current theory and observation, the mass of gas between galaxies (within just a galactic cluster – not including gas between clusters) exceeds in all of the stars and other bodies within the galaxies.

[WillieB]

Craig D

 

Thanks very much for your informativoe and well phrased reply. However I still am facing some questions in my mind.

 

First, it is true that our knowlege of supernova and of galaxy formation is limited to those volumes of space which is observable from our vantagepoint. I have progressed to the point that I have very serious doubts as to the validity of the Big Bang Hypothesis. I now have arrived at a point that I am leaning toward something approaching the Steady State Hypothosis in which matter is being created as the universe expands. This leads to a possibility that the universe is much older that 13.7 B years and who knows what the characteristics of star formation and supernovae existed during this long ago universe. Perhaps a star composed of pure hydrogen and nothing but hydrogen exhibited much different characteristics than stars formed in later generations containing their share of helium, lithium and heavier elements. This may have permitted much larger and more energetic supernovae.

 

Of course that is all conjecture, but conjecturing is what I love to do and it can do no harm and may lead to some interesting conclusions.

 

If the proto galaxies are formed simply by aggregating gas from the surrounding space what imparts the angular momentum that results in the fat disc space that most galaxies assume? Why don't they retain a confused and garbled shape of a sphere similar to our elliptical galaxies? Why the existence of the barred galaxies that eventually devolve into spirals? It would seem that the supernova is the perfect answer to those questions?

[CraigD]

… conjecturing is what I love to do and it can do no harm and may lead to some interesting conclusions.

Conjecturing is what hypography is all about. If we didn’t like it, our scientific interest could be satisfied with a steady diet of textbooks, which, while it might impart an impressive amount of knowledge, would be pretty dull :)

If the proto galaxies are formed simply by aggregating gas from the surrounding space what imparts the angular momentum that results in the fat disc space that most galaxies assume? Why don't they retain a confused and garbled shape of a sphere similar to our elliptical galaxies?

This question has a satisfying conventional answer, accessible either through simple computer simulations or simpler exercises of imagination.

 

We know from their spectrum (which is concentrated in the x-ray band) that the infalling gas in a proto-galaxy though very tenuous (a few thousand H atoms per m^3, super-hard vacuum by ordinary standards), it is also very hot (10^5 to 10^7° K). The velocity and momentum of the particles of the gas, though fairly random in direction, is very great, so that even a small random deviation from complete homogeneity results in large angular momentums of the coalescing galaxies. So, although a galaxy with little or no angular momentum is possible, it is statistically very unlikely, explaining why such galaxies are not observed.

 

The question can be turned around to ask “Since statistics dictate that galaxies have a flattened disk shape, why are hundreds of nearly spherical collections of stars, such as globular clusters, observed in the halos of the Milky Way and nearby galaxies?”

 

Here again, interstellar gas would appear to be key to the explanation, along with the difference in size between even the largest of these spherical bodies and even the smallest galaxies. The explanation is left as an exercise for the reader.

Why the existence of the barred galaxies that eventually devolve into spirals? It would seem that the supernova is the perfect answer to those questions?

I believe Boerseun gives a simple and correct explanation in post #2 – the rearrangement of stars from a elliptical bar formation into a spiral is an inevitable consequence of orbital mechanics.

 

Supernovae, while apparently critical for the synthesis of heavy elements in later generation stars and planetary systems, are just not, IMHO, energetic enough to have a significant effect on the shapes of galaxies. The periodical ripples that appear disturb the intergalactic gas of a galaxy clusters contain more kinetic energy than are produced by billions of supernovae, while the supermassive black holes in galactic cores may emit comparable amounts energy in the form of gas jets. Even the periodic chain reactions of supernovae that appear to occur from time to time in galaxies are dwarfed by these phenomena.

[Buffy]

Why the existence of the barred galaxies that eventually devolve into spirals? It would seem that the supernova is the perfect answer to those questions?

I believe Boerseun gives a simple and correct explanation in post #2 – the rearrangement of stars from a elliptical bar formation into a spiral is an inevitable consequence of orbital mechanics.

Um, not quite. As I mentioned in Post #4, while the underlying mechanism is orbits of stars obeying Kepler's laws, the visible spiral structures are *wave effects* due to stars passing through places where their density is higher resulting in "bright" spots. But the important thing to realize is that it is *not* stars "flying in formation"--otherwise you'd have the winding effect that Eclogite mentions in Post #3.

 

What causes the spirals to form is that the distances from the center cause these elliptical stellar orbits to rotate (yes, that's the *orbit* rotating, not the star), relative to one another, and these orbits become closer or further apart resulting in the appearance of the arms. You can see this in the diagram in the wiki link in post #4.

Source: Wikipedia/Spiral Galaxies

 

Early in the formation of galaxies, these ellipses are often more aligned, resulting in bars that get dragged into spirals:

Bars are thought to be a temporary phenomenon in the life of spiral galaxies, the bar structure decaying over time, transforming the galaxy from a barred spiral to a "regular" spiral pattern.

This is due to that "orbits rotating" effect.

