The case for [or against] dark matter

[Chronos]

This paper, http://arxiv.org/abs/1507.06282, The Duhem-Quine thesis and the dark matter problem, may be of interest to those curious about how and why dark matter has gained general acceptance by cosmologists

 

[betzalel]

After more than 50 years the direct search for dark matter has been negative which would make sense if dark matter does not exist.

http://www.popsci.com/article/science/inside-hunt-dark-matter

“I’ve been looking for dark matter for 23, no, 24 years now,” he says. And he is not alone; the search for dark matter has grown into a small industry, albeit one that does not yet have a product to sell. “Every experiment has reported essentially negative results. No one even knows for sure if the damn stuff really exists. Those fellows,” Gaitskell says, nodding to the pit, “know exactly where the gold is.” I realize now he is not feeling empathy for the miners. He is feeling envy."There more than a dozen separate astronomical observations that cannot be explained by the dark matter hypothesis and cannot be explained by a change in gravity. Complex holistic problems cannot be solved by guessing. It appears there are sufficient observations to solve the cosmological puzzles which is more complicate that is there or there not dark matter.

There are close to a hundred significant astronomical anomalies and paradoxes, including structural anomalies, that indicate there are fundamental errors in the standard cosmological model, at the most basic level.

An incorrect theory will generate paradoxes. If a theory is incorrect at a fundamental level, it blocks all progress.

The standard approach when there are piles and piles of anomalies and paradoxes in a field, is to separate the observations from the theories and to start from square one using the observations to lead, to construct alternative theories. Comment:
An example of a structural anomaly is in geology were there were many observations that indicated the continents had separated and that the continents moved. The solution to the geological anomalies has a new mechanism, continental drift. http://www.eso.org/public/news/eso1217/"Serious Blow to Dark Matter Theories?
The most accurate study so far of the motions of stars in the Milky Way has found no evidence for dark matter in a large volume around the Sun. According to widely accepted theories, the solar neighbourhood was expected to be filled with dark matter, a mysterious invisible substance that can only be detected indirectly by the gravitational force it exerts. But a new study by a team of astronomers in Chile has found that these theories just do not fit the observational facts. This may mean that attempts to directly detect dark matter particles on Earth are unlikely to be successful.

A team using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory, along with other telescopes, has mapped the motions of more than 400 stars up to 13 000 light-years from the Sun. From this new data they have calculated the mass of material in the vicinity of the Sun, in a volume four times larger than ever considered before.

“The amount of mass that we derive matches very well with what we see — stars, dust and gas — in the region around the Sun,” says team leader Christian Moni Bidin (Departamento de Astronomía, Universidad de Concepción, Chile). “But this leaves no room for the extra material — dark matter — that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there!”http://www.scilogs.eu/en/blog/the-dark-matter-crisis/2012-04-19/dark-matter-gone-missing-in-many-places-a-crisis-of-modern-physics[/URL]

[URL]http://arxiv.org/pdf/1204.3377v1.pdf[/URL]

[B] "Dark Matter is missing in the Local Universe[/B]

In the work titled “[URL='http://arxiv.org/abs/1204.3377'][U]Missing Dark Matter in the Local Universe[/U][/URL]”, Igor D. Karachentsev has looked at a sample of 11,000 galaxies in the local Universe around the MW. He has summed up the masses of individual galaxies and galaxy-groups and used this to test a very fundamental prediction of LCDM.

The idea is as simple as it is brilliant: cosmology has precise predictions as to what is the content of our universe. In particular, it predicts the density of matter to be Ωm,glob = 0.28 +- 0.03 (83 per cent of this in dark, 17 per cent in luminous matter). Now, to test this, all you have to do is to sum up all the mass within a certain volume of space, and you can estimate the actual density of mass within that volume. To be sure that your volume is representative, it needs to be large. If you only sum over, say, a sphere of 100 kpc in diameter, the density strongly depends on whether you have a galaxy in this volume or not. Karachentsev chose to use a volume with a radius of 50 Mpc around the MW. On this size-scale, the density is expected to fluctuate by only 10 percent, a reasonably low value in astronomy. The scale can thus be assumed to be representative and you should observe the mass density predicted by LCDM.

Except that you do not.

Karachentsev reports that the average mass density is only Ωm,loc = 0.08 +- 0.02, a factor of 3-4 lower than predicted and can not be explained by the uncertainties in the data or prediction. As most of the mass-content in the Universe is supposed to be dark matter, this means that most dark matter is missing in this volume."Normal matter interacts gravitational with “dark matter”, so dark matter can loss or gain energy from the galaxy. Unfortunately for the “dark matter theory”, hydro-dynamic simulations, fundamentally disagree with real galaxies. The simulations create a model disc that is an order of magnitude smaller than what is observed. This discovery, which is called the “angular momentum catastrophe”, was made 8 years ago. There is no solution to the angular momentum catastrophe, which is not surprising; however, as more detail data and observations concerning spiral galaxies shows structures that could not possibly have been created by the interaction of “dark matter” and normal matter.

It should be noted that the ‘angular momentum catastrophe” problem and the “missing satellites problem” is leading some researchers to state that dark matter does not exist which is interesting as LCDM theory will need to change. The “angular momentum catastrophe” and the missing satellites problem” are not the only fundamental disagreements with the “dark matter” theory and reality.

This is an example of an anomalous observation that indicates galaxies do not form from mergers and stray gas clouds. How galaxies do form explains the angular momentum anomaly and the velocity anomalies.

[URL]http://www.sciencedaily.com/releases/2014/07/140721100418.htm[/URL]

[B]"Mysterious dance of dwarf galaxies may force a cosmic rethink[/B]
The discovery that many small galaxies throughout the universe do not 'swarm' around larger ones like bees do but 'dance' in orderly disc-shaped orbits is a challenge to our understanding of how the universe formed and evolved. The researchers believe the answer may be hidden in some currently unknown physical process that governs how gas flows in the universe, although, as yet, there is no obvious mechanism that can guide dwarf galaxies into narrow planes."[URL]http://www.nature.com/nature/journal/v511/n7511/full/nature13481.html[/URL]

"Velocity anti-correlation of diametrically opposed galaxy satellites in the low-redshift Universe

Recent work has shown that the Milky Way and the Andromeda galaxies both possesses the unexpected property that their dwarf satellite galaxies are aligned in thin and kinematically coherent planar structures1, 2, 3, 4, 5, 6, 7. It is interesting to evaluate the incidence of such planar structures in the larger galactic population, because the Local Group may not be a representative environment. Here we report measurements of the velocities of pairs of diametrically opposed satellite galaxies. In the local Universe (redshift z < 0.05), we find that satellite pairs out to a distance of 150 kiloparsecs from the galactic centre are preferentially anti-correlated in their velocities (99.994 per cent confidence level), and that the distribution of galaxies in the larger-scale environment (out to distances of about 2 megaparsecs) is strongly clumped along the axis joining the inner satellite pair (>7σ confidence). This may indicate that planes of co-rotating satellites, similar to those seen around the Andromeda galaxy, are ubiquitous, and their coherent motion suggests that they represent a substantial repository of angular momentum on scales of about 100 kiloparsecs."

 

[Chronos]

I have little faith in popsci presentations - I view they have too many publishing agendas to satisy to be unbiased and reliable. If you choose to appeal to peer reviewed papers, please clarify which ponts you find interesting. A smorgasborg of dissenting papers on dark matter is unsatisfying. They are as common as UFO sightingts.

 

[betzalel]

Summary:

The observations do not support the assertion that there is dark matter and do not support the assertion that general relativity (gravity) is incorrect. It is a fact that there are multiple galaxy anomalies that requires an explanation. The list of galaxy anomalies is growing year by year.

It seems that it is time to move on and to start the search for alternatives. This area of cosmology (galaxy formation and evolution) should be in a crisis which a good thing, a normal step in fields of science if the objective is to solve a problem, rather than to talk endless about incorrect toy models which accomplishes nothing.

The below list is a sample of the observations that support the assertion that it is very, very, likely that dark matter does not exist.

1) Direct dark matter detection, negative after 50 years search. One cannot find what does not exist. If dark matter does not exist there is no progress until other solutions are looked for. The solution is not changing gravity. When there are multiple fundamental observations that do not support a theory, it is better to have no theory rather than an incorrect toy theory which blocks all progress.

It is a big deal to create a new particle or whatever that does not exist. There are negative consequences for both cosmology and for fundamental physics, if dark matter does not exist and we have spent 50 years before looking for other explanations.

The point is there does appear to be fundamental physics issues, something that will advance fundamental physics with the correct solution to a very long list of galaxy formation and evolution anomalies.

2) Solar system area search for dark matter, negative for dark matter.

3) Local universe search for dark matter, negative for dark matter.

