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Here's a published paper that claims that the "maximum disk" model (assumes contant M/L) correctly predicts the rotation curves of 75% of spirals which have extended measured rotation curves withtout a dark matter halo. Another 20% of the galaxies that do not fit the model have substantial bars or arms that reduce the axial symmetry assumed in the model. The paper substantiates the title of this thread.
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Here's a funny one, a paper published in 1942 finds this:
This is long before the modern theory concluded that 80% of mass must be non-baryonic. However it probably also precedes HI measurements of outer rotation.The observed rotational curves of M31 and M33 are found to be adequately represented by a thin-disk models.
Established Member
Papers exist that assert that DM is not needed for rotation curves when you ignore the existence of the halo. Big wow!Originally Posted by TooMany
Here are some of the ~2000 published papers about dark matter and galaxy rotation curves:
A new determination of the local dark matter density from the kinematics of K dwarfs
Disentangling Baryons and Dark Matter in the Spiral Gravitational Lens B1933+503
Haloes gone MAD: The Halo-Finder Comparison Project
Dark and Luminous Matter in THINGS Dwarf Galaxies
Gas and dark matter in the Sculptor group: NGC 300
Established Member
Your statement that I called Kenneth F. Nicholson a crank is insulting. The cranks are C. F. Gallo, James Q. Feng and I listed the evidence that they are cranks (no papers, no citations to their preprints, they are not working astronomers).
You also need to learn to read. There are no Kenneth F. Nicholson papers referenced by these two cranks. What they cite are unpublished, not cited pre-prints by Kenneth F. Nicholson.
Established Member
TooMany, what restricts rocky collisionless DM to galaxy discs
You are not reading your posts carefully or maybe not at all.
You assert that DM is placed in halos because it is collisionless.
You assert that rocky collisionless DM exists.
Conclusion: This rocky collisionless DM has to be placed in the halos.
Thus: TooMany's "proof" that rocky DM is in a spherically symmetric distribution (halo).
You have asserted (not shown) that your rocky collisionless DM is restricted to galaxy discs.
TooMany, what restricts rocky collisionless DM to galaxy discs?
Yes I do.
TooMany, Do you have any training in physics?
P.S.
TooMany, what excludes non-baryonic DM from galaxy halos?
First asked 5 July 2012
Order of Kilopi
Here's a recent astro-ph that TooMany should find particularly interesting: Tidal interaction vs. ram pressure stripping effects as seen in X-rays. Hot gas in group and cluster galaxies.
If Virgo cluster spirals - and these three in particular - have massive, cold, extremely low metallicity, H2-dominated outer disks, what should they look like, when observed as closely, in the x-ray region, as these?
Of course, if the baryonic matter - in the TooManymodelidea - in the outer disks of spirals is in the form of balls of solid hydrogen (with a few extremely low metallicity super-Jupiters thrown in for good measure), then x-ray observations such as these won't say much, will they?
Established Member
Almost quote mining, TooMany
NGC 3741: dark halo profile from the most extended rotation curve
You missed out that this paper also confirms the Burkert dark halo and MOND.The observed rotation curve was decomposed into its stellar, gaseous and dark components. The Burkert dark halo (with a central constant density core) provides very good fits. The dark halo density distribution predicted by the LambdaCDM theory fails to fit the data, unless NGC 3741 is a 2.5-sigma exception to the predicted relation between concentration parameter and virial mass and has at the same time a high value of the virial mass (though poorly constrained) of 10$^{11}$ solar masses. Noticeably, MOND seems to be consistent with the observed rotation curve. Scaling up the contribution of the gaseous disk also gives a good fit.
The Structure and Evolution of Weakly Self-interacting Cold Dark Matter Halos, Andreas Burkert, 2000.