 

Apperances are not always what they appear to be,

Buffy

[CraigD]

Why the existence of the barred galaxies that eventually devolve into spirals? It would seem that the supernova is the perfect answer to those questions?

I believe Boerseun gives a simple and correct explanation in post #2 – the rearrangement of stars from a elliptical bar formation into a spiral is an inevitable consequence of orbital mechanics.

Um, not quite. As I mentioned in Post #4, while the underlying mechanism is orbits of stars obeying Kepler's laws, the visible spiral structures are *wave effects* due to stars passing through places where their density is higher resulting in "bright" spots. But the important thing to realize is that it is *not* stars "flying in formation"--otherwise you'd have the winding effect that Eclogite mentions in Post #3.

I think Boeresun and I were simply wrong, and Buffy and wikipedia right, about how galaxies eventually acquire their spiral arms. In our defense, I can only offer that this galactic motion stuff is darned complicated! :)

 

Had I more carefully read (and remembered) the “Ripples in a Galactic Pond” article I cited in post #5, I’d not have erred, as this article has a nicely illustrated explanation similar to the wikipedia article’s. Where it’s author (Françoise Combes) exceeds and slightly contradicts wikipedia is in proposing that central bar structures recur, and will continue to recur, as a result of infalling gas, in addition to chance alignment of “density waves” or interactions with nearby galaxies.

 

A simple comparison of the orbital period of the sun around the galactic center vs. the observed movement of the spiral arms also uncovers the misconception.

 

The whole, complicated subject is a delight of strange, wonderful, and difficult to master concepts! I particularly enjoyed Tucker, Tanabaum and Fabian’s calculation (in RIAGP) of the “speed of sound in vacuum” of intergalactic space of the Perseus cluster of 1170 km/s, and of the frequency of a particular observed “ripple” as “B-flat, at 57 octaves below middle C”, or about 1 cycle per 10 million years!

[Jay-qu]

I think Boeresun and I were simply wrong, and Buffy and wikipedia right, about how galaxies eventually acquire their spiral arms. In our defense, I can only offer that this galactic motion stuff is darned complicated! :(

 

Well there is still a lot to learn about galactic development, its not the kind of thing one can sit back and watch

 

Spirals dont "wind up", otherwise you run into a winding problem - otherwise old spirals would be observed with much more tightly wound arms.

 

The way we learned it at uni was: Im not sure what sets up the initial spiral arms, but it has to do with a slower rate of star formation. Once the arms have been set pattern is perpetuated by the formation of new stars that is caused by the compression of interstellar gases by the supernovae of the preceding stars.

[Eclogite]

Because the arms themselves are kind of optical illusions: they are density waves made up of the varying orbits of the stars within the galaxies.

Exactly so, but Willie B's hypothesis seems only to explain the initial generation of spiral arms. It does not appear to provide a sustaining mechanism.

If he wishes to use the conventional explanation (which can quite happily generate and sustain the spiral structure) one is left wondering why he needs to introduce his separate hypothesis.

[WillieB]

I wish to extend my thanks to Boerseun, Eclogite, Buffy, JayQu and especially to Craig D for participating in this most interesting discussion. I have done all of the reading that was recommended and I can easily visualize how the huge “cloud” of gas condenses or accretes into the classic spiral configuration. What I cannot visualize or completely buy into is the obviously accepted conclusion that a bar formation will intercede between the accretion stage and the spiral stage without some type of impetus other than that provided by gravity and momentum. I quote below from Francois Combes article in Scientific American.

 

“……in most the spiral begins in a bar—a long, luminous rectangle of stars.”

 

I most certainly cannot buy the “rectangular” portion of that conclusion. As far as the “bar,” perhaps if we conclude that, during the accretion stage, a huge conglomeration of gas, and perhaps even a black hole existed in the core which generated a magnificent magnetic field, then I may be able to accept that a bar formation would precede the decay into a spiral. I think our discussion has reached a logical end, but if you have anything further have at it. I would love it!

 

WillieB

[freeztar]

Well this was a good thread to read. I must admit that I'm a bit confused about the induction of interstellar gases influencing the galaxy's shape. :)

 

After reading Buffy's original post, it got me thinking that perhaps our viewpoint on other galaxies is largely influenced by this moment of time and angle of observance. Sure we can say an area of denser matter within a galaxy suggests that we are observing it through a thicker/wider/higher-density area, such as the idea behind the galactic center, but how does that justify a globular galaxy. Perhaps a globular looking galaxy is just a skewed spiral without "density waves". (at this point in time of course)

The same goes for bars. Take a look at this for an example:

whitney music box var. 5 - chromatic - 88 tines

 

Obviously this example is circular rather than elliptical, but you get the idea...

 

Honestly, I haven't read CraigD's post from Scientific American yet, so hopefully it will clear up my confusion about the gases, but I got excited and had to post.

[LaurieAG]

What about you? Do you have an equally logical explanation?

 

Hello Willie,

 

What do you think our solar system would look like from a distance, if we observed several rotations around our 'galactic center' from the same distance away in light years that it took to rotate twice?

 

Possibly something like the attached image (if it had a twin)? Especially if the two systems or 'points' took less time to spin around their common center of gravity than they did around their 'galactic center'.