4) Observed spiral galaxy central form, does not agree with simulations for galaxy formation/evolution with dark matter. Cusp problem.

5) Satellite galaxy crisis. There are two few satellite galaxies (there should based on simulations be many hundreds of satellite galaxies rather than roughly 30 in the Milky Way and Andromeda). It has been found in the last five years, that the satellite galaxies that are observed in multiple galaxies (including the Milky Way and Andromeda) are located in a narrow plane. The narrow plane of satellite galaxies cannot be explained by the dark matter mechanism or by galaxy formation by mergers. The initial reaction to finding a plane of satellite galaxies for the Milky Way and Andromeda was to appeal to a weird interaction of the two galaxies, although there was no observational evidence for that assertion. The finding that a plane of satellite galaxies based on observations appears to be ubiquitous for all spiral galaxies, (>7σ confidence), published in Nature, is a big deal.

i.e. Galaxy growth by mergers should produce a sphere of satellite galaxies not a narrow plane of satellite galaxies. There are two anomalies.

1)There are multiple observations that support the assertion that something physical is stopping mergers. i.e. Mergers should produce a sphere of satellite galaxies. If mergers were common then there would be spheres of satellite galaxies. No sphere of satellite galaxies supports the assertion that something physical is stopping/inhibiting mergers.

2) Secondly what is creating the plane of satellite galaxies?

 

[Chronos]

1. The search continues. Negative results tend to motivate more ingenious search methods.
2 Given we don't know what it is we are seeking, that result is unsurprising, You rarely find chicken on the beef counter
3. See above
4. Speculation - how many 'spiral galaxy central forms' do we have for comparison?
5. Our count of satellite galaxies is obviously incomplete, given we keep discovering new ones every year.
6. Objection. The presumed plane of satellite galaxie is inadequately supported by facts in evidence - see 5. The obvious question is how many spiral galaxies are there for which we have a reliable count of satellite galaxies?

 

[betzalel]

It is interesting to first study and try to understand/document the implications of key new and old forgotten anomalous observations (this step is not part of the current cosmological theory paradigm, there are now extraordinarily complete, highly developed, astronomical observations/analysis to work with) and then just for fun try to formulate a high level solution to the problems. No wild guesses, but play with all theoretical assumptions in your own sandbox. The observations are the guide to the correct solution.

As noted a structural anomaly is different than an anomaly that simply cannot be explain by a theory, in this case the theoretical entity 'dark matter'. The implications of the anomalous galaxy observations (there are now dozens and dozens of anomalous observations, I have picked a couple and will add a few more that are easiest to explain to a general audience and that point to the correct solution) is deeper than they falsify the dark matter hypothesis. Changing general relativity (law of gravity) also will not explain the observations. The choice should not be two incorrect hypotheses. No answer is better than an incorrect answer, as that forces/enables/allows people to look at the observations to look for an answer that is at least on the correct page.

The finding of a structural anomaly requires a new mechanism to explain, rather than a rework of the dark matter hypothesis and/or galaxy model simulations. The spiral galaxy observations support the assertion that some of the most basic assumptions concerning how spiral galaxies grow and evolve are incorrect.

The following paper notes the astonishing discovery (this was most certainly not expected) that six spiral galaxy parameters are tightly controlled which is not possible for a dark matter hierarchical galaxy formation theory/mechanism The galaxy parameters in question should be random and highly hence highly variable, not tightly controlled.

The paradoxical implications of this discovery is most easily seen by comparing how observed spiral galaxy angular momentum for different spiral galaxy masses compares to theoretical angular momentum for different spiral galaxy masses.

Spiral galaxy angular momentum was long ago hypothesized to originate from gas cloud torque when the galaxy initially formed. Based on this mechanism, as noted below, the galaxy angular momentum should be random, primarily determined by random circumstances (gas cloud torque) when the galaxy formed and hence should be completely independent of galaxy mass. (i.e. The spiral galaxy would gain mass in the future via mergers maintaining roughly its initial angular velocity as it grows).

What is observed is spiral galaxies have more angular momentum directly proportional to their mass. The implication of this finding is that spiral galaxies mysteriously gain angular momentum as they grow in mass. This is a Goldlock's type problem. Not too much or too little angular momentum. Think of random mergers and the conservation of angular momentum.

There are three questions/anomalies:

1) As noted, there must be some mechanism that stops/inhibits the merger of spiral galaxies. Wet mergers (random mergers of two spiral galaxies with stars) will gradually change spiral galaxies into elliptical galaxies or elliptical like galaxies and will produce random sized galaxy bulges. That is not observed. Wet mergers will most definitely not cause the angular momentum of a galaxy to increase in direct proportion to the spiral galaxy's mass.

What is observed is that spiral galaxies show a continual tightly controlled spectrum of growth with a bulge that grows in direct proportion to the mass of the super large object in the center of almost all galaxies.

What that indicates is the grow of the spiral galaxy is somehow connected with the grow of the super massive object at the center of almost all galaxies.

2) If spiral galaxies do not grow by wet mergers, how then do they grow?

3) How do spiral galaxies gain angular momentum in direct proportion to their mass?

http://www.nature.com/nature/journal/v455/n7216/abs/nature07366.html

http://arxiv.org/ftp/arxiv/papers/0811/0811.1554.pdf

"Galaxies appear simpler than expected

Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment, and feedback from supernova explosions and supermassive black holes1. The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter2,3,4. The properties of an individual galaxy should be controlled by six independent parameters including mass, angular-momentum, baryon-fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free of optical selection effects5, shows five independent correlations among six independent observables, despite having a ...

... This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our dataset. Such a degree of organization appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter paradigm in cosmology6.

...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey."

 

[Lord Crc]

After more than 50 years the direct search for dark matter has been negative which would make sense if dark matter does not exist.

Well it took about 50 years to find the Higgs boson, and we knew what to look for there...

 

[rootone]

'Dark matter' is just a name for an unknown 'something' which evidently exists, because it has observable interactions gravitationally.
It doesn't interact with other fundamental forces, but it is called 'matter' because everything else we know of which interacts gravitationally has mass.
We don't know what it is, we have some ideas and clues, but it definitely is 'something' which exists.

Personally I haven't given up on the idea of MACHO's - we really don't have much clue about how many 'failed' brown dwarf protostars are out there or 'dark' solar systems which our present technology is unable to see. Primordial micro black holes can't be ruled out either.

 

[betzalel]

Of course it is not how long one looks for something but rather has the search determined that it is very, very likely that what one is searching for does not exist.It is bad thing rather than a good thing if cosmology theory advancement has been on hold for 50 years while people search for dark matter and dark energy and attempt to build theoretical models using dark matter and dark energy to attempt to explain galaxy morphology and evolution, if it is a fact that dark matter and dark energy do not exist.

It is important to be able to recognize when the parrot is dead.

John Horgan in his book "The end of science" created the term 'ironic' science to describe sciency work (string theory and cosmology) that may have no basis in reality. Ironic science looks like science and can go on forever, but will never converge on the truth if it is a fact that it concerns theoretical entities that have no basis in reality.

There are more string 'theories' than there are atoms in the universe. There is no definition as of yet as to what is or is not a string. There is as of yet no string 'theory' in that someone has created a mathematical model that makes predictions, that is a 'theory'. String theory is the term used to describe those how create and discuss mathematical models (more than 100,000 string 'theory' papers have been written, very productive field of work if the objective is to write and discuss 'papers') that might one day be a theory.

String 'theory' appears to be very, very, advanced alchemy. The other more traditional approach to solving scientific problems is to look at the observations as a guide to the correct 'theory'. The mathematical model follows that step, rather than leads that step.

The medieval 'alchemy' is an example of primitive ironic science. If dark matter and dark energy do not exist, that is advanced ironic science.

The point is it time to relook at the entire cosmological problem as it is a fact that there are more and more anomalies concerning every aspect of the standard cosmological theory components due to multi spectrum data at all redshifts.The Frenk Principle:

"If the Cold Dark Matter Model does not agree with observations, there must be physical processes, no matter how bizarre or unlikely, that can explain the discrepancy."The Strong Frenk Principle: (2 versions)

1: "The physical processes must be the most bizarre and unlikely..."

2: "If we are incapable of finding any physical processes to explain the discrepancy between CDM models and observations, then observations are wrong."

- George Efstathiouhttps://www.astro.umd.edu/~ssm/mond/DMOct05.pdf

 

[rootone]

... The point is it time to relook at the entire cosmological problem as it is a fact that there are more and more anomalies concerning every aspect of the standard cosmological theory components due to multi spectrum data at all redshifts.

If you convinced about that then you will have to publish a theory which can explain the data better than existing models can.

