Another MOND prediction confirmed.

[ohwilleke]

http://uk.arxiv.org/abs/astro-ph/0504051

Date: Sun, 3 Apr 2005 10:51:05 GMT (4kb)

Testing MOND with Ultra-Compact Dwarf Galaxies
Authors: Riccardo Scarpa
Comments: Two pages. Submitted for publication to MNRAS

The properties of the recently discovered Ultra-Compact Dwarf Galaxies (UCDs) show that their internal acceleration of gravity is everywhere above a0, the MOdified Newtonian Dynamics (MOND) constant of gravity. MOND therefore makes the strong prediction that no mass discrepancy should be observed for this class of objects. This is confirmed by the few UCDs for which virial masses were derived. We argue that UCD galaxies represent a suitable test-bench for the theory, in the sense that even a single UCD galaxy showing evidence for dark matter would seriously question the validity of MOND.

But, in the other direction we have:

http://uk.arxiv.org/abs/astro-ph/0503104

Date: Fri, 4 Mar 2005 18:18:46 GMT (161kb)
Date (revised v2): Fri, 4 Mar 2005 21:24:13 GMT (162kb)

Does VIRGOHI21 pose a problem for MOND?
Authors: Scott Funkhouser
Comments: 1 page. 2nd version has minor formatting and wording improvements

If the inferred parameters of the recently discovered dark galaxy VIRGOHI21 are verified then the dynamics of the body may represent a counter-example to the accelerations predicted by MOND.

This involves the so called "dark galaxy" and contains the caveat that the measurements are not yet considered definitive.

And, for all around MOND/TeVeS junkies, we have one of the first really serious critiques of Bekenstein's proposed relativistic modified Newtonian dynamics theory called TeVeS:

http://uk.arxiv.org/abs/gr-qc/0502122

Date (revised v2): Wed, 27 Apr 2005 13:58:24 GMT (15kb)

Spherically symmetric, static spacetimes in a tensor-vector-scalar theory
Authors: Dimitrios Giannios
Comments: 12 pages, accepted for publication in Phys. Rev. D

Recently, a relativistic gravitation theory has been proposed [J. D. Bekenstein, Phys. Rev. D {\bf 70}, 083509 (2004)] that gives the Modified Newtonian Dynamics (or MOND) in the weak acceleration regime. The theory is based on three dynamic gravitational fields and succeeds in explaining a large part of extragalactic and gravitational lensing phenomenology without invoking dark matter. In this work we consider the strong gravity regime of TeVeS. We study spherically symmetric, static and vacuum spacetimes relevant for a non-rotating black hole or the exterior of a star. Two branches of solutions are identified: in the first the vector field is aligned with the time direction while in the second the vector field has a non-vanishing radial component. We show that in the first branch of solutions the \beta and \gamma PPN coefficients in TeVeS are identical to these of general relativity (GR) while in the second the \beta PPN coefficient differs from unity violating observational determinations of it (for the choice of the free function $F$ of the theory made in Bekenstein's paper). For the first branch of solutions, we derive analytic expressions for the physical metric and discuss their implications. Applying these solutions to the case of black holes, it is shown that they violate causality (since they allow for superluminal propagation of metric, vector and scalar waves) in the vicinity of the event horizon and/or that they are characterized by negative energy density carried by the fields.

I'd also welcome comments on this article:

http://uk.arxiv.org/abs/astro-ph/0412415

Date: Thu, 16 Dec 2004 12:51:30 GMT (18kb)

Via Aristotle, Leibniz & Mach to a relativistic relational gravity
Authors: D F Roscoe
Comments: 18 pages, no figures, under review CQG

In previous work we have shown how a worldview that has its origins in the ideas of Aristotle, Leibniz and Mach leads to a quasi-classical (that is, one-clock) metric theory of gravitation (astro-ph/0107397) which, for example, when applied to model low surface brightness spirals (astro-ph/0306228), produces results that have, hitherto, only been matched by Milgrom's MOND algorithm. In this paper we show how the natural generalization of this worldview into a properly relativistic two-clock theory, applied to model a spherically symmetric gravitational source, produces results that cannot be distinguished from the canonical picture for all the standard local tests and which, when interpreted as a radiation model, produces no dipole radiation. Furthermore, although black-holes within this picture have an event horizon at the usual Schwarzschild radius, they do not have an essential singularity at the origin - the solutions are perfectly regular there.

which has something of a cranky alert feeling to it. This probably has something to do with the fact that Roscoe is a co-author of a paper with Arp:

http://uk.arxiv.org/abs/astro-ph/0501090

Date: Thu, 6 Jan 2005 10:24:00 GMT (812kb)

