I don’t spend too much time worrying about the ultimate fate of the Earth as it interacts with a swollen red Sun some five billion years from now. My thought is that if any civilization is still on the planet in a billion years, it will have long since worked out how to exit when necessary (and it will be necessary a lot sooner than five billion years!), or maybe how to tweak planetary orbits to preserve our planet, if only as a choice historical site.
Still less do I worry about the Milky Way being destroyed by a collision with one or more satellite galaxies, like the Large and Small Magellanic Clouds that move around the parent galaxy. So when I read that an Ohio State team led by Stelios Kazantzidis had shown via computer simulations that such a collision would leave the galaxy more or less intact, my real interest was in the implications of this work in terms of one of science’s great mysteries — the nature of dark matter. Have a look at the team’s modeling of the dark matter structure thought to surround galaxies like ours.
Image: This image from a supercomputer simulation shows the density of dark matter in our Milky Way galaxy which is known to contain an ancient thin disk of stars. Brightness (blue-to-violet-to-red-to-yellow) corresponds to increasing concentration of dark matter. The bright central region corresponds roughly to the Milky Way’s luminous matter of gas and stars and the bright clumps indicate dark-matter satellites orbiting our Milky Way galaxy which are known as “substructure”. The simulation predicts that the dark-matter halos of spiral galaxies are lumpy, filled with hundreds of dark matter substructures that pass through the stellar disks of galaxies, leaving their imprint and disturbing them in the process. Credit: Stelios Kazantzidis, Ohio State University.
If galaxies are embedded within huge haloes of dark matter (the Milky Way’s halo is thought to be a million light years across, or ten times larger than the 100,000 light year width of the galaxy), then a filamentary model of dark matter running throughout the universe emerges, with the larger galaxies at the intersection of dark matter filaments. As this Ohio State news release suggests, satellite galaxies like the Magellanics would move along the strands of this web, gradually drawn into orbit around the larger galaxies.
Kazantzidis’ team ran computer simulations of galaxy formation to study this model, setting up collisions between satellite galaxies (and their associated dark matter) and the larger spiral galaxy. During the collision, the dark matter interacts gravitationally with the spiral galaxy. The result: The satellites pass through the galactic disk again and again, losing mass each time. The effect of their gradual dissolution is that the primary galaxy shows a distinctive signature that is consistent with observation.
Says Kazantzidis:
“We can’t know for sure what’s going to happen to the Milky Way, but we can say that our findings apply to a broad class of galaxies similar to our own. Our simulations showed that the satellite galaxy impacts don’t destroy spiral galaxies — they actually drive their evolution, by producing this flared shape and creating stellar rings — spectacular rings of stars that we’ve seen in many spiral galaxies in the universe.”
The next figure shows the formation of this unique flared shape:
Image: Density maps of disk stars illustrating the global morphological transformation of a galactic disk subject to bombardment by dark matter substructures. Brighter colors indicate regions of higher density of disk stars. The left panel shows the initial disk, while the right panel depicts the final disk after the violent gravitational encounters with the orbiting substructures. The edge-on (upper panels) and face-on (bottom panels) views of the disk are displayed in each frame. Satellite-disk interactions of the kind expected in the currently favored cosmological model produce several distinctive signatures in galactic disks including: long-lived, low-density, ring-like features in the outskirts; conspicuous flares; bars; and faint filamentary structures above the disk plane that resemble tidal streams. These morphological features are similar to those being discovered in the Milky Way, the Andromeda galaxy, and in other spiral galaxies. Credit: Stelios Kazantzidis, Ohio State University.
So we have what Kazantzidis calls ‘a wealth of signatures’ that are both consistent with the current cosmological model (including dark matter) and consistent with observations of other galaxies. The flared edges of the above image, in which a disk that is narrow at the center widens toward the edges, are such a signature. The latest report on this work is in Kazantzidis et al., “Cold Dark Matter Substructure and Galactic Disks. II. Dynamical Effects of Hierarchical Satellite Accretion,” Astrophysical Journal 700 (2009), pp. 1896-1920 (abstract). A preprint is also available.