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It really doesn't confirm anything, it just lists possibilities that are consistent with observations which is entirely different. Speaking of the Burkert halo, non-baryonic DM theorist have conjectured many different properties for these halos in an attempt to explain deviations from the halo model they started with. DM theorist can choose the properties of the non-baryonic matter somewhat as they please in order to get a fit. In one of your papers above this conjecture is made for a CDM fit:
That is not a conclusion but an arbitrary suggestion about what happens to the hypothetical halo in order to get a fit. Possibly the authors are simply seeing a disk distribution of mass. Lately there have been many papers written that strive to explain how the very small fraction that is baryonic affects the massive collisionless halo in order to make the theory work. It is ironic that DM theory which generally says there is 5 to 10 times as much non-baryonic mass as baryonic must resort to the concept that the baryons shape the halo in various ways in order to get the theory to match observations.The NFW halo needs to be oblate with a flattening of a/c = 0.33+0.07 -0.05 to be consistent with the radio data. This suggests that baryons are effective at making the halos oblate near the center.
The behavior of baryons is much more constrained by known physics than the hypothetical DM, but it is also so complicated that it is not easily modeled.
There are two different theoretical points of view here. In LCDM, there must be an undiscovered particle that accounts for 5-10 times the baryonic mass in the universe. This matter must be nearly collisionless and the shape of galactic halos must be roughly spherical as a consequence. These assumptions about the non-baryonic matter are necessary to support nucleosynthesis conclusions of Big Bang Theory. Overwhelming the focus in astronomy today is driven by this theory.
On the other hand, an astronomer could also take a purely observational approach and not presume any new type of particle is involved. Looking from that point of view, a question is "can reasonable assumptions about baryonic matter explain the galactic rotation curves". From the papers I have sited above, the answer seems to be yes. It is not necessary to find 5-10 times more baryonic matter than already found to model the galactic rotation curves. So baryonic matter is also a viable solution for these rotation curves and in fact eliminates some standing issues with galaxies using CDM (as already pointed out in Davies paper).
On the other hand, studies of galactic velocity dispersion in clusters indicate that there is much mass that we are not seeing. In fact all we see are galaxies and very hot intergalactic matter (mostly H of course). So here I must agree that either 1) much mass is present that we do not see, 2) some of our assumptions about cluster dynamics are wrong, 3) the Newtonian approximation of GR is incorrect on these scales or 4) GR is wrong at these scales. Quite a few possibilities remain open to explain clusters. It is not conclusive that CDM is the explanation. It may be a more difficult problem to solve than galaxies because the scale is much larger.
All of this is far from settled regardless of what theory you currently prefer. We can only look forward to future observations and analysis to solve the problems. We must keep open minds. Current theory could be wrong.
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Non-baryonic matter is collisionless. As such it must be distributed more of less spherically (given enough time to virialize).
I just explained that in post #263. "Rocks" could not form in random orbits and they did somehow, they would be much more likely to collide than if formed in the disk. Given enough time the collisional debris of baryonic matter would end up in the disk. This is why the disks exist in the first place.
If you don't understand this, what can I do? I'm sorry but I'm tired of trying to explain it to you.
In college, I majored in physics for three years before switching my major to math.
How about you?
Nothing excludes non-baryonic DM from the galaxy halos. It must be spherically distributed if it is collisionless and, if there is lots of it, depending on it's temperature it will form a halo of some size. The same is not true for baryonic matter precisely because it is not collisionless.
Order of Kilopi
I don't follow your reasoning on this (ETA: ...and you haven't expressed your reasoning - just your conclusion). What's "collisionless" have to do with it? If some non-baryonic matter started out distributed like a pancake, what would make it end up in a spherical distribution?
Last edited by Cougar; 2012-Jul-12 at 08:26 PM. Reason: ETA
Everyone is entitled to his own opinion, but not his own facts.
Order of Kilopi
You are improperly misrepresenting the LCDM position. CDM is not assumed to be 5-10 times the baryonic mass in galaxies. The observations of galactic rotation curves require that conclusion. Myriad other scientists and amateurs such as yourself have tried to imagine that there might be a different conclusion to be drawn from these observations. That is not out of the question, but so far, these attempts are obviously not very convincing. And your position - "maybe it's baryons" - is less than not very convincing.
Big bang nucleosynthesis really has nothing to do with these galaxy observations. The fact that that piece of the puzzle fits well with this piece of the puzzle is just confirmation that both pieces appear to be on the right track.
And don't claim that scientists are entrenched in their positions. If that were so, the acceleration of the expansion would not have been embraced by the community so quickly.
