DARK AND STORMY: A variety of competing dark matter detectors are producing results at odds with one another. So far dark matter has been convincingly detected only by its gravitational effects. Here the inferred location of dark matter in galaxy cluster Abell 1689 is marked by a purple glow.
Image: NASA, ESA, E. Jullo (Jet Propulsion Laboratory), P. Natarajan (Yale University), and J.-P. Kneib (Laboratoire d'Astrophysique de Marseille, CNRS, France)
-
The Best Science Writing Online 2012
Showcasing more than fifty of the most provocative, original, and significant online essays from 2011, The Best Science Writing Online 2012 will change the way...
Read More »
BALTIMORE—The generic line on dark matter is that nobody really knows what it is because nobody has seen it. The former claim remains basically unassailable—there are many forms dark matter could take. But one research group would dispute the latter assertion. Over the past several years, the Italian DAMA (for DArk MAtter) collaboration has been making the claim that their subterranean detector has registered the signature of dark matter as Earth passes through a sea of the stuff. But despite an ever-strengthening observational case for their claim, the DAMA collaboration's finding remains a source of broad skepticism within the scientific community.
The situation was highlighted this week at a symposium on dark matter here at the Space Telescope Science Institute (STScI). A May 2 talk by a DAMA scientist was immediately followed by a presentation about a competing dark matter detector—one whose results are more widely accepted and whose data contradict DAMA's finding. A few days later a third scientist representing a third detector weighed in, and confused the situation even more.
Dark matter provides the universe with a great deal of its total mass, so it is critical to cosmic evolution, but it is both invisible and barely interactive with normal matter, making it an incredible challenge to detect directly. So far its existence has been inferred from its gravitational effects in shaping galaxies and other large-scale structures.
Pierluigi Belli of the University of Rome Tor Vergata and the DAMA collaboration explained that his team's detector has measured an annual fluctuation in particulate hits that seems to fit the bill for dark matter. DAMA is a detector meant to measure changes in the ambient particle environment—including, presumably, dark matter—as Earth passes through its orbit. "The velocity of Earth in the galactic frame is different at different times of the year," Belli explained. As the sun moves steadily through its orbit around the galaxy, Earth orbits the sun in turn, and the planet's velocity either adds to or subtracts from the sun's velocity. If dark matter rings the galaxy as theory predicts, Earth should be oscillating back and forth through a sea of particles. And DAMA should be able to register a yearlong ebb-and-flow cycle in the number of dark-matter particles passing through the detector.
The DAMA experiment consists of 250 kilograms of crystalline sodium iodide concealed deep underground in Italy's Gran Sasso National Laboratory. Burying the detector underground shields the instrument from more mundane particles, whereas dark matter should pass through rock and into the lab relatively easily. The hope is that some of those particles, having cruised cleanly through Earth, will then bump into one of the atoms in the DAMA detector, announcing its presence by depositing a tiny bit of energy in the crystal.
In more than a dozen years of operation, DAMA has registered a seasonal fluctuation in particle hits that agrees with what a dark matter sea should look like. As predicted, the fluctuation cycle peaks around the start of June and lasts almost exactly a year. "The results are well compatible with many dark matter scenarios," Belli said. Specifically, DAMA could be seeing a very lightweight form of the preferred candidate for dark matter, known as the weakly interacting massive particle, or WIMP. "We have positive evidence for the presence of dark matter particles at a very high confidence level," Belli said.
The general criteria for announcing evidence suggestive of a new particle or physical effect is three standard deviations, or 3 sigma; the benchmark for claiming a new discovery is 5 sigma. The DAMA seasonal flux is now a roughly 9-sigma effect. But doubts of the dark-matter interpretation still loom large.