Hi Paul;
The graphic of the numerical simulation of dark matter galactic dynamics is beautiful. It is an honor to live in an age where computational models permit such detailed and fine scaled resolutions of systems having the massive and spatial temporal extent of galaxies with such precision.
We humans have come a long way since our hunter gatherer hominid ancestors and I must say I am duely impressed with the technological and scientific prowess of our species. The fact that we have the where-withall to perform such numerical simulations with the full brunt of the logical rigor and precision that is commensurate with the deliberative, rational, and cerebral nature of computer code writting tells me that we have the where-with-all to develope interstellar travel systems.
We developed the atomic bomb in a few short years in the crash course of the Manhattan Project. We can probably develop a manned star-ship in fairly short order especially if some bold national. multi-national, or global UN style mandate was agreed upon and the funds were provided to develope mission scenarios, and the flight hardware and software controls required for a manned star ship.
Some of my significant others as well as others I know have often stated that astronomy is easy and is a kind of non-technical and non-rigorous scientific discipline, to which I have long since tired of arguing to these individuials that, “No Astronomy is not a soft headed science! Astronomers and astrophysicists use supercomputers to model every thing from supernova, planetary formation, to galaxy dynamics and the evolution of the universe.”
Reading your above article has inspired me all the more to want go back to school for further studies in related fields in addition to but not in substitution to my real heart felt vocation to be a practicioner of Tau Zero.
James, if Ithink you need to develop a more skeptical attitude to computer models. I had the opposite reaction to you, I thought this is just too good to be true !
Keith, I’m with you. I’ve been doing independent research in Galactic Astronomy for 3 years now and I find that, despite the litany of proclaimed successes for the CDM paradigm in various specialized fields, it does not cohere with general observations.
Computer simulations of CDM also… 1) predict that CDM particles ought to coalesce to peak densities in galactic cores; however, the observational evidence of star dynamics at inner galactic radii of many galaxies, including our own Milky Way, indicate that these galactic cores are entirely devoid of CDM. No valid mechanism has been demonstrated to account for how galactic cores are swept clean of CDM. This is known as the “cuspy halo problem.”… 2) CDM models applied to cosmology predict that an abundance of small satellite galaxies ought to be orbiting large galaxies like the Milky Way; however, the number of Milky Way satellite objects discovered so far, even after the advent of very advanced digital sky surveys like SDSS, is still ~100 times less numerous than predicted. … 3) The same application predicts that a vast majority of such satellite galaxies ought to be objects that have been formed in intergalactic space and subsequently captured by the Milky Way; however, the satellite galaxies that are known tend to be located near the plane of the Milky Way, orbiting the Galaxy in same direction as Galactic rotation, which suggest that these objects convolved with the Milky Way.
My own prediction? CDM will be completely abandoned within ten years.
Thanks Erik. My own feeling about this work was not based on anything so logical, just a thought that it was just too neat for the pictures to have come out so good. It’s very time consuming for an independent referee to go through someone else’s code, which has taken months to put together, and find all the little tweaks. I just bet that all kinds of little arbitrary tweaks and adjustments to numbers have been put it just to make the output look the way they wanted.
yes!!!!!!!!!!! if we are around that far in the future we WILL have long since worked out how to survive. how? considering the exponential growth of science you just about name it that far in the future! everything from escaping into a parallel dimension to “moving” to a new galaxy! thank you all your friend george
Does anyone get the same underlying bad feeling that dark matter will not be found, perhaps ever, because it is not there to be found? Alas, with each passing year this feeling grows stronger within me. I would like resolution–that is, I would like it if we just found the stuff. It would put not only cosmology but also physics on a firmer footing (because it would confirm our understanding of gravitation) and we would of course have the satisfaction of knowing what makes up a ~ 1/4 of the entire Universe.
Keith: I know what you mean. Johnny von Neumann reputedly used to say that with four arbitrary parameters he could model an elephant — with five he could make the elephant wiggle his trunk.
N-body simulations have not been very successful in modeling galactic evolution. Transient features such as spirals and rings may appear and disappear spontaneously, like in the above example, but they do not ~endure~ like they do in real galaxies — so it’s not entirely fair to exhibit snapshots as if they represented final states.