 

[ohwilleke]

The terminology that I like to use is to say that it is beyond dispute and definitively established that dark matter phenomena exist. Galactic rotation curves, lensing, the success of the lamdaCDM model in describing the observed universe with respect to the parameters it describes, etc. all overwhelmingly support the existence of something causing dark matter phenomena other than GR as currently formulated and applied, and other than the SM forces and particles.

It is also true that we haven't solved the problem of what causes dark matter phenomena. There are several sub-types of dark matter particle based theories and a few modified gravity theories that make a good go of it, but there is no precise consensus solution that has been definitively established to solve all of the dark matter phenomena and to out perform all of the other approaches. There are at least several dozen other dark matter particle and modified gravity approaches that were considered seriously at one point or another and have been more or less definitively ruled out at this point.

We are perilously close to being overconstrained and ruling out all of the current candidates, although I am hopeful that another solution would come to the fore if that happened. I have my own subjective handicapping of the final contenders that are being tested now. The good news is that there is a lot of data that has not yet been gathered or has not been analyzed with sufficient computing power, but can be gathered or computed within the lifetimes of most of the people reading this comment, which will materially improve our ability to discriminate between the accuracy of different proposed solutions, and to narrow the parameter space of dark matter phenomena explanations. Dark matter research is not in the potential dead end situation of the poor HEP physicists who could very well be facing a desert in which no beyond the Standard Model physics turns up at any experiment within the capacity of mankind to build for many decades to come. The path to get the information we need to answer dark matter questions is clear and we have come a long way already since we started looking. We may need to invest some serious money in space based telescopes and detectors to get the answers they need, but the book is still wide open and available to read to anyone with the right instrumentation.

Also, the assertion about a lack of a solar system signal is just flat wrong. As I explained in a recent post at my blog: "If dark matter exists in the solar system, it should exist in such a homogeneous distribution at such a low density that it is undetectable through solar system gravitational dynamics. The total amount of dark matter in the solar system (if it exists) has a mass comparable to a single medium sized asteroid, but it is spread evenly throughout the spherical space centered at the Sun and including the entire solar system out to Pluto and beyond. Dark matter adds up at the galactic level but has only insignificant relevance to solar system gravitational dynamics."

The trick is to recognize that you have to use a reasonable estimate of the galactic dark matter halo distribution and not simply assume naively that DM is distributed in the same proportions it has to ordinary matter in the universe as a whole in the Milky Way galaxy. Inferred DM amounts relative to luminous matter differ systemically between different kinds of galaxies and galactic clusters.

 

[rootone]

Maybe in 1000 years we will have domestic cleaning appliances which work by using this dark stuff.

 

[ohwilleke]

1) Direct dark matter detection, negative after 50 years search.

There are lots of perfectly reasonable dark matter models (e.g. singlet sterile neutrino dark matter that don't oscillate with other neutrinos) in which it shouldn't be possible to detect dark matter directly. All direct dark matter detection experiments assume that dark matter has some cross-section of interaction with other ordinary matter through some force, with the weak force interactions of the neutrino typically used as a benchmark. No direct dark matter detection experiment has excluded dark matter particles under about 1 GeV or cross-sections of interaction consistent with a particle that interacts with ordinary matter only via gravity and Fermi contact forces (for which the cross-section of interaction from the signal would be drowned in the baseline of the cross-section of interaction of the background neutrinos).

2) Solar system area search for dark matter, negative for dark matter.

There shouldn't be enough dark matter in the solar system or a sufficiently non-homogeneous distribution of it, to be discernible from solar system gravitational dynamics. The total amount of dark matter expected for the solar system has a mass on the order of a small asteroid and would be spread fairly evenly throughout the solar system.

3) Local universe search for dark matter, negative for dark matter.

False. Lensing data and the dynamics of objects in the local universe clearly indicate that there are dark matter pheneomena in the local universe.

4) Observed spiral galaxy central form, does not agree with simulations for galaxy formation/evolution with dark matter. Cusp problem.

This is a problem with a particular dark matter paradigm called "Cold Dark Matter" which presumes thermal relic dark matter particles with masses on the order of 10s to 100s of GeVs that interact via the weak force and gravity, but not the strong or electromagnetic forces, for which supersymmetry theories provided multiple plausible candidates.

But there are a variety of ways to solve that problem. One is to use a lighter dark matter candidate (mass ca. keV) which is called "Warm Dark Matter". Another is to assume that there is a medium range force that causes dark matter to interact with other dark matter (but not with ordinary matter) via roughly MeV mass bosons with roughly the strength of the electromagnetic force.

This is also as good a place as any to explain that "Cold Dark Matter" as used in the lambdaCDM model's definition is a false friend which means something different when a CDM model is used to explain, for example, galactic rotation curves.

As used in the lambdaCDM model, a dark matter particle includes every kind of particle that would qualify as warm dark matter (WDM) or cold dark matter, but in other contexts, CDM refers exclusive to thermal relic dark matter with mass of about 5-10 GeV or more.

5) Satellite galaxy crisis

This too is a problem particular to the "Cold Dark Matter" paradigm that can be solved with either lighter "Warm Dark Matter" or with self-interacting dark matter.

The amount of galaxy group scale structure that you see in a system is essentially a function of the mean velocity of dark matter particles which in a thermal relic scenario is basically a function of dark matter particle mass. The lighter your dark matter particles, the fewer satellite galaxies you will have on average. They heavier your dark matter particles the more satellite galaxies you will have on average. This is one of the most obvious instances where tweaking one parameter, dark matter particle mass, of your model can fit it to observation without further difficulties.

The finding that a plane of satellite galaxies based on observations appears to be ubiquitous for all spiral galaxies, (>7σ confidence), published in Nature, is a big deal. i.e. Galaxy growth by mergers should produce a sphere of satellite galaxies not a narrow plane of satellite galaxies.

The assumption that galaxy growth should produce a sphere of satellite galaxies is not well established. The observation is notable, but it isn't obvious evidence one way or the other because the status quo evolution isn't terribly well understood in this respect.

More generally, there are a number of serious methodological issues with the simulations that are used to compare universes with hypothetical varieties of dark matter with observation, some of which rescue otherwise troubled DM theories, and others of which are challenging for DM theories:
1. Some of the cusp problem, for example, is due to the failure of simulation models to consider gravitational interactions with ordinary matter (often simulations are run in dark matter only universes).
2. Simulations routinely disregard GR effects and simply reply on Newtonian gravity. This is less bad that you would naively assume and it certainly isn't necessary to use full fledged GR to do an accurate numerical model at this scale, but there are some post-Newtonian tweaks that arise as a result of the differences between GR and Newtonian gravity to be discernible at this scale which should be incorporated, which is hard but not impossible as computers become more powerful. For example, GR clearly treats a rotating disk of matter differently than Newtonian gravity does, even though the differences are rather subtle.
3. Simulations usually make some pretty unrealistic assumptions about galaxy formation that make dark matter models seem to perform better than they would if realistic assumptions were used instead.

It isn't entirely clear how the various models will shake out as these issues with the computer simulations are resolved.

And, there are a few things that DM theories do quite well, such as predict the dynamics of "RAVE" stars in the Milky Way galaxy that are significantly above or below the plane of the Milky Way's spiral galaxy.

On the other hand, there are some things that DM theories generically (i.e. without regard to parameters like DM particle mass or known problems with simulation methods) do rather poorly. For example, DM theories generically under predict the proportion of spiral galaxies that lack a bulge. They generically fail to predict that the ratio of dark matter to luminous matter in elliptical galaxies is lower when they are more nearly spherical, and higher when they are less spherical. They predict much more scatter between the ratio of dark matter to luminous matter in spiral galaxies relative to their size than is actually observed if galaxy formation is just a product of random collisions of clumps of matter in the early universe according to GR alone. DM theories, generically, fail to predict the fine level wavelike texture of the distribution of stars in spiral galaxies and elliptical galaxies; instead they predict a smooth texture which is not observed.

Systems like the Bullet Cluster disfavor many (but not all) modified gravity alternatives to dark matter, but also place some serious constraints on dark matter parameters.

For example, the most prominent modified gravity theory, MOND, does a wonderful job of predicting (in advance) galactic rotation curves of every kind of galaxy from dwarf to elliptical with just a single experimentally fixed parameter. This by itself strongly hints at a fairly simple mechanism to explain this dark matter phenomena since one degree of freedom can explain far more than one might naively expect. But, this toy model phenomenological model also has a variety of known flaws: (1) it isn't relativistic although a relativistic extension of it called TeVeS exists, (2) it systemically underestimates the magnitude of dark matter pheneomena in galactic clusters, (3) it does a poor job of predicting the dynamics of RAVE stars, (4) it is inconsistent with the Bullet Cluster in its original form, and (5) it requires a slight tweak when there are two galaxies with heavily overlapping gravitational fields. But, another modified gravity theory, called MOG (for modified gravity) by Professor Moffat, lacks problems (1), (2) and (4) and hasn't been tested against RAVE star dynamics or (5) at this point.