Periodicities of Quasar Redshifts in Large Area Surveys
Authors: H. Arp, C. Fulton, D. Roscoe
Comments: 23 pages, 14 figures

We test the periodicity of quasar redshifts in the 2dF and SDSS surveys. In the overall surveys redshift peaks are already apparent in the brighter quasars. But by analyzing sample areas in detail it is shown that the redshifts fit very closely the long standing Karlssson formula and strongly suggest the existence of preferred values in the distribution of quasar redshifts.
We introduce a powerful new test for groups of quasars of differing redshifts which not only demonstrates the periodicity of the redshifts, but also their physical association with a parent galaxy. Further such analyses of the large area surveys should produce more information on the properties of the periodicity.

 

[Chronos]

More Arp pseudo-science. I assume I will be asked why I think it's a cowpie.

 

[Nereid]

More Arp pseudo-science. I assume I will be asked why I think it's a cowpie.

Why do you think it's cowpie, Chronos?

 

[turbo]

I'd also welcome comments on this article:

http://uk.arxiv.org/abs/astro-ph/0412415

Interesting approach, but I think it's too literally Machian, and suffers from the lack of a "nuts and bolts" mechanism. Note: In my ZPE model, radiational anisotopies are expected, due to our motion through the vacuum fields. I believe that these motions are the cause of the symmetrical anisotropies that are seen in the WMAP data. When WMAP2 is released, we will know if this concept is correct, or it least we will know if it is flatly falsified.

 

[Chronos]

Why do you think it's cowpie, Chronos?

Surely you jest. Perhaps because of stunning assertions like:

For over 35 years now the evidence has been building for a set of numerically defined peaks in the distribution of quasar redshifts - the so-called Karlsson peaks. But the existence of the Karlsson peaks has generally not been acknowledged - primarily because of the serious implications for canonical cosmology.

I could not have said it better: the so-called Karlsson peaks. Indeed. No doubt that has serious implications for canonical cosmology.:rofl:

And this is priceless:

The purpose of the present paper is not to address their criticism of past evidence (that has been done by Napier and Burbidge, 2003, who show the past evidence is indeed valid) - but rather to show that, also contrary to the Hawkins et al. claim, a simple qualitative analysis of the new data plus a detailed analysis of a few sample fields, reveals that quasar periodicity is indeed strongly present.

 

[ohwilleke]

Rather than clutter up a new thread, I'll note some observations from an exceptionally long, for Science News, April 23, 2005 Science News Article on Dark Matter: http://www.sciencenews.org/articles/20050423/bob9.asp

From the article:

Because dark matter doesn't appear to be affected by any force other than gravity, computer simulations indicate that all the halos should be similar—roughly spherical and much denser at their cores than at their edges. . . .Now, having obtained the highest-resolution observations yet of motions within galaxies, Joshua D. Simon of the University of California, Berkeley and his colleagues seem to have settled the question. . . .By measuring the clouds' speeds and factoring out the influence of visible matter, the scientists measured the density of the dark matter halos at various distances from their centers. One halo was densely packed toward the galaxy's center, as simulations predicted, another had a density that was the same everywhere, and the density profiles of the other three were somewhere in between these extremes.

Astronomers aren't sure how to explain this variety. One possibility is that dark matter responds to forces other than gravity. If dark matter particles can collide with each other, for example, then they might avoid getting crowded together near the centers of galaxies, despite gravitational attraction. Another possibility is that ordinary matter, the kind that emits or absorbs light, can somehow alter the distribution of the dark matter.

Such distinctions fall naturally out of MOND theory. And, of course, the whole point of dark matter is to have to avoid inventing a new fundamental force, and another study mentioned in the article casts doubt on the collision theory. So, the means for resolving the discrepency between theory and reality are limited.

The variety of halo structures isn't the only problem that makes some astronomers wonder whether there's real substance to the notion of dark matter. For years, astronomers have scratched their heads over a second problem: a shortage of the smallest dark matter halos.

"Despite its spectacular successes, [the standard theory of] dark matter has had these two big problems," says Priyamvada Natarajan of Yale University.

Astronomers have detected halos of different sizes, and they suspect that the larger halos form through the mergers of smaller ones. Computer simulations of this process match the observed range of sizes, with the exception of the smallest halos within which tiny galaxies, called dwarf galaxies, form. In vast orbits around our own medium-size galaxy, astronomers have found about a dozen of these dwarfs, but simulations of dark matter predict there should be 50 or so dwarfs around the Milky Way.

As the article on UCDs cited above explains, that isn't a problem for MOND.