Atomic matter such as hydrogen gas and molecular clouds must also play a critical role in shaping and maintaining galactic structure — a feature that N-body modelers usually miss and/or can’t deal with.
spaceman: with me “it’s more than a feeling” (as the popular Boston song goes) that Cold Dark Matter is completely fictional (as you may have already discerned from my previous comments). I believe that CDM will indeed never be found, just as the quest for “ether” in the 19th century fell flat on its face in the wake of the new reality of Einstein’s Relativity.
The presence of CDM in galaxies, we must remember, is wholly predicated upon measurements of radial velocities inferred from Doppler shifts seen in spectrographs of starlight — velocities which have not been empirically validated by independent means. The tools we need to do so are forthcoming, however. ESA’s Gaia mission, for example, will extend the reach of useful ~astrometric~ measurements (sky positions, angular motions, and parallaxes) to unprecedented distances. I then expect that systematic errors in spectroscopic radial velocities will be unequivocally demonstrated. Once these errors are exposed, the LCDM paradigm (dark energy + cold dark matter) will fall like a house of cards.
Erik: the original case for non-baryonic CDM was based simply on galactic rotation curves. All this other stuff arrived later.
Now, you say that the velocities are from ‘spectrographs of starlight’. If you’re talking about galactic rotation curves, I’m not sure this is strictly true. As I understand it, the curves are based on radioastronomy of the HI (hydrogen gas) regions.
There is a theory that the rotation curves, so derived, are an artefact of this measurement process. The theory says that outer HI regions are more under the control of the galaxy’s magnetic field than its gravity. The magnetic field is sweeping the outer gas areas along much faster than is required simply by gravity, thereby giving the illusion that much more mass is required. I’m not sure how tenable this theory is, do you have any thoughts?
Hi Keith,
You are correct. Galactic rotation curves are regularly derived from radio spectrographs of ionized gas as well as optical spectrographs of stars. For the systematic effect I’m describing, it doesn’t matter where in the e.m spectrum the measurements are undertaken. The error has a cosmic origin and it grows primarily in proportion to the size of the orbit of the emitting body. This is why galactic rotation curves ~look~ like they have MONDian components — hence why MOND ~seems~ to work so well at galactic scales, but fails at super-galactic scales.
I do vaguely recall reading a conjecture that magnetic fields channel galactic gas motions. It suspect the idea may be naive.
My own involvement in galactic research has lent support to the more elegant idea that gas motions follow orbital trajectories similar to stars, and that such orbits cross over at the locations of spiral arms. At these orbital intersections, stars will shoot past each other, but gases will collide, increasing density to the point of creating star formation regions. If you look at the Hubble image of the Whirlpool Galaxy (M51), for example, it may be plainly observed that the inside edges of the spiral arms are distinctively dark (where colliding gas has thickened into opaque clouds) and the outside edges are distinctively bright (where freshly minted stars have ignited).
More about all this here: http://rqgravity.net/SpiralStructure
CDM, although still the dominant paradigm for structure formation, is gradually falling out of favor. I’ve been following cosmology for the past ten years and I have definitely noticed, upon perusing presentation titles for cosmology conferences, an increase in the number of presentations discussing non-CDM theories such as MOND, MOG, and TeVeS relative to dark matter presentations (tho I have not yet completely my statistical analysis of this trend). A trend is developing away from dark matter. No convincing evidence seems to exist that dark matter is real and the deficiencies of the theory are sorta swept under the rug. But this next decade, I agree, will be make or break for CDM. Will be interesting to see how it plays out with all of the new telescopes and detectors coming online.
Thanks for the link. I doubt I can understand all the arguments in there, and skim-reading it, I’m a bit alarmed by this transmission connection thingy, but apart from that it looks like a theory that ought to be taken seriously. It certainly looks like it can explain a good deal of paradoxical observations without resorting to inventing new forms of matter or new gravitational laws.