I've seen some quite impressive early efforts to modify gravity by assuming that conventional GR using Einstein's equations incorrectly models the self-interactions of the gravitational field, which implies that the strength of modified gravity effects should be driven almost entirely by the overall mass of the system, and the extent to which a system is not spherical, which would not require any new experimentally measured parameters not already derivable from standard GR. This model also explains at least some observed dark energy effects and hence also the "cosmic coincidence" problem of why the amount of matter, inferred dark matter, and inferred dark energy are all of the same order of magnitude. But, there is a lot of work yet to be done to turn that into a workable completely articulated modified gravity theory.

The key bottom line point is that evidence that strongly indicts any particular dark matter or modified gravity model to explain dark matter phenomena doesn't necessarily mean that particle based dark matter paradigms or modified gravity model paradigms are failures in all of their many variations.

 

[betzalel]

The terminology that I like to use is to say that it is beyond dispute and definitively established that dark matter phenomena exist. Galactic rotation curves, lensing, the success of the lamdaCDM model in describing the observed universe with respect to the parameters it describes, etc. all overwhelmingly support the existence of something causing dark matter phenomena other than GR as currently formulated and applied, and other than the SM forces and particles.

It is also true that we haven't solved the problem of what causes dark matter phenomena. There are several sub-types of dark matter particle based theories and a few modified gravity theories that make a good go of it, but there is no precise consensus solution that has been definitively established to solve all of the dark matter phenomena and to out perform all of the other approaches. There are at least several dozen other dark matter particle and modified gravity approaches that were considered seriously at one point or another and have been more or less definitively ruled out at this point.
.

betzalel,

Dark matter or changes to general relativity do not explain the correlated structure of spiral galaxy parameters which is a paradox. The dark matter papers ignore the correlated structure paradox.

Clouds of dark matter particles will not cause Goldlock's increases of spiral galaxy rotational (not too much or not too little) in direct proportion to the spiral galaxy's mass.

There is a continual unexplained evolution in spiral galaxy properties. Why? What is causing the increase in rotational speed as the spiral galaxy grows in size.

Heirarchical galaxy formation (betzalel, with dark matter or with modified gravity) simply does not fit the constraints set by the correlation structure in the Equatorial Survey.

The solution must explain what is observed. Note there are other anomalies concerning how spiral galaxy grow.

1) As noted, there must be some mechanism that stops/inhibits the merger of spiral galaxies. Mergers (random mergers of two spiral galaxies with stars) will gradually change spiral galaxies into elliptical galaxies or elliptical like galaxies and will produce random sized galaxy bulges. That is not observed. Mergers will most definitely not cause the angular momentum of a galaxy to increase in direct proportion to the spiral galaxy's mass. What is observed is that spiral galaxies show a continual tightly controlled spectrum of growth with a bulge that grows in direct proportion to the mass of the super large object in the center of almost all galaxies.

What that indicates is the grow of the spiral galaxy is somehow connected with the grow of the super massive object at the center of almost all galaxies.

2) If spiral galaxies do not grow by mergers, how then do they grow?

3) How do spiral galaxies gain angular momentum in direct proportion to their mass?http://www.nature.com/nature/journal/v455/n7216/abs/nature07366.html

http://arxiv.org/ftp/arxiv/papers/0811/0811.1554.pdf

Galaxies appear simpler than expected

Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment, and feedback from supernova explosions and supermassive black holes1. The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter2,3,4. The properties of an individual galaxy should be controlled by six independent parameters including mass, angular-momentum, baryon-fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free of optical selection effects5, shows five independent correlations among six independent observables, despite having a ...

... This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our dataset. Such a degree of organization appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter paradigm in cosmology6.

...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey..

 

[rootone]

... there must be some mechanism that stops/inhibits the merger of spiral galaxies.

What makes you think this?
It''s generally accepted our that our galaxy will merge with Andromeda galaxy in the very long run.

 

[ohwilleke]

Dark matter or changes to general relativity do not explain the correlated structure of spiral galaxy parameters which is a paradox. The dark matter papers ignore the correlated structure paradox. Clouds of dark matter particles will not cause Goldlock's increases of spiral galaxy rotational (not too much or not too little) in direct proportion to the spiral galaxy's mass.

This is simply inaccurate. The correlated one dimensional structure of spiral galaxy parameters, first described with as the Tully-Fischer relation, historically, was the primary motivation for the original modified gravity theory, MOND, and essentially all subsequent modified gravity theories address this issue.

Dark matter models address this problem as well, although with not quite such a tight fit to the galactic mass as modified gravity models. Mostly this arises because dark matter halos are less capable of maintaining distinct form than ordinary matter due to their lack of non-gravitational interactions. In dark matter models, the distribution of ordinary matter in galaxies is homogenized by the powerful role that dark matter halos (which tend to be fairly homogeneous at any given size) exert on the formation of galaxies and the distribution of ordinary matter within them. There is also gravitational feed back in the other direction from the baryonic matter to the dark matter halo, in which the disk-like distribution of baryonic matter's tugs the shape of the dark matter halo away from a sphere towards a rugby ball shape.

Let me put this another way. Dark matter models became popular because in crude simulations they crudely reproduced what we observed, with some very simple starting assumptions. They do work. Particular versions of them may not perfectly fit the data, but the extent to which a very simple version of them can come reasonably close to reality with relatively arbitrarily chosen parameters shows why these models are promising, even if there is more fine tuning of the model that is necessary to fit the better resolved data matched to better simulations, than one would have initially hoped.

It is one thing to say that this particular model or that particular model has a flaw, and it is another to indict the entire paradigm with objections that really only apply to particular models and are not generic.

As noted by another poster earlier, this is a constructive model building process. The only way somebody gets a turn to come to the podium and say something that people will listen to is to propose an alternative to the status quo that is better. Saying that there is a problem with a model is just another way of saying that the model needs to be modified to produce a better result. Until the problem is solved once and for all, one has to keep trying to formulate better and better models until we get it right.

Currently, we are fortunate to have work done on two separate paradigms which both seem promising: particle based dark matter paradigms, and modified gravity paradigms. If you can come up with a third paradigm that is better than either of the other two or some combination of them, more power to you. Tell us all.

 

[betzalel]

What makes you think this?
It''s generally accepted our that our galaxy will merge with Andromeda galaxy in the very long run.

betzalel,
As noted the correct solution must explain the correlated spiral galaxy properties as noted in the Disney paper which is a paradox. None of the dark matter papers or galaxy simulation papers discuss the Disney finding as it is paradox. The correct solution cannot be dark matter or changing gravity. (See my comment below.)

The correct solution must in addition to explaining the correlated spiral galaxy properties must explain how spiral galaxies grow (their means of grow cannot be mergers, as a merger will not produce a giant bulgeless galaxy) and why they do not show evidence of mergers.

Something is stopping/inhibiting spiral galaxies from merging and somehow they still grow.

Note as the spiral galaxies grow and age they gradually develop a bulge whose size is directly proportional to the mass of the super massive object in their core.

There is a third mystery. If spiral galaxy growth is not by mergers how does the super massive object in their center grow?

http://arxiv.org/abs/1009.3015

BULGELESS GIANT GALAXIES CHALLENGE OUR PICTURE OF GALAXY FORMATION

BY HIERARCHICAL CLUSTERING

We inventory the galaxies in a sphere of radius 8 Mpc centered on our Galaxy to see whether giant, pure-disk galaxies are common or rare. We find that at least 11 of 19 galaxies with Vcirc > 150 km s-1, including M101, NGC 6946, IC 342, and our Galaxy, show no evidence for a classical bulge.

We conclude that pure-disk galaxies are far from rare. It is hard to understand how bulgeless galaxies could form as the quiescent tail of a distribution of merger histories.

Recognition of pseudo bulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many giant, pure-disk galaxies with no evidence for merger-built bulges?

http://arxiv.org/abs/1001.4542v1

THE EDGE-ON PERSPECTIVE OF BULGELESS, SIMPLE DISK GALAXIES

However, other studies claim that neither different kinds of feedback (D’Onghia & Burkert 2004; D’Onghia et al. 2006) nor increased numerical resolution (K¨ockert & Steinmetz 2007; Piontek & Steinmetz 2009a) can resolve the angular momentum problem completely. Therefore, the formation of simple disk galaxies in a cosmological framework is not yet well understood (Burkert 2008; Mayer et al. 2008), and a detailed understanding of this topic is just at the beginning

.

 

[ohwilleke]

The argument that there is bulgeless galaxies is essentially an argument for favoring modified gravity theories over dark matter theories. The expectation of near universal bulges is particular to galaxy formation scenarios observed in particle dark matter models. It is not an argument that there is no explanation for this pattern under any theory.

