What is the newly discovered explanation for the evolution of spiral galaxies?

[Charles Franc]

Spiral galaxies are among the most beautiful and familiar objects in the heavens, but a working explanation as to why galaxies evolve into spirals has eluded astronomers for decades. Now, two independent researchers have published a compelling solution to this eighty year old problem, which appears in the November 2009 issue of Proceedings of the Royal Society A. Consequently, the Milky Way must be remapped. This newly emerging picture of our galaxy is being released online today as a high‐resolution digital image. The Milky Way is revealed as tightly wound “grand design” two‐armed spiral – not a four‐armed spiral as has previously been supposed.

Download the new map of the Milky Way @ http://astrostudio.org/milkyway.html

Independent mathematician Charles Francis of Hastings, U.K., and amateur astronomer Erik Anderson of Ashland, Oregon, had been working on a quite different problem when the discovery was made. Anderson had compiled data from existing sky surveys on more than 20,000 Milky Way stars with accurately known positions and velocities. By treating orbits as precessing ellipses, Francis found that mutual gravitation naturally leads to orbital alignments that generate spiral patterns. Orbital motions follow spiral arms over large distances.

Watch an animation of the galaxy in motion @ http://rqgravity.net/SpiralStructure

Francis likens the gravitational potential of a spiral galaxy to a giant funnel with spiral grooves. Stars, like rolling marbles, are channeled along the grooves until they build enough momentum to escape. Escaping stars migrate away from the galactic center, crossing over the next highest groove, and falling back into the same groove they came from.

See the spiral funnel diagram @ http://rqgravity.net/images/spiralmotions/funnel2.gif

Francis and Anderson’s model also explains why spiral patterns are stable. As an arm accumulates stars, its gravitational field grows stronger, making its “groove” deeper and drawing greater numbers of stars into it. Thus, mutual gravity between stars reinforces spiral structure. The gravity of the arms locks the rate of orbital precession to spiral pattern speed (which rotates slowly backwards) for a wide range of orbits. Interstellar gas, following similar motions, also contributes to the formation of “grand
design” two‐armed spirals.

“The idea is so simple that I had initially rejected it,” Francis confesses. “I thought that if it were right, it would already be known; but when I compared it to data, it worked straight away, giving a perfect fit.”

Astronomer Rainer Klement, at the Max Planck Institute for Astronomy in Heidelberg, Germany, agrees. “It is a very nice paper with very good ideas and explanations for the kinematic structures we observe,” Klement remarks. “It comes up with an elegant way of explaining the velocity distribution in the solar neighborhood.” Klement believes that future observations, covering even broader regions of the galaxy with even greater precision, will support the paper’s conclusions.

The introduction of a working model for spiral galaxies will revolutionize the study of galactic dynamics. “It comes as a surprise to most people that galactic orbits of stars are still treated in textbooks using a model of epicycles introduced in the 1920s,” Francis notes. “Epicycles are generally believed to have been banished from astronomy over three hundred years ago, when Newton explained Kepler's discovery that planetary orbits are ellipses. In popular culture, ‘adding epicycles’ refers to the process of introducing fudges to make a theory fit data, when actually the theory needs to be replaced in its entirety.”

Learn about epicycles in modern astrophysics @ http://rqgravity.net/PtolemyIsDead

Francis and Anderson’s peer-reviewed paper, “Galactic spiral structure,” appears online @
http://rspa.royalsocietypublishing.org/content/465/2111/3425

--

 

[Chronos]

Recent research results suggest the milky way is a barred spiral.

 

[Charles Franc]

Indeed. The artist's impression shows a barred spiral. If you look at images of barred spirals you will find the bar can take a number of forms. The artists impression shows one of those forms.

 

[marcus]

As I recall, in another thread you identified yourself as Charles Francis. Correct me if I am wrong but from what you say I suppose I can address you as the author of this paper with Erik Anderson.
http://arxiv.org/abs/0901.3503
Galactic Spiral Structure
Charles Francis, Erik Anderson
(Submitted on 22 Jan 2009 (v1), last revised 31 Aug 2009 (this version, v3))