Everyone is entitled to his own opinion, but not his own facts.
Established Member
TooMany: do you have any quantitative analysis to present, or are you just link spamming and throwing ideas about? We get that you seem to think you are smarter than astronomers, but you're going to have to do some math if you want your claims to get any traction.
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I don't know. You tell me. BTW, are you an astronomer or physicist by any chance?
From what I've been reading, the dark baryonic matter in spirals doesn't have to be all that massive in order to account for rotation curves.
No they won't. If more baryonic matter exists in such a condensed form, it is not going to be easy to detect, unlike hot or warm gas and dust.
Order of Kilopi
TooMany: in an earlier post, ngc3314 mentioned a widely-read textbook, on the dynamics of galaxies:
Now you said this about yourself, in a post earlier in this thread:
I think parejkoj, among others, has expressed the opinion that (if I may paraphrase) your posts show little concrete evidence that you have mastered the basic physics and maths necessary to hold the kind of informed discussion you seem to be seeking.
If I may, I'd like to recommend that you get a copy of Binney and Tremaine, and work through it, until you are confident that you have grasped the key points. If you did, indeed, major in physics (and then switched to maths), then this book might be pretty heavy going on your own, but if you feel you have, in fact, mastered the physics and maths typically taught to (three-year, full-time) BSc students (majoring in physics), you should be able to do it (though it might take you a year or two).
Of course, there are quite a few good textbooks on topics directly relevant to this thread; for example Physics of the Interstellar and Intergalactic Medium (Bruce Draine), Galactic Astronomy (Binney), and Galaxy Formation and Evolution (Mo). For something a bit less meaty, perhaps you could start with Galaxies in the Universe: An Introduction (Sparke). And maybe other readers could suggest other books too.
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Then you don't know why non-baronic dark matter has a halo distribution.
Let's suppose you had these collisionless DM particles orbiting nicely in a flat disk, kind of like a galactic disk only perfectly flat. Occasionally they will interact with (perturb) one another through gravity. These interactions will disperse their velocity vectors a bit. Some particles will no longer orbit in the thin disk. These particles will interact (gravitationally) with others still in the disk, disturbing their orbits. After a long while, the particles will no longer be in disk-like orbits. The will orbit at angles and the orbits will not be circular. The motions will be somewhat more random. Because the particles are completely collisionless there is nothing to prevent this randomizing process from continuing until the orbits are random. In other words a flat disk of such particles would be completely unstable. Using the virial theorem, a statistical distribution of final velocities can be computed. The average motions will be such that the angular momentum is conserved. But, aside from this average rotation, the particles will no longer have a flat disk distribution. In fact, if the angular momentum of the disk was initially zero, the result will be a spherically symmetric distribution of particles in statistically randomized orbits. Picture a swarm of bees. If you don't believe me, look it up.
It is this analysis of collisionless particles that led astronomers to the conclusion the CDM must exist in more or less spherical halos. The same analysis allows them to predict the density distribution of the halo, which is highest in the center and falls off in a power law. The exact size of the halo you get depends upon the mass and the temperature of the particles. Astronomers prefer cold (slow moving) particles because hot ones could not form dense enough halos to explain how galaxies and large scale structure formed so quickly after the Big Bang.
If the same flat disk of matter is instead baryonic, the gravitational interactions will also disturb the orbits. However, if some of the particles no longer orbit in the disk, they will collide with particles in the disk (because the paths will cross). These collisions make the results completely different. The collisions dissipate some of the velocity (through radiation). Velocities normal to the disk tend to die out from the collisions. Non-circular orbits will also tend to circularize on account of the dissipating collisions. The particles will tend to move in a way that minimizes collisions. Although the particles will no longer orbit in a perfectly flat disk, an equilibrium will be reached in which the disk has some non-zero thickness. In the case of the Milky Way, the baryonic disk is roughly 100 times wider than thick.
Things get more complicated if some of the baryonic matter condenses into balls or planets or stars. The larger the objects that form are, the lower the probability of collision becomes.