 

[betzalel]

This is simply inaccurate. The correlated one dimensional structure of spiral galaxy parameters, first described with as the Tully-Fischer relation, historically, was the primary motivation for the original modified gravity theory, MOND, and essentially all subsequent modified gravity theories address this issue.

Dark matter models address this problem as well, although with not quite such a tight fit to the galactic mass as modified gravity models. Mostly this arises because dark matter halos are less capable of maintaining distinct form than ordinary matter due to their lack of non-gravitational interactions. In dark matter models, the distribution of ordinary matter in galaxies is homogenized by the powerful role that dark matter halos (which tend to be fairly homogeneous at any given size) exert on the formation of galaxies and the distribution of ordinary matter within them. There is also gravitational feed back in the other direction from the baryonic matter to the dark matter halo, in which the disk-like distribution of baryonic matter's tugs the shape of the dark matter halo away from a sphere towards a rugby ball shape.

Let me put this another way. Dark matter models became popular because in crude simulations they crudely reproduced what we observed, with some very simple starting assumptions. They do work. Particular versions of them may not perfectly fit the data, but the extent to which a very simple version of them can come reasonably close to reality with relatively arbitrarily chosen parameters shows why these models are promising, even if there is more fine tuning of the model that is necessary to fit the better resolved data matched to better simulations, than one would have initially hoped.

betzalel,

Problem 1: Analysis supports the assertion that there is a precise angular momentum gain (not random angular momentum gain) as the spiral galaxy gains mass. How is that possible with mergers? It appears dark matter and/or modified gravity does not enable spiral galaxies to precisely gain angular momentum as they gain mass via mergers. The paradox is the standard model for galaxy growth assumes galaxies grow by mergers. Mergers however produce random changes in angular momentum not precise changes in angular momentum. A precise gain in angular momentum is required to produce the tight correlated set of spiral galaxy parameters which Disney discovered.

Could you provide a paper link and a Coles Note explanation as to how spiral galaxies gain angular momentum as they gain mass via mergers using dark matter or modified gravity? What you have said in this forum does not agree with Disney's comment.

http://arxiv.org/ftp/arxiv/papers/0811/0811.1554.pdf

...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey..

Problem 2: Evidence that a set of galaxies (bulgeless disc galaxies) grow without mergers. Two related issues. 1) Why are there no mergers? 2) If these galaxies did not have mergers how then did they grow?

How is the mass getting into the galaxy in a manner such that a bulge is not produced?

Note the bulgeless galaxies form a continual set that has larger and larger tiny bulges. This supports the assertion that the set of bulgeless galaxies gradually develop a bulge and become standard spiral galaxies. The size/mass of the spiral galaxies bulge is unexplainably directly proportional to the mass of the super massive object which is in the center of almost every galaxy. The super massive object somehow also gains mass in some mysterious way as the bulgeless galaxies gain mass without mergers.

http://arxiv.org/abs/1009.3015

BULGELESS GIANT GALAXIES CHALLENGE OUR PICTURE OF GALAXY FORMATION BY HIERARCHICAL CLUSTERING

We inventory the galaxies in a sphere of radius 8 Mpc centered on our Galaxy to see whether giant, pure-disk galaxies are common or rare. We find that at least 11 of 19 galaxies with Vcirc > 150 km s-1, including M101, NGC 6946, IC 342, and our Galaxy, show no evidence for a classical bulge.

We conclude that pure-disk galaxies are far from rare. It is hard to understand how bulgeless galaxies could form as the quiescent tail of a distribution of merger histories.

Recognition of pseudo bulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many giant, pure-disk galaxies with no evidence for merger-built bulges?

Problem 3: There are no type B dwarf satellite galaxies (dwarf satellite galaxies that are spherically orientated about the spiral galaxy as opposed to type A which are located in a plane about the spiral galaxy) which is further support that there are no mergers and in addition this author assertions shows as there are no type B dwarfs that dark matter does not exist. Note modified gravity does explain the above.

http://arxiv.org/abs/1204.2546v2

The dark matter crisis: falsification of the current standard model of cosmology

The current standard model of cosmology (SMoC) requires The Dual Dwarf Galaxy Theorem to be true according to which two types of dwarf galaxies must exist: primordial dark-matter (DM) dominated (type A) dwarf galaxies, and tidal-dwarf and ram-pressure-dwarf (type B) galaxies void of DM. Type A dwarfs surround the host approximately spherically, while type B dwarfs are typically correlated in phase-space. Type B dwarfs must exist in any cosmological theory in which galaxies interact. Only one type of dwarf galaxy is observed to exist on the baryonic Tully-Fisher plot and in the radius-mass plane. TheMilkyWay satellite system forms a vast phase-space-correlated structure that includes globular clusters and stellar and gaseous streams. Other galaxies also have phase-space correlated satellite systems. Therefore, The Dual Dwarf Galaxy Theorem is falsified by observation and dynamically relevant cold or warm DM cannot exist.

Communication is serial and is not instantaneous. There needs to be time for thought about the problem and time to understand what the problem is. This problem is holistic. It is obvious or it should be obvious that the observations will point to the correct solution. The trick to solving the problem is to first at the look at the observations, think about the observations, understand the implications of the observations and then propose a solution. There are piles and piles of related paradoxes.

Issue for a couple of other threads.

There is another set of paradoxes concerning the downsizing of the super massive object mass that is in the center of almost ever galaxy with redshift (the mass of the objects in the center of galaxies get smaller with redshift rather than larger with redshift, the super massive objects shrink with time as it is assumed greater redshift objects are older objects, where did the old large super massive objects go?) and quasar evolution with redshift.

 

[betzalel]

The observational fact that there is a correlated structure of spiral galaxy parameters has astonishing implications.

It is not possible to fine 'tune' a dark matter or a modified gravity model to create a continuum of spiral galaxy angular momentum that is directly proportional to spiral galaxy mass if spiral galaxies grow by mergers, due to conservational of angular momentum applied to the random merger process.

The following explains why that assertion is correct based on fundamental physics.

Disney asserts in his paper:

Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey

The specialists have ignored the implications of Disney's finding, that there is a precise continuum of increasing angular momentum of spiral galaxies, with increasing galaxy mass. That observation fact rules out both 'Heirarchical' mechanisms as the principal method by which galaxies gain mass and grow and also requires a non gravitation mechanism to produce the precise angular momentum increase correlating with galaxy mass. A dark matter or modified gravitational model will produce a log-normal distribution of angular momentums.

Does everyone understand conservation of angular momentum? Does everyone understand Disney's comment " Simulations produce spins, independent of mass, with a log-normal distribution"?

I have always been curious what produces galactic angular momentum. The standard theory is that differential speeds of gas clouds when the galaxies first condense sets the angular momentum. Subsequence mergers may add or reduce that angular momentum depending on the random spatial arrangement of the merger. This type of mechanism will produce a log-normal distribution of angular momentum rather than a precise continuum of angular momentum that increases with galaxy mass.Fundamentals of Physics Extended Fifth Edition H.R.W.

Page 289

12-8 Conservation of Angular Momentum

If the net external torque acting on a system is zero, the angular momentum L of the system remains the same, no matter what changes take place within the system.

If any component of the net external torque on a system is zero, then that component of the angular momentum of the system along that axis cannot change, no matter what changes take place within the system.

http://arxiv.org/ftp/arxiv/papers/0811/0811.1554.pdf

...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey..

 

[rootone]

there must be some mechanism that stops/inhibits the merger of spiral galaxies.

My understanding is that galaxies can and do merge and that spirals are no exception.
Also that we have accumulated a significant amount of astro photography which actually shows galaxies in different stages of merger.
In the case of spirals of roughly equal size merging, the result apparently is what might be expected, - that both systems become heavily structurally disrupted and their contents eventually settle into an elliptical galaxy carrying the sum of angular momentum of the original galaxies.
(Well not quite all of it, since it's expected that some star systems will end up being ejected altogether.)
That's the ordinary matter of course, but I suppose that dark matter content behaves similarly since the interaction is gravitational.

In the case of the future collision of the Milky way and Andromeda, a merger of this sort seems to be inevitable, though no one can predict the form of exact final result
If this merger cannot happen then what is going to intervene which will prevent it?, and why do we have the astro photography showing merges in progress?
Are you saying that these images are being misinterpreted as merging galaxies when really something different is happening?

 

[betzalel]

My understanding is that galaxies can and do merge and that spirals are no exception.
Also that we have accumulated a significant amount of astro photography which actually shows galaxies in different stages of merger.
In the case of spirals of roughly equal size merging, the result apparently is what might be expected, - that both systems become heavily structurally disrupted and their contents eventually settle into an elliptical galaxy carrying the sum of angular momentum of the original galaxies.
(Well not quite all of it, since it's expected that some star systems will end up being ejected altogether.)
That's the ordinary matter of course, but I suppose that dark matter content behaves similarly since the interaction is gravitational.