"We describe the structure and composition of six major stellar streams in a population of 20 574 local stars in the New Hipparcos Reduction with known radial velocities. We find that, once fast moving stars are excluded, almost all stars belong to one of these streams. The results of our investigation have lead us to re-examine the hydrogen maps of the Milky Way, from which we identify the possibility of a symmetric two-armed spiral with half the conventionally accepted pitch angle. We describe a model of spiral arm motions which matches the observed velocities and composition of the six major streams, as well as the observed velocities of the Hyades and Praesepe clusters at the extreme of the Hyades stream. We model stellar orbits as perturbed ellipses aligned at a focus in coordinates rotating at the rate of precession of apocentre. Stars join a spiral arm just before apocentre, follow the arm for more than half an orbit, and leave the arm soon after pericentre. Spiral pattern speed equals the mean rate of precession of apocentre. Spiral arms are shown to be stable configurations of stellar orbits, up to the formation of a bar and/or ring. Pitch angle is directly related to the distribution of orbital eccentricities in a given spiral galaxy. We show how spiral galaxies can evolve to form bars and rings. We show that orbits of gas clouds are stable only in bisymmetric spirals. We conclude that spiral galaxies evolve toward grand design two-armed spirals. We infer from the velocity distributions that the Milky Way evolved into this form about 9 Gyrs ago."

Comments: Published in Proc Roy Soc A.
A high resolution version of this file can be downloaded from [ http://papers.rqgravity.net/SpiralStructure.pdf ]
A simplified account with animations begins at [ http://rqgravity.net/SpiralStructure ]
====
I went to the second URL and checked out the animation, which gives an intuitive sense of how your idea works----how you think spiral arm structure can form and persist. The first URL did not work for me----that is the one that says SpiralStructure.pdf.

I was a little confused by your referring to yourself in the third person in the above post. I don't moderate or have any mentor role but my personal thought is that there is no reason for you to be shy. Your work, in this case, was peer-reviewed and accepted for publication in the Proceedings of the Royal Society. You describe yourself as an independent mathematician and Erik Anderson as an amateur astronomer. Independents and amateurs have contributed to science in the past (very significantly) and doubtless will continue to do so. The important thing is you passed peer-review.

To whatever extent I can welcome you, welcome to PF's astronomy section. I hope you get some reaction and discussion from us of your reviewed and published results!

 

[marcus]

I see that you and Anderson have also recently published an article in New Astronomy

Francis C., Anderson E. 2009 Calculation of the local standard of rest from 20 574 local stars in the new Hipparcos reduction with known radial velocities. New Astron. 14, 615–629.

I also see that the full text of your "Spiral Structure" article is available free at the Proceedings of the Royal Society.
http://rspa.royalsocietypublishing.org/content/465/2111/3425.full
So one doesn't merely get the abstract at that site. One gets the whole works, with lots of graphics as well.

For some reason I had the notion that Frank Shu, an old teacher of mine, had explained spiral structure quite some time ago.
Or perhaps he just participated in developing and presenting a theory of spiral structure. The term "density wave" comes to mind, but that may be wrong. I don't see a reference to Frank Shu in your paper. If anyone is curious here's the wikipedia:
http://en.wikipedia.org/wiki/Frank_Shu

Do you have a reference to some of the leading explanations from way back? Like the 1980s? It bothers me that your post refers to this as a problem that was "unsolved for 80 years" until you and Anderson came along. I would be more comfortable thinking of it as one of several proposed models, a respectable contender. But I am reluctant to think of it as the first ever solution, or as conclusively correct. However you may be right and it may be! I don't have any expert knowledge about spiral structure.

 

[turbo]

You describe yourself as an independent mathematician and Erik Anderson as an amateur astronomer. Independents and amateurs have contributed to science in the past (very significantly) and doubtless will continue to do so. The important thing is you passed peer-review.

To whatever extent I can welcome you, welcome to PF's astronomy section. I hope you get some reaction and discussion from us of your reviewed and published results!

Welcome Charles, and as Marcus said, don't be shy. Some of us research things we are passionate about, and are willing to put in years of grunt-work to assemble data, ruthlessly self-critique the findings, and to put the findings in a form that is worthy of publication in a prominent peer-reviewed journal. After having been through that (and presently developing a second in what promises to be a long chain of papers) I applaud your efforts.

If it gives you any solace, my collaborators are college graduates, and I am not, though I am the lead author on the upcoming paper. Not an advanced degree among us, unless my partners are holding out. A prominent observational astronomer/astrophysicist told us at the outset of the initial project that we were nuts to take on the challenge, though he encouraged us to continue. We had no university affiliation or funding and no grad-students or post-docs to enslave for such a labor-intensive project. Lucky for us, we stayed "nuts" and just ground it out.