The AMIDAS Website: An Online Tool for Direct Dark Matter Detection Experiments
Authors: Chung-Lin Shan
(Submitted on 8 Sep 2009)
Abstract: Following our long-term work on development of model-independent data analysis methods for reconstructing the one-dimensional velocity distribution function of halo WIMPs as well as for determining their mass and couplings on nucleons by using data from direct Dark Matter detection experiments directly, we combined the simulation programs to a compact system: AMIDAS (A Model-Independent Data Analysis System).
For users’ convenience an online system has also been established at the same time. AMIDAS has the ability to do full Monte Carlo simulations, faster theoretical estimations, as well as to analyze (real) data sets recorded in direct detection experiments without modifying the source code. In this article, I give an overview of functions of the AMIDAS code based on the use of its website.
Comments: 4 pages, to appear in the proceedings of the 17th International Conference on Supersymmetry and the Unification of Fundamental Interactions (SUSY09), Boston, USA, 5-10 June, 2009
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics – Phenomenology (hep-ph)
Cite as: arXiv:0909.1459v1 [astro-ph.IM]
Submission history
From: Chung-Lin Shan [view email]
[v1] Tue, 8 Sep 2009 11:19:59 GMT (30kb)
http://arxiv.org/abs/0909.1459
On the nature of the Milky Way satellites
Authors: Yang-Shyang Li (1), Gabriella De Lucia (2), Amina Helmi (1) ((1) Kapteyn Astronomical Institute, Groningen, (2) INAF, Trieste)
(Submitted on 7 Sep 2009)
Abstract: We combine a series of high-resolution simulations with semi-analytic galaxy formation models to follow the evolution of a system resembling the Milky Way and its satellites. The semi-analytic model is based on that developed for the Millennium Simulation, and successfully reproduces the properties of galaxies on large scales, as well as those of the Milky Way.
In this model, we are able to reproduce the luminosity function of the satellites around the Milky Way by preventing cooling in haloes with Vvir 10 Gyr, and a few of them formed most of their stars before the reionization was complete.
Objects with luminosities comparable to those of the classical MW satellites are associated with dark matter subhaloes with a peak circular velocity $\gta$ 10 km/s, in agreement with the latest constraints.
Comments: 18 pages, 15 figures, Submitted to MNRAS
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:0909.1291v1 [astro-ph.GA]
Submission history
From: Yang-Shyang Li [view email]
[v1] Mon, 7 Sep 2009 17:43:11 GMT (135kb)
http://arxiv.org/abs/0909.1291
Couple of things to keep in mind regarding explaining away CDM. First, the few MOND/MOG models I’ve looked at are little more than mathematical curve fitting, generally formed by patching together several distinct functions for the gravitational force at arbitrary values of r (separation distance), with purely hypothetical “principles” as an attempt to explain the curious math. These r values only seem to work in the present epoch, not in earlier ones when galaxies were closer together, especially at the earliest time when GR effects were dominant, thus making a mess of galactic evolution models. Second, CDM is based not only on intra-galactic motion, but also among galaxies that are gravitationally bound (clusters) and gravitational lensing by galaxies and clusters.
Attempts to find sufficient CDM in the form of conventional matter (gas and MACHOs) are inconclusive or negative. The evidence for weakly-interacting CDM (especially WIMPs) fits the data better. There are ongoing attempts to directly detect WIMPs, so hopefully that will shed some light on the matter (pun intended).
Ron S,
Could you give reference(s) to MOND’s failings at earlier epochs?
Another strike against MONDian analyses is that sometimes galactic inclinations are arbitrarily fiddled with in order to get good fits.
WIMPs always fit the data best because hypothetically undetectable particles have unlimited wiggle room — their distributions can be arbitrarily constructed to custom-fit any astrodynamical or lensing situation. This aspect makes WIMPs the most difficult theory to falsify — but not the most credible.
Erik,
Regrettably, no. Since I only peruse these papers for ‘amusement’, I tend to skim or read, and then discard, keeping no records. This of course makes it difficult to have a discussion with references, so I can understand if you doubt my recollections.