You can imagine this process in the formation of the solar system. First there was just a cloud of gas and dust that started to condense. The angular momentum was conserved so the particles moved in orbits about the center of mass. Because they collided, they formed a dusty, gaseous disk. Then, the particles in the disk began to accrete (condense) into larger and larger objects - the sun and the planets. This greatly lowered the probability of collisions. Some of the planets may have interacted gravitational and been ejected. Some may have collided and reformed. The planets may have all been gas giants initially. As the new sun grew hotter, the gaseous envelopes of the inner planets were swept away by solar radiation and the solar wind, leaving only the solid cores (at least this is one theory of the final part of formation). The final configuration has been stable for billions of years, but it is believed that formation time was relatively short.
Collisionless particles have no means of dissipating energy through interactions, but baryonic particles do. They can radiate when they collide with other particles. It is possible however for collisionless particles to interact with baryonic particles through gravity, but this interaction is much weaker than the interaction between baryonic particles through collisions and radiation. Up till some point, most simulations of CDM structure formation ignored the baryonic matter because 1) it comprises a small part of the overall mass in the theory and 2) it greatly complicates the analysis. But lately, theorists have been appealing to the power of the baryonic matter to disturb the non-baryonic halos in order to explain some problems with the theory not matching observations of galaxies. Also, within limits, CDM theory apparently allows some choices in the exact properties of the non-baryonic matter. This flexibility has also been used to explain various problems. I've seen proposals for warm dark matter, slightly collisional dark matter, sticky dark matter and even mixes of different temperatures and/or types of dark matter.
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That's not quite correct. The observations require that much mass to explain the rotation curves if additional mass is non-baryonic, i.e. collisionless. The same amount of mass is not required in a disk distribution of dark baryonic matter.
I'm not trying to convince anyone that it is baryons. I don't know! I'm just saying that it is very important to test that possibility. Insisting that there must be a super large amount hidden mass, doesn't help eliminate the possibility of a smaller amount of hidden baryons. As some of the papers I cited above indicate, we need to analyze what we know about galaxies from observations and attempt to also explain this behavior within invoking a particle that has never been detected. The possibility should not be ignored simply because we think a certain theory is right.
It is closely related to the explanation for these galaxy observations however. The Big Bang nucleosynthesis theory predicts how much baryonic matter is required in order to match the primordial abundances of elements. However, this does not provide enough mass to explain a number of things. To maintain the nucleosynthesis prediction as correct, any additional mass must be something that does not interact with baryonic matter.
That is an interesting point. Somebody recently cited a paper that suggested a possible acceleration, prior to the SN 1a discovery. Once inflation was accepted as an explanation for the uniformity of CMB, it was much easier to accept an unexplained acceleration. The paper argued that if we accept inflation, then why not also a cosmological constant as Einstein had once proposed. The paper suggested a search for evidence of a cosmological constant but did make any particular prediction. Inflation after all is a phenomenal unexplained universal acceleration with a very finite duration.
Recently a paper raised the serious possibility that there is no acceleration, but rather a distortion caused a locally lower mass density (z<0.1). Of course it's not conclusive.
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If you want some quantitative analysis of rotation curves, I suggest you read the papers that I have cited. I'm am not personally competent to do the calculations.
My only claim is that we have not exhausted the possibility that galactic rotation curves are a result of baryonic matter. Quite a few papers have expressed this possibility. It is still on the table (IMO). The big problem with this possibility is that it would not support the rest of the existing theory so we would have to start scratching our heads again.
I don't think I'm smarter. These are very smart and clever people. They have built a theory that is very popular among them because it explains some things. What bothers me is that the theory rests on certain hypothesis that have not been substantiated. Inflation is a conjecture which cannot be falsified. As such it is not observational evidence. It is not scientific evidence. It is purely a hypothesis that explains how the CMB we observe can be the result of the Big Band. There is considerable evidence for DM. However the conjecture that DM comprises 85% percent of all mass but consists of particles never detected is also profound. This conjecture cannot easily be falsified. It's been 40 years but no direct detection has occurred. That's not to say that it won't be found, but how long should we wait? Should we not explore other possibilities because we believe this must be the right one?
How about looking at another theory called Supersymmetry in particle physics. There are very good theoretical reasons for proposing this theory. Very smart physicists have called the theory beautiful. The theory has been around, taught and developed for 30 years now. However the LHC experiments have already eliminated the most popular forms of the theory. It is still possible that something will turn up, but it will not be exactly what most physicists expected.
