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Milky Way Dwarf Galaxies Thwart Newtonian Gravity?


Isaac Newton

Here at Universe Today, the subject of Newtonian gravity always seems to lead to vigorous debate. Now, there’s new research to stoke it.

Manuel Metz, and astrophysicist at the German Aero-space Center, and his colleagues say dwarf galaxies in the Milky Way are arranged in a way that precludes the existence of dark matter — but also depends on it. 

“Maybe Newton was indeed wrong,” said Pavel Kroupa, an astronomer at Bonn University. “Although his theory does, in fact, describe the everyday effects of gravity on Earth, things we can see and measure, it is conceivable that we have completely failed to comprehend the actual physics underlying the force of gravity.”

As modern cosmologists rely more and more on the ominous “dark matter” to explain otherwise inexplicable observations, much effort has gone into the detection of this mysterious substance in the last two decades, yet no direct proof could be found that it actually exists. Even if it does exist, dark matter would be unable to reconcile all the current discrepancies between actual measurements and predictions based on theoretical models. Hence the number of physicists questioning the existence of dark matter has been increasing for some time now. Competing theories of gravitation have already been developed which are independent of this construction. Their only problem is that they conflict with Newton’s theory of gravitation.

In two new studies, Metz and his team have examined so-called “satellite galaxies.” This term is used for dwarf galaxy companions of the Milky Way, some of which contain only a few thousand stars. According to the best cosmological models, they exist presumably in hundreds around most of the major galaxies. Up to now, however, only 30 such satellites have been observed around the Milky Way, a discrepancy in numbers which is commonly attributed to the fact that the light emitted from the majority of satellite galaxies is so faint they remain invisible.

A detailed study of these stellar agglomerates has revealed some astonishing phenomena: “First of all, there is something unusual about their distribution,” Kroupa said, “the satellites should be uniformly arranged around their mother galaxy, but this is not what we found.” More precisely, all classical satellites of the Milky Way – the eleven brightest dwarf galaxies – lie more or less in the same plane, they are forming some sort of a disc in the sky. The research team has also been able to show that most of these satellite galaxies rotate in the same direction around the Milky Way, like the planets revolve around the Sun.

The physicists believe that this phenomenon can only be explained if the satellites were created a long time ago through collisions between younger galaxies.

“The fragments produced by such an event can form rotating dwarf galaxies,” Metz said. But there is an interesting catch to this crash theory, “theoretical calculations tell us that the satellites created cannot contain any dark matter.” This assumption, however, stands in contradiction to another observation. “The stars in the satellites we have observed are moving much faster than predicted by the Gravitational Law. If classical physics holds this can only be attributed to the presence of dark matter.” 

Or one must assume that some basic fundamental principles of physics have hitherto been incorrectly understood. “The only solution would be to reject Newton’s classical theory of gravitation,” adds Kroupa. “We probably live in a non-Newton universe. If this is true, then our observations could be explained without dark matter.” Such approaches are finding support amongst other research teams in Europe, too.

It would not be the first time that Newton’s theory of gravitation had to be modified over the past hundred years. This became necessary in three special cases: when high velocities are involved (through the Special Theory of Relativity), in the proximity of large masses (through the theory of General Relativity), and on sub-atomic scales (through quantum mechanics). 

Source: Eurekalert. The relevant papers are available here and here.

Comments on this entry are closed.

  • Nereid May 14, 2009, 5:48 PM

    @DrFlimmer: here’s a very recent preprint in arXiv that you may find interesting, in light of your recent comments about QM, GR, etc (Title, authors, abstract):

    Atom interferometry tests of local Lorentz invariance in gravity and electrodynamics
    Keng-Yeow Chung, Sheng-wey Chiow, Sven Herrmann, Steven Chu, Holger Mueller

    We present atom-interferometer tests of the local Lorentz invariance of post-Newtonian gravity. An experiment probing for anomalous vertical gravity on Earth, which has already been performed by us, uses the highest-resolution atomic gravimeter so far. The influence of Lorentz violation in electrodynamics is also taken into account, resulting in combined bounds on Lorentz violation in gravity and electrodynamics. Expressed within the standard model extension or Nordtvedt’s anisotropic universe model, we limit twelve linear combinations of seven coefficients for Lorentz violation at the part per billion level, from which we derive limits on six coefficients (and seven when taking into account additional data from lunar laser ranging). We also discuss the use of horizontal interferometers, including atom-chip or guided-atom devices, which potentially allow the use of longer coherence times in order to achieve higher sensitivity.

    (Source: http://arxiv.org/abs/0905.1929)

    Pretty cool, eh? :-)

  • Nereid May 14, 2009, 6:41 PM

    Let’s see now …

    A. Peratt, “Evolution of the Plasma Universe: I. Double Radio Galaxies, Quasars, and Extragalactic Jets” (1986); some extracts

    In dimensionless gaussian simulation units, (9) is:
    v = Bd/2 SQRT (2L/M) (10)

    {I cannot reproduce the fonts, nor the subscripts; both are important}

    The simulations reported in this paper are scaled to Cygnus A using the latter force law via (9)


    These parameters characterize Cygnus A and are in close agreement with many previously published estimates using independent means (Table I).