"I think everyone would agree at this point that they see a signal," says STScI astronomer Mario Livio. "The question is: What is it?" Other researchers at the meeting echoed the same sentiment—after all, a 9-sigma result demands some explanation, even if it is not the dark-matter explanation the experimenters have offered. "It's an intriguing hint," Stanford University physicist Peter Graham said in an April 4 panel discussion at the symposium. "They clearly have a signal, and they've been seeing it for a long time."
Albert de Roeck, a physicist working at the Large Hadron Collider outside Geneva, Switzerland, suspects that DAMA scientists may have gotten off on the wrong foot with their peers. DAMA first announced evidence for a seasonal modulation indicative of dark matter more than 10 years ago, when the signal was much weaker than it is now. Not everyone was convinced. "It sort of seemed like they wanted it to be there," de Roeck says. Now, even with much stronger evidence, the field remains dubious.
Physicists have complained that the DAMA group has not been open enough with its data. During Belli's talk, physicist David Cline of the University of California, Los Angeles, noted that other researchers have not been given access to the raw, unprocessed data from DAMA to see how the collaboration arrived at their 9-sigma result. "It would be nice to get a look at that," Cline said. "Usually in science people do open their doors to let other people look at their data."
Belli said that that was simply not the procedure. "These data have been analyzed in the simple standard method," he said. "So we don't think that it's important to give the particular data."
The neighboring Xenon100 experiment has not helped DAMA's case. Xenon100, which is located in the same underground lab, works in a similar way to DAMA. Its detector, with a 62-kilogram liquid xenon target, has been awaiting collisions from dark matter since 2009. It boasts a very low level of background noise that should make it exquisitely sensitive to detecting ambient dark matter particles.
In a talk immediately following Belli's, Elena Aprile of Columbia University showed data from an April Xenon100 study that appeared to rule out the kind of lightweight dark matter particle favored by DAMA. What is more, the experiment did not pick up any kind of seasonally varying signal. In 100 days of taking data Xenon100 was unable to gather any evidence for the presence of dark matter, despite its sensitivity. "I didn't want to say it in words," Aprile said when asked to explain the discrepancy between her experiment and DAMA, "but…of course, already since some time, these data and others are in friction with that. They're not compatible."
Later, during the panel discussion, Belli was pressed to offer an explanation for what the DAMA signal might represent if it is someday proved not to be dark matter, as most observers suspect. "It is quite difficult to demonstrate that it's not dark matter," Belli said, adding that he and his colleagues have tried to exclude every other effect they can think of. "We cannot explain it in another way."
The last speaker of the symposium gave DAMA a glimmer of hope. Juan Collar of the University of Chicago, presenting May 5 on behalf of the CoGeNT (Coherent Germanium Neutrino Technology) experimental collaboration, announced that his group also registered a faint seasonal modulation in particulate hits. The CoGeNT dark matter detector had its experimental run cut short at 15 months due to a March fire in the Soudan Mine in Minnesota where it resides. But in analyzing that limited data Collar and his colleagues found a possible signature of seasonal modulation akin to what DAMA has seen.
CoGeNT's results are in broad agreement with a DAMA-like dark matter ebb and flow in terms of the timing, duration and amplitude of the seasonal variation. With a few basic assumptions, the CoGeNT signal becomes a 2.8-sigma result—not enough to make a strong statement, but enough to raise a few eyebrows. "We're not going to claim that we're seeing WIMPs," Collar cautioned.
He charged that the Xenon100 collaboration has overstepped in using its own nondetection to rule out the DAMA claim. "Xenon is not a good medium for light WIMPs," Collar said. "Light WIMPs are wicked.... With present technologies there's very little we can say [about them] with certainty." He had harsh words for a smaller, earlier iteration of the Xenon100 detector known as Xenon10. In one of the slides accompanying his talk, Collar referred to some results from Xenon10 as "pure, weapons-grade balonium."