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I really consider that a direct insult, Nereid. Would you care to show specifically where I have failed to demonstrate an understanding of basic physics and math?
What exactly are your credentials? I asked you before after I told you what my educational background is but you did not answer.
Established Member
Incomplete: Any matter that is collisionless must be distributed more or less spherically (given enough time to virialize).
No you did not. You made an series of assertions without any citations or calculations.
Discs basically exist because of the conservation of angular momentum: Formation of disk galaxies
7 years of university finishing with an M.Sc. (solid state physics).
And once again: Your rocky DM is either collisionless (and so must be spherically distributed) or collides (and so is hot, easily detected dust)!
You can get around this by making up a fairy story though.
Once upon a time, magic happened and rocks formed in the halo without the need for stars. This magic was very special beause it only happened in the halo, not in the rest of the galaxy such as the central bulge. They formed in random, elliptical orbits. There were about 10,000,000,00 of these rocks per star in the rest of the galaxy if they were Pluto sized. Then the wizard called Collision made the orbits of these rocks change the orientation and shape of their orbits so that they were in the disc and circular. This destroyed the wizard!
Established Member
Think about what happens if you replace collisionless DM particles or rocks with stars which are also collisionless. Then over the long term you have the disc vanishing!
In the short term you have a population of halo stars that have migrated from the dic. But stars in the halo are old: Galactic spheroid
Unlike the galactic disc, the halo seems to be free of dust, and in further contrast, stars in the galactic halo are of Population II, much older and with much lower metallicity than their Population I cousins in the galactic disc (but similar to those in the galactic bulge). The galactic halo also contains many globular clusters.
Established Member
You need to learn what inflation is. It is a scientific theory which can be falsified. It fitted observations (the universe may be flat, monopoles have not been observed, the universe appeared homogeneous and isotropic). It makes falsifiable predictions. Predictions have been verified by WMAP and that monopoles still have not been observed.
Your conjecture that "DM comprises 85% percent of all mass but consists of particles never detected is also profound" is profoundly wrong.
The fact that we have not detected DM particles is trivial. How many years did we look for the Higgs particlShouldoud we have stopped after 1 year,yearsars, 10 years or 39 years after it was proposed?
Scientists will continue to look for DM particles so long as there is evidence (as you have been told about repeatably - LSS, WMAP, etc.) that DM particles exist.
Established Member
We don't "scratch our heads" (well, ok, sometimes we do...). We develop quantitative models and test them against observations. That's what astronomy is. It's not "oh, I have a great idea that you've all missed and you should listen to me even though I haven't worked out any of the details, plus I'm just going to post about it on some forum on the internet". Whether you think that's what you're saying, it is how you are coming across. If you want people to care about your ideas, you have to present them quantitatively (humbly doesn't hurt either). I've even given you some suggestions about how you might go about doing so.
Seriously, what's your goal with these threads? I've already told you that there are--when this was BAUT: there may be more since the cosmoquest merge--fewer than 10 practicing astronomers/physicists who participate in these threads, and even they aren't going to write a paper based on the random musings of some forum poster. At least three (maybe more) of them have directly responded to you, often with the suggestion that you should start with some basic textbooks. Jumping from paper to paper speculating on what they mean independently of anything else isn't going to help you, or anyone else, learn anything.
The funny thing of it is, if you go up to most astronomers and tell them "we have not exhausted the possibility that galactic rotation curves are a result of baryonic matter," they'll say "Sure, what's your point?" Banging on about this, without presenting a coherent model that also explains most of our other observations is just making a pest of yourself. We've tried lots of other models, but none do as well as the current concordance cosmology when you consider the preponderance of the evidence. You're welcome to dislike it (I can name a good number of astrophysicists who do!), but disliking it doesn't make it less correct, and disliking it without any quantitative reason to do so strikes me as particularly frivolous.
Moderator
Okay, I think this has gone round in circles long enough.
If you are not competent to do the calculations, how can you claim that those who are competent to do the calculations are not doing their job correctly.
Just your feeling something might not be okay or incomplete is not enough.
Thread closed.
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