    Bottom line: pace Anaconda, Peratt’s model has little room for tweaking; once the scaling laws are established and just a few parameters fixed, the results stated follow.

    Corollary: if no interacting Birkeland filaments of thickness ~35 kpc and length ~300 Mpc – 3 Gpc are observed, then Peratt’s model cannot account for “Double Radio Galaxies, Quasars, and Extragalactic Jets” (at least, not those kinds covered in this paper).

    A. Peratt, “Evolution of the Plasma Universe: II. The Formation of Systems of Galaxies” (1986); some extracts

    The evolution of cosmic plasma from a filamentary state to the development of double radio sources and quasars was investigated in the first paper […] The time frame of this study, based upon scaling simulation parameters to galactic dimensions, spanned some 10^8 – 10^9 years. In this paper (Paper II), the evolution for the next 1-5 x 10^9 years under the influence of electromagnetic forces acting on the plasma is investigated.

    Figures 3, 4, 5, and 6 are snapshots from the simulation; one of these is to be found on the website that a link Anaconda gives takes you to.

    Table II (Percentage Classification of Observed and Simulation Galaxies (Time T = 0-2000)) is quite eye-opening; in Peratt’s model, elliptical galaxies evolve into irregulars, which in turn evolve into spirals!

    And on, and on, and on … if you have kept abreast of the observational results from the likes of the HST, the VLTs, the Kecks, the Geminis, Chandra, XMM-Newton, Spitzer, GALAX, 2MASS, … – none of which were available in 1986 – you’ll no doubt find the Peratt papers amusing, astonishing, even incredible (no wonder just about the only person who cites these is Peratt himself).

  • DrFlimmer May 15, 2009, 4:01 AM


    (Source: http://arxiv.org/abs/0905.1929)

    Pretty cool, eh? :-)

    Very cool, indeed :-)


    Science does know there are large extraglactic magnetic fields (having underlying electric currents which generate the magnetic fields).

    This is likely true, but you should tell the whole story: Those “large” magnetic fields are probably of extream dimensions, but they tend to be really weak. Even the earth’s magnetic field is quite weak and the interstellar is even weaker. The only thing the earth’s magnetic field is doing is protecting us (which is, of course, a good thing) from cosmic rays (including the solar wind). It is of no further use (yes, it was used for navigation in the past…) and is doing anything that we could call “important”.
    What I mean is that the weak magnetic field of our planet isn’t doing much. The magnetic field in interstellar and intergalactic space is even weaker. I don’t think it is reasonable that such a weak thing (that is doing almost nothing on earth, the only place where we can do “real” experiments) has a more significant role than gravity.
    And I want to come back to one of your favourite formulations:

    the gravity “only” model

    Get real, dude! “modern” astronomy is far beyond that point. EM-forces are taken into account for almost any model concerning almost any problem in astrophysics. Star formation, e.g. A cold (neutral…) cloud collapses due to some external pressure (a SN, e.g.). So far so good. But finally the star heats up and its particles will become ionized. So we will gain em-fields due to the rotation. And this fields are quite necessary to explain how the star loses its angular momentum and how it can still accrete matter, although its wind is quite strong.
    How does this happen? The magnetic field “grapples” packages of matter from the inner part of the accretion disk. Those packages crash into the star and this can be seen as a “hot spot”, a bright part on the stars surface that rotates in and out of view. And guess what: We see such hot spots. We can detect them with our telescopes!
    Herbig-Haro objects are another example. It is a jet-phenomenon of young stars, a small counterpart of the big evil jets of AGN.
    So, astronomy includes em-forces, as it includes the weak force and the strong force whenever it is necessary.

    So, do me a favor, and leave out this, indeed misleading term “gravity only”. This just wrong.

  • Nereid May 15, 2009, 7:27 AM

    @DrFlimmer et al.

    @ ND (and others)

    Anaconda is also busy at the “new mysteries on mercury” thread where the debate is still going on and where I recently tried to give him some insights into quantum mechancis (which also discredits as being mathematical…). Also Nereid is doing good work over there in an attempt to come to conclusions with Anaconda.

    Not any more … it seems that thread is closed to comments now; a sign, perhaps, that I should abandon my attempts to find a mutually agreed basis on which to build a meaningful discussion with Anaconda?

  • DrFlimmer May 15, 2009, 9:52 AM

    No, but a sign that we broke some of the rules….. Our posts tended to be a bit lengthy 😉

  • Nereid May 15, 2009, 10:07 AM

    Well, if that’s the only thing, then easily addressed; instead of one comment of x words, write n comments each with an average of x/n words …

    (somehow I think there’s more to it than that)