Even so, look at it this way. The earlier MOND papers I remember typically had two patched functions, with standard gravitation at small r, and the modified version becoming dominant at r much greater than the size of the solar system but much less than a galactic radius. Then I saw at least one paper more recently that patched in a third function for r much greater than a galactic radius. The latter accommodated the measurements which indicated that inter-galactic dynamics appeared consistent with standard gravitation theory.
Modeling of the early universe shows a sensitivity to the tiny inhomogeneities of matter distribution that seed galaxy formation. A 3-step MOND function means that the universe, and those inhomogeneities are subject to significant variation in the gravitational force as it expands in its earliest history. I don’t know of any model that takes this into account, but rather use standard theory to (reasonably) successfully develop their finely-tuned models. There is still room for surprises due to uncertainties in the models, as Paul referenced in this recent article:
https://centauri-dreams.org/?p=9292
Regarding WIMPs, I think you’re being unfairly dismissive in your criticism. What is hard to “wiggle” out of is the observed mass of galaxies and clusters due to their relative motions and lensing action. The distribution of this CDM, whatever it is, indicates that it is weakly interacting since otherwise it would clump more like ordinary matter. Not knowing what it is does not make it pixie dust (to steal a phrase from andy). Its distribution and weak interactions make detection very difficult, especially with only vague theoretical predictions of its characteristics. It is falsifiable, though difficult. Neutrinos once posed similar difficulties, except that we fortunately have enough of a local supply to make detection possible, with enough effort.
Hi Ron,
I don’t necessarily doubt your recollections — it’s just that I hadn’t heard of this criticism of MOND before and I hope to find out what the details are. Being that I believe that CDM and MOND are false alternatives, I’m just as keen to learn about problems with MOND as much as about problems with CDM.
I agree with your assessment that the interpolation function(s) in MOND is a total kludge.
I have commented on the galaxy @ z=6.43 article as well. I take this to be problematic for Dark Energy — the other shoe of the L-CDM paradigm.
We have to be mindful of that the “observed” mass of galaxies and clusters “due to their relative motions and lensing action” is not observed mass — it is inferred mass. The inferences made are based on standard assumptions about the behavior of light. These assumptions, formulated in flat spacetime, may not apply at astronomical scales of measurement — scales in which cosmic curvature would become a factor. If cosmic curvature induces unmodeled components of spectral shifts which systematically corrupt radial velocities, then it will be manifestly demonstrated in the data returned by ESA’s Gaia mission (2011 – 2016) and the astrodynamical evidence for CDM will suddenly be invalidated. The evidence of galactic lensing will also be in need of an alternate explanation.
Erik, I have no strong belief re CDM, either way it goes, I am only making my own non-specialist assessment of work on the subject. There is little doubt that there are some serious difficulties on both sides of the issue.
Regarding observations vs. inferences, I would point out that all observations are inferences to some degree. For example, energy loss in a pair of orbiting neutron stars matches GR’s predicted loss by gravitational radiation, yet we have not gotten a detection of such radiation from LIGO or other gravitational wave detectors. Whether we call Hulse and Taylor’s work an observation or an inference, the result is good. The same could be said for gravitational lensing, though with less confidence in the precision of the measurements, as you correctly point out.
On “direct” detection of CDM, our exchange and a recent entry in the Cosmic Variance blog reminded me of this assessment of one experiment that is controversial:
http://blogs.discovermagazine.com/cosmicvariance/2008/04/21/guest-post-juan-collar-on-dark-matter-detection/
There are references there to the papers, and the comments contain interesting points from some physicists.
Ron, the Hulse-Taylor object is, more precisely, a double-pulsar. I must admit here too that their orbital & mass parameters are not a matter of direct observation, but in this case I do not know of any physical mechanism that would louse up the timings of pulsar signals. So I do in fact believe that the component objects are indeed spiraling into each other in accordance with the predictions of G.R.
But I do not know that the ontological arguments for the existence gravitational-waves are sound. It seems to me that LIGO, manufactured at the cost of $365 Million, is merely a Super-sized replica of the Michelson-Morley experiment. Bigger price-tag — same results as 1887.