CoGeNT may turn out to be the ally DAMA has long lacked—Belli, who tucked himself quietly in a back corner of the auditorium for most of the symposium, moved up to the third row for the CoGeNT talk. But Collar maintains he is not taking sides. "Maybe DAMA's wrong, maybe they're right, but we have to remain neutral," Collar said. "I find myself caught between the believers and heathens."
See what we're tweeting about
45 Comments
Add CommentIs there anyone out there with academic street cred willing to pose an obvious alternative? Namely, that 'dark matter' is dark because it isn't matter. Since matter and it's motion have, once again, been confirmed to mold space-time, is it not reasonable to hypothesize that so-called dark matter is a second order affect of groupings of matter, whose relativistic affects superimpose to warp space-time in a distinct manner at galactic scales? Is there any obvious reason why this option shouldn't share the stage with the "believers"?
Reply | Report Abuse | Link to this
Reply | Report Abuse | Link to thisIn my opinion astrophysicists have already observed the galactic dark matter objects - in fact, billions of them.
The MACHO microlensing results, and the 6x radio background excess seen in the ARCADE-2 experiment, are consistent with a huge population of "primordial" stellar-mass black holes.
Perhaps the evidence for dark matter has been in hand and staring us in the face for over a decade, but it has been ignored because it is the "wrong" answer, i.e., not the one the particle physicists desperately want.
Knee-jerk nay-sayers should informed that "primordial" black holes are fundamental objects that do not conflict with nucleosynthesis constraints.
Robert L. Oldershaw
http:/www3.amherst.edu/~rloldershaw
Discrete Scale Relativity; Fractal Cosmology
They are obviously measuring our velocity within the Ether.
Reply | Report Abuse | Link to this3 sigma is 99.73002039% (of a population), or
Reply | Report Abuse | Link to this2699.80 missed opportunities per million.
5 sigma is 99.99994267% (of a population), or
0.573 missed opportunities per million.
9 sigma (rounded to 30 decimal places is 100.000000000000000000000000000000%, or 0.000000000000000000000000000000 missed opportunities per million.
Could matter be 'dark' because it's time is slightly skewed from our own? Multiple universes should be able to birth elements and effects that we cannot measure or perceive.
Reply | Report Abuse | Link to thisAnybody who claims to know "for sure" what dark matter is, is delusional, self-aggrandizing, and severely lacking in humility. The jury is still out, and I suspect it will be out for a long time -- longer than anyone currently alive will get to appreciate. I will continue to be happy to entertain all the theories, but dark matter and dark energy seem fundamentally to demand some new science, new paradigms, and new instruments.
Reply | Report Abuse | Link to thisSo, you've posited a hypothesis with some corroborating evidence. That is useful. You're "knee jerk" rhetoric is not. In fact, relativistic lensing is also consistent with second order relativistic behavior. At first glance, I don't think 6x radio background is counter to my submission in this still open quest, but I'm intrigued and will look into it.
Reply | Report Abuse | Link to thisIf evidence is found for actual matter that is dark, then great; but until then, I recommend being open to all parsimonious hypotheses that account for the available evidence.
doesn't dark matter "disappear" if the gravitational constant isn't?
Reply | Report Abuse | Link to thisBoy oh boy David are you ever right! I hate the CRAP he (I assume it's a he) and his ilk pollute SA's site with. SA needs a spam filter like "The Economist" uses.
Reply | Report Abuse | Link to thisForgive a crazy conjecture, but if matter collapses space, why can't anti-matter source / expand space. As such, anti-matter would be responsible for what is called dark energy and dark matter.
Reply | Report Abuse | Link to thissee:
Reply | Report Abuse | Link to thishttp://www.benthamscience.com/open/toaaj/openaccess2.htm
Macho's and stellar mass black holes are just one part of the answer.