Astronomy is necessarily an observational science, and it is refreshing to see research that starts with "This is what we see. Can we derive a model that explains it?" The study of formation of structure in our universe needs to get such an epistemological gut-check a lot more frequently IMHO.

Again, welcome. I have no standing on this forum, but am an enthusiastic proponent.

 

[Charles Franc]

For some reason I had the notion that Frank Shu, an old teacher of mine, had explained spiral structure quite some time ago.
Or perhaps he just participated in developing and presenting a theory of spiral structure. The term "density wave" comes to mind, but that may be wrong. I don't see a reference to Frank Shu in your paper. If anyone is curious here's the wikipedia:
http://en.wikipedia.org/wiki/Frank_Shu

Do you have a reference to some of the leading explanations from way back? Like the 1980s? It bothers me that your post refers to this as a problem that was "unsolved for 80 years" until you and Anderson came along. I would be more comfortable thinking of it as one of several proposed models, a respectable contender. But I am reluctant to think of it as the first ever solution, or as conclusively correct. However you may be right and it may be! I don't have any expert knowledge about spiral structure.

I am Charles Francis. There was a blip when I entered my name in physics forums. As far as I can tell there is no way to change it. The use of third person was because I posted text from a press release - sorry, it just seemed unnecessary work to rewrite it. I'm generally not at all shy, and I am moderator on sci.physics.foundations.

You're right about Frank Shu and density wave theory. I hadn't realized but the ref in the paper is to Lin et al.. Shu is the third author. I probably should also have reffed Lin & Shu's 1964 paper. Density wave theory is usually called a hypothesis. It was originated by Lindblad. Lin & Shu, and later Kalnajs, bolstered it with some rather dubious mathematics. Actually it doesn't hold together very well. I have been somewhat critical on one of my web pages. http://rqgravity.net/PtolemyIsDead

One should remember that these older hypotheses (there are others) were formed before there was anything very much in the way of useful data. I think the structure we have described can be regarded as proven by comparison with data, and also by numerical analysis from the laws of Newtonian Gravity. This is of course the subject of the paper. Regarding proof, there is also important stuff in the electronic appendix. The website has a simplified analysis, spread over four pages which can be reffed from http://rqgravity.net/SpiralArms

 

[Charles Franc]

Welcome Charles, and as Marcus said, don't be shy. Some of us research things we are passionate about, and are willing to put in years of grunt-work to assemble data, ruthlessly self-critique the findings, and to put the findings in a form that is worthy of publication in a prominent peer-reviewed journal. After having been through that (and presently developing a second in what promises to be a long chain of papers) I applaud your efforts.

If it gives you any solace, my collaborators are college graduates, and I am not, though I am the lead author on the upcoming paper. Not an advanced degree among us, unless my partners are holding out. A prominent observational astronomer/astrophysicist told us at the outset of the initial project that we were nuts, though he encouraged us to continue. We had no university affiliation or funding and no grad-students or post-docs to enslave for such a labor-intensive project. Lucky for us, we stayed "nuts" and just ground it out.

Astronomy is necessarily an observational science, and it is refreshing to see research that starts with "This is what we see. Can we derive a model that explains it?" The study of formation of structure in our universe needs to get such an epistemological gut-check a lot more frequently IMHO.

Again, welcome. I have no standing on this forum, but am an enthusiastic proponent.

Thanks for the welcome, and thanks also to Marcus. I do have a Ph.D. (maths, on quantum electrodynamics - a long way removed from this), but Erik has no degree, and I will say that I couldn't have done it without him. Actually there has been much more grind on far more difficult papers which we can't get published (see physics forums>Independent Research - would those be interesting papersto discuss here?). There was also much more grind on the first paper in New Astronomy. Of course we couldn't have done the Spiral Arms paper if we hadn't put in the hard work in analysing the data first, but once I tried the mechanism everything fell together in about a month, and I suddenly knew I could explain all the patterns we had been seeing, so it seemed really easy.

 

[Chronos]

You are more than welcome to post in the independent research forum. That is what it is there for. Hopefully you will get quality input there with less noise to signal ratio. The denizens there are very math savvy so you need not dumb it down. Judging by the quality of your papers thus far, this should not be a concern.