If dark matter particles can collide and interact, these processes should be reflected in the distribution of dark matter on larger scales. Dense clusters containing hundreds or thousands of galaxies would be surrounded by a very large dark matter halo, in which smaller halos associated with each galaxy would be embedded. In such a cluster, collisions between dark matter particles should eventually erase boundaries demarcating the smaller halos. . . .Using Hubble Space Telescope images taken for earlier studies, Natarajan looked at how relatively nearby clusters of galaxies bend the light of distant galaxies. By subtracting the lensing effect of the ordinary matter, Natarajan's team zeroed in on the portion of lensing due to dark matter. In this way, the team mapped out, in unprecedented detail, where the dark matter lies in these clusters.

"No one's ever been able to do this kind of detailed, high-resolution study" of dark matter distribution in clusters, she says. The analysis revealed lots of galaxy-size clumps of dark matter within the overall cluster halo, so the boundaries haven't vanished.

This finding rules out the idea that dark matter particles can collide and interact with one another, Natarajan contends.

In short, even though the Science News article doesn't question for a moment the fundamental premise of dark matter theory, it does point out significant collisions between dark matter theory and observed reality.

 

[x8jason8x]

being a newbie to your forums, and especially not having any letters after my name, I tread carefully here. This theory seems to beg the age old question of the tree falling in the forest, as far as I can tell. What ramifications does this have toward MOND, if proved or disproved?

 

[ohwilleke]

FWIW, the letters I have next to my name (J.D. and Esq.) don't rate much in these forums either.

The basic issues are these:

(1) The model of general relativity applied to only luminous matter fails dismally. It can't even explain the dynamics of the Milky Way, or for that matter, most galaxies and galactic clusters and large scale structure which we observe.

(2) It follows that general relativity is wrong, or that there is more stuff than luminous matter out there, or both.

(3) The leading theory arguing that general relativity is wrong is called MOND, although it has advanced cousins (with names like TeVeS) and theoretical cousins (like Conformal Gravity). The leading theory arguing that there is invisible stuff is the Lambda Cold Dark Matter theory. It also has cousins (like Warm Dark Matter).

(4) In the "easy cases" like the dynamics of plain vanilla spiral galaxies, the two theories tend to predict the same thing. Indeed, finding predictions that differ between CDM and MOND is sometimes a challenge. But, knowing which is right does help in dealing with the "hard cases".

(5) If the main CDM theory is correct, then we really need to discover what 90% of the matter in the universe is made out of. The leading candidates are WIMPs (often assumed to be axions or neutralinos, two types of particles not in the Standard Model of Particle Physics). We also need to figure out why dark matter distributes itself in the manner in which it does.

(6) If the underdog MOND theory is correct, then mainstream cosmologists have egg on their face because they widely stated that there was lots of dark matter out there that doesn't exist. (MOND basically argues that very weak gravitational fields are stronger than predicted by Newtonian gravity and GR which are virtually identical in these situations, except for lensing).

(7) MOND has the virtue of being a more tightly constrained theory. It has fewer free parameters. Thus, it usually makes more definitive predictions. For example, MOND says that UCD galaxies are going to have no dark matter effects, while low surface brightness galaxies will have strong dark matter like effects. In contrast, CDM theory requires a whole lot of subtheories to figure out what sort of dark matter halo can be expected from a particular type of galaxy or galactic superstructure.

(8) MOND could also shed light on quantum gravity. One possible reason that it is hard to merge GR and quantum physics is that the GR equations we are trying to merge into quantum physics are wrong, and that MOND is a manifestation of subtle differences between a quantum physical version of gravity and a classical theory of gravity in GR.

Of course, like almost all questions in astronomy, practicality is a secondary consideration. Nobody is going on transgalactic space flights anytime soon (well, except for Arthur Dent and Ford Prefect) and the predictions of cosmology about the beginning and end of the universe are billions of years in the past and future. Moreover, even if we perfectly understood quantum gravity, there is no good reason to believe that we could apply that knowledge in any useful way (other than making better star charts).

 

[matt.o]

Here is a nice paper describing the descrepancy between observed dynamical masses and MOND masses in clusters of galaxies:

http://arxiv.org/abs/astro-ph/0505017

New constraints on MOND from galaxy clusters
Authors: Etienne Pointecouteau, Joseph Silk
Comments: 5 pages, 1 figure, MNRAS submitted

We revisit the application of Modified Newtonian Dynamics (MOND) to galaxy clusters. We confront the high quality X-ray data for eight clusters of galaxies observed by the XMM-Newton satellite with the predictions of MOND. We obtain ratios of the Newtonian dynamical mass to the MOND mass of M_d/M_m=1.09+/-0.08 at r~0.1 R_vir increasing to M_d/M_m=1.57+/-0.24 in the outer parts (i.e r~0.5 R_vir), in the concordance cosmological model. We confirm that the MOND paradigm lowers the discrepancy between the binding mass with the baryonic mass in clusters to a factor of ~1.6 at about half the virial radius, that as pointed out by Sanders (2003), necessitates a component of dark baryons or neutrinos in the cluster core. However application of the new data requires a much larger discrepancy of ~4.5 (increasing to 5.1 when only hot systems are considered, i.e kT>3.5keV) at large radii that MOND cannot explain without introducing further ad hoc assumptions.