In the case of the future collision of the Milky way and Andromeda, a merger of this sort seems to be inevitable, though no one can predict the form of exact final result
If this merger cannot happen then what is going to intervene which will prevent it?, and why do we have the astro photography showing merges in progress?
Are you saying that these images are being misinterpreted as merging galaxies when really something different is happening?

Yes, it appears that what was been interpreted to be a merger may not be a merger.

70% of the galaxies in our local universe are spiral including bulgeless spiral galaxies which supports the assertion that spiral galaxies avoid mergers as major mergers of two spiral galaxies will produce an elliptical galaxy and mergers will most definitely create bulges. Observationally it appears bulgeless spiral galaxies turn into normal spiral galaxies.

As noted, mergers produce random increases in angular momentum. If there are mergers then it seems there would no longer be a tight correlation of spiral galaxy parameters.

What is required is a mechanism that enables a spiral galaxy to gain mass and to gain a specific amount of angular momentum and a second mechanism (perhaps connected to the first) that enables spiral galaxies to avoid mergers.

The specialists are discussing the same issues.

http://arxiv.org/pdf/astro-ph/0702585v1.pdf

THE MILKY WAY: AN EXCEPTIONALLY QUIET GALAXY; IMPLICATIONS FOR THE FORMATION OF SPIRAL GALAXIES

Disk galaxies constitute the majority of the galaxy population observed in the local universe. They represent 70% of intermediate mass galaxies (stellar masses ranging from 3× 10^10 to 3 × 10^11 M⊙), which themselves include at least two-third of the present-day stellar mass (e.g., Hammer et al. 2005).However, there are several outstanding difficulties with this standard scenario. One such difficulty is the so-called angular momentum problem. That is, simulated galaxies cannot reproduce the large angular momentum observed in nearby spiral galaxies (e.g., Steinmetz & Navarro 1999). Another is the assumed absence of collisions during and after the gas condensation process. Indeed, the hierarchical nature of CDM cosmology predicts that galaxies have assembled a significant fraction of their masses through collisions with other galaxies. It is likely that such collisions would easily destroy galactic disks (e.g., Toth & Ostriker 1992). Although the accretion of satellites may preserve the disk, it is also true that major collisions would certainly affect it dramatically.

The key questions are then: Do major collisions always destroy disks? Can major collisions lead to the formation of new disks? Do these rebuilt or altered disks have properties consistent with those of local galaxies?

Combining the pair fraction and characteristic time scale estimates suggests that for a present-day galaxy with a stellar mass larger than 3 × 1010 M⊙, the chance it has experienced a major merger since z=1 is 50±17%, 75±25% and 70% according to Lotz et al. (2006), Hammer et al. (2005), and Bell et al. (2006), respectively1. Although less certain, integrating the merger rate to higher redshift implies that a typical bright galaxy may have experienced up to four to five major merging events since z=3 (Conselice et al. 2003).

The high frequency of major mergers may be a real problem for the standard theory of disk formation. Assuming that protogalactic disks lie in the distant universe, how can this be reconciled with an absence of major collisions? How can we explain the large fraction of local disks if major mergers (with mass ratio ranging from 1:1 to 1:3) unavoidably lead to the formation of an elliptical? Even at z less than 1 the observations are challenging for the standard scenario

.

http://arxiv.org/ftp/arxiv/papers/0811/0811.1554.pdf

...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey..

 

[ohwilleke]

Kroupa explains why modified gravity can produce the observed spectrum while WDM and CDM cannot. http://arxiv.org/pdf/1204.2546.pdf See especially, pages 28-36 and also here http://arxiv.org/pdf/1006.1647.pdf

Another proposal is cold neutrino dark matter. http://iopscience.iop.org/0295-5075/86/5/59001/fulltext/epl_86_5_59001.html de Vega argues that WDM can manage to reproduce what we see http://arxiv.org/pdf/1004.1908.pdf Kesselman offers a self-interacting DM scenario that purports to rise to the challenge. http://arxiv.org/pdf/0912.4177.pdf

 

[betzalel]

Kroupa explains why modified gravity can produce the observed spectrum while WDM and CDM cannot. http://arxiv.org/pdf/1204.2546.pdf See especially, pages 28-36 and also here http://arxiv.org/pdf/1006.1647.pdf

Another proposal is cold neutrino dark matter. http://iopscience.iop.org/0295-5075/86/5/59001/fulltext/epl_86_5_59001.html de Vega argues that WDM can manage to reproduce what we see http://arxiv.org/pdf/1004.1908.pdf Kesselman offers a self-interacting DM scenario that purports to rise to the challenge. http://arxiv.org/pdf/0912.4177.pdf

betzalel,

Kroupa's papers push MOND. Kroupa discusses satellite galaxies in his paper. Based on that analysis he asserts that CDM cannot explain the observations in the local group.

Kroupa does not discuss the Goldilocks Spiral Galaxy Angular Momentum paradox that spiral galaxies have a very, tight correlated set of parameters that is not possible with hierarchical galaxy formation.

Kroupa's papers do not reference Disney's paper.

Kroupa's paper do not discuss the conservation of angular momentum, spiral galaxy existence paradox. Kroupa proposes changing gravity without logical reason. He does not propose changing the laws angular momentum for no logical reason to try to solve the Spiral existence paradox of the Spiral Galaxy Goldilock Angular momentum paradox.

There are multiple very basic fundamental paradoxes concerning galaxy morphology at redshift and concerning correlate spiral galaxy parameters and concerning the existence of a graduated set of flat, bulgeless spiral galaxies.

Paradox 1 - Spiral Galaxy Existence Paradox, Conservation of Momentum/Merger Paradox,

Why are there any spiral galaxies? 2/3 of the mass in the local universe is in spiral galaxies. Due to the conservation of angular momentum (angular momentum cannot be created or destroyed) the merger of two spiral galaxies which have different angular momentum (the problem is the angular momentum of the stars of the two merging galaxies) will produce an elliptical galaxy or an elliptical like galaxy not a spiral galaxy. This is a very, very basic paradox. There must be some unknown mechanism that is stopping spiral galaxies from merging. Dark matter is not a solution to this problem. Changing the laws of gravity does explain this observation. The problem is the conservation of angular momentum and the mergers of spiral galaxies that have stars.

How do spiral galaxies avoid mergers? What is stopping spiral galaxies from merging?

The existence of a set of a graduated set of flat bulgeless spiral galaxies makes this paradox more sever. The bulgeless galaxies somehow grow and turn into normal spiral galaxies.Paradox 2: Goldilocks Spiral Galaxy Momentum Paradox, Tightly Correlated, Graduated increasing Angular Momentum and four other Spiral Galaxy Parameters

Disney discovered that spiral galaxies have a tightly correlated set of parameters. Mergers will in addition to producing elliptical like galaxies, will not produce spiral galaxies that have a graduating increase in angular momentum.

As I noted this paradox requires a Goldilocks angular momentum mechanism which will add the correct amount of angular momentum (not too much, not too little) as the galaxy grows in mass to maintain the tight correlation of galaxy parameters.Galaxy spin is thought (assumed) to be the result of early tidal torquing. That assumption is not correct. There needs to be new mechanism (I repeat, a new mechanism) that produces a precise graduated increase in momentum as the spiral galaxy grows/gains mass.

Simulations produce spins (spiral galaxy angular momentum), independent of mass, with a log-normal distribution.http://arxiv.org/ftp/arxiv/papers/0811/0811.1554.pdf

Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment, and feedback from supernova explosions and supermassive black holes1. The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter2,3,4. The properties of an individual galaxy should be controlled by six independent parameters including mass, angular-momentum, baryon-fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free of optical selection effects5, shows five independent correlations among six independent observables, despite having a ...

... This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our dataset. Such a degree of organization appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter paradigm in cosmology6.

...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey..

http://arxiv.org/pdf/astro-ph/0702585v1.pdf

THE MILKY WAY: AN EXCEPTIONALLY QUIET GALAXY; IMPLICATIONS FOR THE FORMATION OF SPIRAL GALAXIES

Disk galaxies constitute the majority of the galaxy population observed in the local universe. They represent 70% of intermediate mass galaxies (stellar masses ranging from 3× 10^10 to 3 × 10^11 M⊙), which themselves include at least two-third of the present-day stellar mass (e.g., Hammer et al. 2005).