[WillieB]

In post 12 I concluded that this discussion had reached a natural end. Well, as has been true on occasion before, I was wrong. While waiting for sleep to overtake me last night I asked myself - - - “If the magnetic field produced at the center of the proto-galaxy was self perpetuating, if as more gas joined the accreting mass it was forced to congregate at the poles of the magnetic field (much like the radiation forming our Aurora Borealis), and if this newly added gas created and extended the size and strength of the magnetic field would not this accumulating gas form itself in solid cylindrical shape or, perhaps a thick walled tube?” I concluded that it most probably would. Thus the bar formation became acceptable to me.

 

Then Buffy’s post #4 which introduced the concept of density waves to me led me to study the material authored by Ray Carlberg at Science Questions and Answers: Ask the Experts at Scientific American Magazine dealing with density waves. I am firmly committed to the thought processes that led to the creation of the material to be found at and I believe that all of the peculiarities of our universe will eventually be explainable utilizing the basic characteristics expounded upon in those papers. (Also see the thread “Keep it Simple” posted on this forum) I certainly would not shrink from receiving criticisms and corrections of those characteristics. In fact, such criticisms and suggested corrections and would be more than welcome and I hope that readers of this will be the first to express them. But, at this point, I am attempting to analyze the theorized existence of “density waves” and how they contribute to the formation of spiral galaxies from the perspective of The Incremental Universe.

 

First of all, why do we need the invention of “Density Waves” to explain the development of spiral galaxies? Following Kepler’s Law, the further the expanse of the developing bar retreats from the gravitational center, the longer the circumnavigational period becomes. In the inner regions the gravitational attraction of the material composing the “bar” lying between the outer limit and the gravitational center and the material in the gravitational center itself will exert a “pull” directed almost on a direct line toward the center. Thus the resultant acceleration of the exremities is in that direction. However, as the extremities emerge from this shadow they will feel a pull on a line that no longer passes through the bar but goes directly to the center. Thus the “ends of the bar” will begin to form into a spiral. This would explain why a bar forming or approaching a straight line seems to emanate from a barred spiral galaxy before the spiral formation seems to take effect.

 

As to the “winding problem” which was raised by Eclogite, this would seem to be comparable to the question – “As Pluto’s orbit is so much slower than the inner planets, why hasn’t Pluto spiraled into the Sun?” The Solar System’s orbits are ruled by the same law as the orbits of the stars and detritus which forms the spiral arms of the galaxy. I fail to see the validity of that problem although, I admit, I haven’t done research on its origin.

 

Those galaxies that exhibit multiple arms or other disorders have probably undergone disruptions in the orientation of magnetic fields similar to those that Earth has experienced over the millenniums.

 

I hope that I haven’t presented this in an unacceptably glib fashion. Again, I encourage comments and criticism.

[Buffy]

As to the “winding problem” which was raised by Eclogite, this would seem to be comparable to the question – “As Pluto’s orbit is so much slower than the inner planets, why hasn’t Pluto spiraled into the Sun?” The Solar System’s orbits are ruled by the same law as the orbits of the stars and detritus which forms the spiral arms of the galaxy. I fail to see the validity of that problem although, I admit, I haven’t done research on its origin.

This is actually the crux of the issue at hand: Orbital mechanics dictates that the period of orbit is proportional to the axes of the ellipse of the orbit. What you see in Pluto is that the inner planets orbit many *times* faster, and any "arms" that you trace across the planets would wind up incredibly fast wouldn't they? So stars orbit the galaxy much faster than the arms do--and it does not take much math to figure this out--so they must be density waves.

 

The reason the theory of density waves was even considered was that there was no other logical way to get the arms to move so slowly given what is known about orbital mechanics even in the case of a "billion-body problem": all those body's do act on each other, but there's no way to create the "orbital lock" that would be required to make the stars orbit along with the arms without completely throwing out Kepler and Newton....

 

I have no specific knowledge of electromagnetic fields working at this scale, but I'd think it would be a bit unlikely for them to work at galactic distances...

 

Really big,

Buffy

[WillieB]

Buffy,

 

I especially want to extend my thanks to you. Your posts have been most informative but what I liked most is that they have forced me to think! I have not completely worked out the logic yet, not to mention even attempting to tackle the mathematical aspects, but I am almost positive that I have begun to grasp what may be responsible for the “winding problem.” As I stated before I attempt to solve all unknowns using the principles of the “The Incremental Universe.”

 

Using those principles, gravitational forces are transmitted through an alteration of the velocities of the increments of the free field (and, hence the “retro-velocity” of the paired bundles comprising those increments) while magnetic fields are created by polarization of the orientation of the “flow vectors” of those very same increments. Under these conditions a sufficiently powerful magnetic field will influence the gravitational field in the volume of space in which they co-exist. I am not yet ready to specify the exact nature of this effect or to even begin attempt to tackle the math but rest assured that I will continue to ponder on it. Perhaps you would like to help?

 

If this thought has any validity at all it would seem that sufficiently sensitive experimentation carried out here on our very own planet should be able to verify if this influence or interference actually occurs.