 

[ohwilleke]

The Pointecouteau and SIlk paper and the study of galactic clusters in the Science News article make clear that neither conventional CDM theory, nor MOND has the whole picture in galactic clusters.

It was noted early on that "naiive MOND", i.e. the basic point source formula with gravity strengthened beyond a critical graviational field strength doesn't work in less symmetric situations (as it leads to non-conservation of energy, etc.). Given that galaxies apparently do have fairly distinct gravitational signatures distinct from the Newtonian visible matter signatures within clusters, it seems to me that this is likely to be a case where the full blown GR generalized (or at least Lorenzian) formulation is necessary to get a good result.

 

[ohwilleke]

Read the Silk paper some more. It does take into account TeVeS to some extent. Among the interesting finding are: (1) discrepencies appear to be higher where cluster temperatures are higher, (2) discrepency values vary quite a bit, (3) there are no underestimates of the amount of matter.

The big question from the mind of a MOND theorist for some time has been: Why should galactic clusters behave differently when everything else in the universe seems to fit the theory? What is special about clusters?

Sanders took a stab at it and guessed that there was a surplus of massive neutrinos. Others have guessed that there is a non-linear mass relationship (cube rootish) but that doesn't seem to fit results at other scales. Lack of spherical symmetry within a cluster is another possible factor.

The notion that hot clusters should have more of a discrepency than cold ones is suggestive of the idea of the energy in the system gravitating in addition to the matter. Still, it is a basically unanswered question.

 

[Chronos]

We should have some kind of answer [which might be none of the above] by the end of this decade. If there is another threshold of particle energies, you would think it will surely show up when the LHC goes on line.

 

[turbo]

We should have some kind of answer [which might be none of the above] by the end of this decade. If there is another threshold of particle energies, you would think it will surely show up when the LHC goes on line.

Regarding particle energy thresholds: The Standard Model assumes that there is a particle - the Higgs Boson - that mediates gravitational forces, and it was expected to reside at energies of 80 GeV. LEP failed to detect it, even at 115 GeV. The faithful simply shrug and say "the Higgs Boson exists at a higher energy than we expected and the LHC will find it".

I believe that negative results are just as critical to our understanding of physics as positive results - that is the nature of experimentation. This real value can only be realized, however, if theorists are willing to accept the results of observation. If the theorists are so in love with their theories that they will constantly tweak and massage them to conform with discordant observations, we will end up with ugly, kludged, Gordian-knot explanations of our U that become more constrained and less useful with every epicycle. Sound familiar?

 

[ohwilleke]

We should have some kind of answer [which might be none of the above] by the end of this decade. If there is another threshold of particle energies, you would think it will surely show up when the LHC goes on line.

The LHC might very well turn up new particles -- although I wouldn't put good money on it. Certainly, current theory predicts that it could prove the existence of a Higgs boson, an axion or a neutralino, all of which are prime WIMP/CDM candidates. Of course, turbo-1 is entirely correct when he notes that if LHC doesn't find anything that the theorists will go back to the drawing board and figure out why the predicted mass of those candidates was too low.

But, as the Science News article notes, the bigger problem is that DM theory does as poor of job of explaining why apparent DM is distributed in the manner that it is in galactic clusters, as MOND does at explaining why its theory doesn't make all the missing mass go away.

 

[matt.o]

No, dark matter fits observations on a cluster scale very well. MOND doesn't. Dynamical temperatures derived assuming dark matter agree very well with x-ray temperatures, as do mass estimates (from dynamics, xray observations and gravitational lensing) . Clusters seem to show a good fit to NFW dark matter profiles. This is why they are such a thorn in MONDs side.

 

[ohwilleke]

See post #6 above. The third blockquote explains that experiment is inconsistent with colliding dark matter. But, in the absence of collisionful dark matter, there is no explanation for observed halo structure as noted in the first blockquote in that post.

 

[matt.o]

Ok, so dark matter fits observations on a cluster scale, but not as well on a galactic scale. You are talking about the smaller scale halos residing within the cluster dark matter halo. I ws talking about the cluster dark matter halo.