However, there are several outstanding difficulties with this standard scenario. One such difficulty is the so-called angular momentum problem. That is, simulated galaxies cannot reproduce the large angular momentum observed in nearby spiral galaxies (e.g., Steinmetz & Navarro 1999). Another is the assumed absence of collisions during and after the gas condensation process. Indeed, the hierarchical nature of CDM cosmology predicts that galaxies have assembled a significant fraction of their masses through collisions with other galaxies. It is likely that such collisions would easily destroy galactic disks (e.g., Toth & Ostriker 1992). Although the accretion of satellites may preserve the disk, it is also true that major collisions would certainly affect it dramatically.

The key questions are then: Do major collisions always destroy disks? Can major collisions lead to the formation of new disks? Do these rebuilt or altered disks have properties consistent with those of local galaxies?Combining the pair fraction and characteristic time scale estimates suggests that for a present-day galaxy with a stellar mass larger than 3 × 1010 M⊙, the chance it has experienced a major merger since z=1 is 50±17%, 75±25% and 70% according to Lotz et al. (2006), Hammer et al. (2005), and Bell et al. (2006), respectively1. Although less certain, integrating the merger rate to higher redshift implies that a typical bright galaxy may have experienced up to four to five major merging events since z=3 (Conselice et al. 2003).

The high frequency of major mergers may be a real problem for the standard theory of disk formation. Assuming that protogalactic disks lie in the distant universe, how can this be reconciled with an absence of major collisions? How can we explain the large fraction of local disks if major mergers (with mass ratio ranging from 1:1 to 1:3) unavoidably lead to the formation of an elliptical? Even at z less than 1 the observations are challenging for the standard scenario

Fundamentals of Physics Extended Fifth Edition H.R.W.

Page 289

12-8 Conservation of Angular Momentum

If the net external torque acting on a system is zero, the angular momentum L of the system remains the same, no matter what changes take place within the system.

If any component of the net external torque on a system is zero, then that component of the angular momentum of the system along that axis cannot change, no matter what changes take place within the system.

 

[ohwilleke]

Actually, all of the papers that I referenced cite Disney and engage that issue. Hierarchical formation is an idea specific to DM particle models which he attacks with arguments almost the same as the ones that you are advancing. I used list of papers citing Disney to find them. Please read more carefully. You are reading without thinking.

Also Kroupa proposes changing gravity because it fits the data better. This is a very logical reason.

 

[betzalel]

Actually, all of the papers that I referenced cite Disney and engage that issue. Hierarchical formation is an idea specific to DM particle models which he attacks with arguments almost the same as the ones that you are advancing. I used list of papers citing Disney to find them. Please read more carefully. You are reading without thinking.

Also Kroupa proposes changing gravity because it fits the data better. This is a very logical reason.

Kroupa notes the Disney finding that spiral galaxies are controlled by a single parameter which invalidates the assumption that spiral galaxies grow by hierarchical mergers which is a paradox. How then do they grow?

Kroupa does not assert that MOND explains that paradox. It does not.

If there are piles and piles of observations that do not support a theory, the theory is incorrect. In private industry when there are piles and piles of paradoxes, a group is assigned the task to relook at every assumption and to think out of the box. i.e. To ensure that every possible alternative (I repeat every possible alternative) is systematically examined. Curiously that approach leads to breakthroughs. There are easily three or four major breakthroughs lying around in this field with astonishing implications.http://arxiv.org/ftp/arxiv/papers/0811/0811.1554.pdf

...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey...

Consider spin alone and try to explain the very existence of bulgeless galaxies which observationally magically gain spin (do you remember how I try to explain that momentum is conserved hence when two large spiral galaxies merge what is created is an elliptical like galaxy not a bulgeless galaxy or spiral galaxy). What is required is a mechanism that stops/inhibits the merging of spiral galaxies, including bulgeless galaxies and a mechanism that causes spiral galaxies to spin faster as they gain mass by the new mechanism which is very, very, different than the old assuming mechanism by which galaxies grew.

16% to 32% of the spiral galaxies are made up of bulgeless galaxies and 2/3 of galaxy masses in the local universe is made up of spiral galaxies. The percentage of bulgeless galaxies does not change from z=0 to Z=1.

Note to explain Disney's finding spiral galaxies need to gain momentum as they get larger and there needs to be an explain as to why there is no morphological change in spiral galaxies from z=0 to z=1. The problem is not how to solve those problems, the problem, the explanation as to why this problem is not solved is the implications of the problems' solution is unbelievable and hence is unimaginable.

...In the current cold DM ( CDM) framework of structure formation and evolution, galaxies in DM halos grow hierarchically by the absorption of smaller substructures in sub halos (Searle & Zinn 1978; White & Rees 1978; Blumenthal et al. 1984). This means that disk galaxies have always been subject to merging and interaction. Almost all galaxies with present halo mass comparable to the Milky Way (MDM 10^13solar masses to 10^11 solar masses) morphological transformations of disk galaxies. At the upper limit, a merger may cause the total destruction of the disk and the formation of a spheroidal, elliptical galaxy (e.g., Toomre 1977; Barnes 1992; Gardner 2001; Cox & Loeb 2008). Massive disks can then be rebuilt from gas deposited in a gas-rich (major) merger (Hammer et al. 2009; Robertson & Bullock 2009; Yang et al. 2009) supported by the additional accretion of cold gas (Dekel & Birnboim 2006). However, these so-called rebuilt scenarios assume that disks will be reformed around preexisting spheroidal bulges (Steinmetz 2003; Springel& Hernquist 2005). In less violent cases of major mergers, spheroidal bulges can formed by dynamically heated disk stars and accreted material (Aceves et al. 2006; Bournaud et al. 2007; Khochfar 2009). In addition, new bulge stars can be formed from disk gas that lost its angular momentum by nonaxisymmetric distortions due to galaxy-galaxy interactions (Noguchi 2001; Benson et al. 2004; Hopkins et al. 2009a; Koda et al. 2009)
.

According to these model predictions, not many simple disks should have survived the cosmological evolution.

The fraction of the simple disk class Sd(f) is 16% among the disk galaxies in the Kautsch et al. (2006a) catalog. This fraction increases to 32% if the seemingly bulgeless (but less strictly defined) Scd(f) types are included.

Bulgeless galaxies are located in all environments, ranging from low to high density (Kautsch et al. 2005, 2009). The majority of these galaxies are weakly associated with galaxy clusters and can be found in more isolated environments comparable to galaxy groups and the field (Kudrya et al. 1997; Karachentsev 1999b; Kautsch et al. 2009). Because of the low relative velocities of group galaxies, merging and morphological processes that transform late-type galaxies into bulgedominated and spheroidal galaxies are common in the group environment (e.g., Barnes 1985; Kautsch et al. 2008; Tran et al. 2008). This implies that simple disks either have to be stable against morphological preprocessing or are located in this environment due to recent infall.

Field studies show that the number density of large bulgeless galaxies is constant (maybe slightly increasing) at redshifts z 0 to 1 whereas the number of galaxies with bulges decreases at larger distances (Sargent et al. 2007; Dom´ınguez-Palmero & Balcells 2009).

Simple disks are not a separate morphological class, but rather at the end of a smooth continuum without a well-defined boundary (Matthews & Gallagher 1997; Kautsch et al. 2006a).

On average, bulgeless disks rotate slower than galaxies with bulges as shown in Figure 3. .

 

[ohwilleke]

In private industry when there are piles and piles of paradoxes, a group is assigned the task to relook at every assumption and to think out of the box. i.e. To ensure that every possible alternative (I repeat every possible alternative) is systematically examined.

Mostly off topic, but I can't recall ever seeing private industry do what you describe in that manner, although I wish they did. Private industry usually tends to look more like Dilbert than like a paragon of innovative competence. The more common phenomena is an evolutionary version of "creative destruction." Lots of people try lots of different things in a completely unsystematic and often irrational manner, some of those approaches outperform the status quo, and when they do, they destroy an entire existing industry and replace it with a new one based on a new idea that managed to work better than the status quo more out of dumb luck than out of careful deliberation.

 

[ohwilleke]

One mechanism that gets you quite a bit of the way there is as follows.

Assume that the gravitational field in a modified gravity theory has different strength in different directions around a spiral galaxy.

For example, it may be stronger in the plane of its disk (which also promotes satellite galaxy alignment in that disk) and promotes mergers by accretion from end to end spiral galaxies producing something like:

https://encrypted-tbn0.gstatic.com/...C7iFX8JiUwUdKMI-OMmIZB4pfcTGAyYMLWZfj0eWJ9ddm

Meanwhile gravity might be weaker in a corresponding amount on its axis. Thus, a lot of spiral galaxies on a near collision course with each other on the wrong angle of attack would just miss each other, despite the fact that if each had a spherically symmetric gravitational field around its central black hole, they would have collided to form an elliptical or bulged spiral galaxy.