You might enjoy reading “Gravity’s Shadow” by Harry Collins — a tome so thick (~870 pages) that it exerts a gravitational field of its own. ;-) Collins discusses premature claims of gravitational-wave detection in the early 1970’s which perhaps entails parallels with the present quest for direct detection of CDM.
Erik, your choice of words imply you have some serious problems with the current state of physics. As in, pulsars possibly not being neutron stars, and the ontological reasons for gravitational waves. Not all neutron stars are pulsars, but there is exceptionally strong evidence that all pulsars are neutron stars. In the second case, ontology has nothing to do with it; gravitational radiation is a direct consequence of the field equations — you cannot have the field equations without gravitational radiation (ref. the Weyl tensor). That made Hulse and Taylor’s work Nobel-worthy, by confirming this extraordinary prediction of the field equations.
That LIGO has not yet made any confirmed detections is no surprise. The instrument is still evolving, and at its present sensitivity the probability of a detection is still very low. That will improve. Whether the money is well spent, I will not comment on since it isn’t being built with my tax dollars.
I have some familiarity with Joseph Weber’s work with aluminum cylinder detectors in the 70’s. They have since been shown to be ineffective due to (as I recall) quantum noise problems and their narrow bandwidth ~1 kHz. It was nevertheless an interesting attempt.
Atomic Dark Matter
Authors: David E. Kaplan, Gordan Z. Krnjaic, Keith R. Rehermann, Christopher M. Wells
(Submitted on 3 Sep 2009)
Abstract: We propose that dark matter is dominantly comprised of atomic bound states. We build a simple model and map the parameter space that results in the early universe formation of hydrogen-like dark atoms.
We find that atomic dark matter has interesting implications for cosmology as well as direct detection: Protohalo formation can be suppressed below $M_{proto} \sim 10^3 – 10^6 M_{\odot}$ for weak scale dark matter due to Ion-Radiation interactions in the dark sector.
Moreover, weak-scale dark atoms can accommodate hyperfine splittings of order $100 \kev$, consistent with the inelastic dark matter interpretation of the DAMA data while naturally evading direct detection bounds.
Comments: 17 pages, 3 figures
Subjects: High Energy Physics – Phenomenology (hep-ph)
Cite as: arXiv:0909.0753v1 [hep-ph]
Submission history
From: Keith Rehermann [view email]
[v1] Thu, 3 Sep 2009 21:29:30 GMT (187kb)
http://arxiv.org/abs/0909.0753
Ron… it would seem that I have failed to choose my words carefully enough, because I do understand that pulsars are neutron stars. My intention was to add precision to that part of the discussion.
I will defer my skepticism of LIGO until after its detectors are upgraded.
Cheers,
Precise Picture Of Early Universe Supports ‘Dark Matter’ Theory
A photograph of the QUaD telescope inside its groundshield taken from a crane above the telescope.
by Staff Writers
Cardiff, UK (SPX) Nov 03, 2009
A detailed picture of the seeds of structures in the universe has been unveiled by an international team co-led by a Cardiff University scientist. The team has obtained extremely precise data about the early universe, using a telescope near the South Pole in the Antarctic.
Their measurements of the cosmic microwave background – a faintly glowing relic of the hot, dense, young universe – provide further support for the standard cosmological model of the universe. The findings confirm the model’s prediction that dark matter and dark energy make up 95% of everything in existence, while ordinary matter makes up just 5%.
In a paper published in The Astrophysical Journal, researchers on the QUaD telescope project have released detailed maps of the cosmic microwave background (CMB).
Full article here:
http://www.spacedaily.com/reports/Precise_Picture_Of_Early_Universe_Supports_Dark_Matter_Theory_999.html
Dark matter is wrong idea. See: Boris V. Alexeev arXiv:1007.2800 “Solution of the Dark Matter Problem in the Frame of the Non-Local Physics”
But the situation is much more serious – the situation with dark matter reflects the total crash of the local Boltzmann kinetic theory. See: Boris V. Alexeev “Generalized Boltzmann Physical Kinetics” Elsevier, 2004. The generalized non-local kinetic theory will be delivered during my stay in USA in two months.