Just saying that what is a clear paradox in particle based CDM models (which are discussed in the quotations above) is not necessary such a paradox in modified gravity models and that for the most part nobody has run the simulations of modified gravity models to quantify those differences.

 

[betzalel]

One mechanism that gets you quite a bit of the way there is as follows.

Assume that the gravitational field in a modified gravity theory has different strength in different directions around a spiral galaxy.

For example, it may be stronger in the plane of its disk (which also promotes satellite galaxy alignment in that disk) and promotes mergers by accretion from end to end spiral galaxies producing something like:

https://encrypted-tbn0.gstatic.com/...C7iFX8JiUwUdKMI-OMmIZB4pfcTGAyYMLWZfj0eWJ9ddm

Meanwhile gravity might be weaker in a corresponding amount on its axis. Thus, a lot of spiral galaxies on a near collision course with each other on the wrong angle of attack would just miss each other, despite the fact that if each had a spherically symmetric gravitational field around its central black hole, they would have collided to form an elliptical or bulged spiral galaxy.

Just saying that what is a clear paradox in particle based CDM models (which are discussed in the quotations above) is not necessary such a paradox in modified gravity models and that for the most part nobody has run the simulations of modified gravity models to quantify those differences.

Paradoxes and anomalies indicate the base theory and base assumptions are incorrect. There has been sufficient information to solve the cosmological puzzle for at least a decade. It is impossible to solve a problem if the base theory and assumptions are incorrect. The solution cannot be found by guessing, by throwing theories up in the air.

There are paradoxes and anomalies associated with every pillar of the current cosmological theory. The solution to this problem is found by looking at and explaining the observational paradoxes and anomalies. The solution is not dark matter or MOND. Dark matter and/or MOND does not produce a torque which is necessary for spiral galaxies to increase spin as they grow, does not explain how spiral galaxies grow, does not explain how spiral galaxies avoid mergers, why spiral galaxies exist.

As I noted angular momentum is conserved. The merger of two spiral galaxies is at random directions and should hence produce an elliptical like galaxy not a spiral galaxy and certainly not a bulgeless galaxy.

There is no explanation as to why 2/3 of galaxy mass in the local universe is found in spiral galaxies and 16% to 32% of the spiral galaxies are bulgeless from z=0 to z=1. There is no change in galaxy morphology from z=0 to z=1 (ratio of spiral to elliptical galaxies). If spiral galaxies do not gain mass by mergers how then do they gain mass? How do spiral galaxies avoid mergers? How do spiral galaxies gain angular momentum which is required to explain Disney's observation that spiral galaxy have correlated properties?

There are weird objects in the high z universe that magically disappear and are not found in the local universe. The evolution of the universe with redshift does not make sense, is a paradox. What are the theoretical and practical differences between a fixed time cosmological theory vs an eternal cosmological theory in terms of mechanisms to explain the observations? What was happening to the universe 100 billion years ago, 150 billion years ago?

http://arxiv.org/pdf/astro-ph/0702585v1.pdf

.

The high frequency of major mergers may be a real problem for the standard theory of disk formation. Assuming that protogalactic disks lie in the distant universe, how can this be reconciled with an absence of major collisions? How can we explain the large fraction of local disks if major mergers (with mass ratio ranging from 1:1 to 1:3) unavoidably lead to the formation of an elliptical? Even at z less than 1 the observations are challenging for the standard scenario..

Fundamentals of Physics Extended Fifth Edition H.R.W.Page 289

12-8 Conservation of Angular MomentumIf the net external torque acting on a system is zero, the angular momentum L of the system remains the same, no matter what changes take place within the system.If any component of the net external torque on a system is zero, then that component of the angular momentum of the system along that axis cannot change, no matter what changes take place within the system..

 

[Gaz]

I like this a lot. (The dancing dwarf's) It doesn't come as any surprise at all though pretty much everything revolves around the next biggest thing isn't that how gravity works. And when your revolving around it you can put money on it's going to be close to the direction it's spinning the majority of the time =)

 

[ohwilleke]

Angular momentum is not conserved in galaxies anyway. If it has more angular momentum than it can gravitationally constrain then it flings some of the stars on the rim off into deep space. As new objects passing through space enter a galaxy, they may be assimilated and transfer their momentum angular and otherwise to the galaxy. A galaxy is not a closed system.

We clearly do not have enough data, because we have competing theories, whose differences are not conclusively resolved by that data.

The solution is not dark matter or MOND. Dark matter and/or MOND does not produce a torque which is necessary for spiral galaxies to increase spin as they grow, does not explain how spiral galaxies grow, does not explain how spiral galaxies avoid mergers, why spiral galaxies exist.

As I noted angular momentum is conserved. The merger of two spiral galaxies is at random directions and should hence produce an elliptical like galaxy not a spiral galaxy and certainly not a bulgeless galaxy.

MOND is just one modified gravity theory. There are many other theories in this class, some of which are yet to be discovered.

Gravity of some kind. from DM, in a modified gravity theory, or otherwise, constrains particles that would otherwise fly away from a spiral galaxy to stay within it at a constant angular rotation speed. This is well explained by both classes of theories. These theories create torque by taking stars with linear kinetic energy that pass into the plane of a spiral galaxy and using gravity to force that passing object into a circular movement around the galactic core which is the center of gravity. It is no different than the spin created if a speed skater grabs a rope connected to a pole on the ice rink and starts twisting around the pole rather than going straight. The way that gravity can create torque is elementary. What is remarkable is that the strength of the gravitational pull, in either DM theories or modified gravity theories (NOT JUST MOND!) is more than we would naively expect from the luminous matter alone.

In any situation where a galaxy is adding mass, or could shed mass, it is not a closed system and the conservation of total angular momentum does not apply.

As I explained, in some modified gravity theories, the direction of merger of two spiral galaxies is not random because the strength of the gravitational field is different on the axis of the galaxy and in its plane of rotation. This does explain who spiral galaxies avoid most destructive mergers and also explains how galaxies can grow from the edges feeding off smaller galaxies and clumps of star in their disk plane at the edges. Problem solved.

 

[betzalel]

Angular momentum is not conserved in galaxies anyway. If it has more angular momentum than it can gravitationally constrain then it flings some of the stars on the rim off into deep space. As new objects passing through space enter a galaxy, they may be assimilated and transfer their momentum angular and otherwise to the galaxy. A galaxy is not a closed system.

Angular momentum is always conserved, in the case of interaction of galaxies. i.e. There are no significant nuclear energy sources or other energy sources to effect the interaction. The resultant reaction, final orbits, final structure after the interaction is determined by the initial velocity of the two galaxies, the angle of approach, and the masses of the two galaxies and individual stars.

Let's try to picture the difference between a spiral galaxy and elliptical galaxy.

The stars and gas in a spiral galaxy are primarily in one plane and all rotate in the same direction about the center of mass of the spiral with the exception of the stars in the spiral galaxy's bulge. The stars in the spiral galaxy's bulge revolve around the center of the mass of the galaxies in all planes and revolve in all directions the same as in an elliptical galaxy.

Simplified picture showing the Motion of stars in an elliptical galaxy

http://www.astro.utu.fi/~cflynn/galdyn/motions_random.s.gifhttps://en.wikipedia.org/wiki/Milky_Way#/media/File:Milky_way_profile.svg

8.5 10^11 Solar Masses Milky Way mass roughly have of the Andromeda Galaxy

An elliptical galaxy is a type of galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. Unlike flat spiral galaxies with organization and structure, they are more three-dimensional, without much structure, and their stars are in somewhat random orbits around the center.

Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium and minimal star formation activity, and they tend to be surrounded by large numbers of globular clusters. Elliptical galaxies are believed to make up approximately 10–15% of galaxies in the Virgo Supercluster, and they are not the dominant type of galaxy in the universe overall.[3] They are preferentially found close to the centers of galaxy clusters.[4] Elliptical galaxies are (together with lenticular galaxies) also called "early-type" galaxies (ETG), due to their location in the Hubble sequence, and are found to be less common in the early Universe

Simplified picture showing the Motion of stars in an elliptical galaxy

http://www.astro.utu.fi/~cflynn/galdyn/motions_random.s.gif

Spiral Galaxy

https://c2.staticflickr.com/4/3132/3190926961_30b795e8f2_b.jpg

https://upload.wikimedia.org/wikipedia/commons/e/e7/Phot-35d-04-fullres.jpg

Elliptical Galaxy

https://upload.wikimedia.org/wikipedia/commons/8/80/Elliptical_galaxy_IC_2006.jpg

Elliptical galaxy with a jet of matter that is 'ejected' from the galaxy

http://hubblesite.org/newscenter/archive/releases/2008/30/image/f/format/xlarge_web/

 

[Dale]

OK, this thread is closed. It is going in circles and attracting crackpots.