The other part of the answer lays in understanding that such black holes and the supermassive black hole at the centre of the galaxy exert an extra amount of gravity; 6.25 X the normal amount to be exact
I would like to comment vis-a-vis another discussion in SciAm pages last year [In praise of scientific error
Reply | Report Abuse | Link to thisBy George Musser | Dec 20, 2010 01:00 PM |]. Jim Dwyer = jtdwyer commented there that dark matter on the scale of spiral galaxies as inferred from spiral disk rotation curves is actually misguided inference. This has also been my view for many years now, starting end of 2005. I have written about this over the years [arXiv:0806.1131, arXiv:0805.4163, arXiv:0809.1972, arXiv:astro-ph/0703430]. Jim (jtdwyer) recently sent me a couple of corroborative papers [http://arxiv.org/abs/1007.3778, http://iopscience.iop.org/0004-637X/679/1/373/]. The bottom line from many independent individuals & groups around the world is: DISK GALAXY ROTATION CURVES ARE FULLY ADEQUATELY MODELLED USING NEWTONIAN DYNAMICS AND GRAVITY WITHOUT ANY NEED DARK MATTER. Jim has commented on this topic in several more (sometimes inapproriate) SciAm discussions as well.
b4 I start I think they got mad at me for comments intended towards the clown that keeps posting ads on the site. In the words of Gilly on Saturday Night Live 'Sorry'...
Reply | Report Abuse | Link to thisRegarding Jtdwyer he is on a mission to reject dark matter, dark energy and most of the 96% of the universe we cannot explain. His comments are interesting and thought out but I feel like he goes to Fox News only. I have read Green, Sussking, Hawking and Smolin (plus anything I can find on Smolin and Feynman). Smolin is on to something when I read his work on loop quantum gravity and he and Feynman together present some interesting concepts.
I like Mandelbrot's take on fractals and chaos and as I read QED I keep thinking that as we put more energy in the more interesting things come out but they are similiar to existing objects just at a higher energy level (Heavier). Maybe we are looking through the mirror the wrong way. Maybe the more massive objects are layers of a multidimensional universe where our view is directly related to our energy level.
By that I mean we are a mere 270 degrees Celsius from absolute zero. We are very close to the low end of energy and I am sure that affects our view of the whole picture.
Again sorry about the add crap but that guy needs to stop so how about pretty please?
I meant to include Freeman Dyson. He is one of the most important underrated physicist of our time and he is still with us. Thanks to Freeman the world can actually use quantum math. Plus he reads a lot like Einstein in his love of mankind.
Reply | Report Abuse | Link to thisThey have removed all of my post. I was playing with that guy that kept putting adds on the site all the time. Maybe it was the magazine putting up the adds to make some money. Well if this disappears I ll be back and I guess use a made up name like everyone else. Thanks for the thanks.
Reply | Report Abuse | Link to thisIs it possible that since the only thing that can be "detected" is the gravitational effect, that the source of the gravitational effect is actually located in one of the rolled up dimensions posited by string or M-Theory? It seems to me that just because a dimension may appear rolled up from our perspective does not mean that it can not have some effect of the other dimensions. Who knows, all the dimensions could be fully expanded at the same time but most only appear to be rolled up from our perspective.
Reply | Report Abuse | Link to thisI keep wondering why other dimensions are rolled up and not considered outside of our dimension. Where does it say that extra dimensions are microscopic vs macroscopic?
Reply | Report Abuse | Link to thisThanks for your comments. I am on a mission to expose the analytical errors that produced the perceived requirement for, especially, galactic dark matter. I am doing so strictly as a professional courtesy to the scientific community and the public. As I always strive to make clear, I'm a retired information systems analyst - it is that expertise that I can apply to these issues. I have no financial or professional interest in these matters.
Reply | Report Abuse | Link to thisFYI, I don't pay any attention to Fox News, only sciam.com and news.sciencemag.org. I read "Scientific American" and "Science News" for a couple of decades and I have been an AAAS member and subscribed to "Science" in the past. I have watched all the silly Science Channel and other video programs in the past couple of years. Most of my detailed information comes from related research archives.
Regarding books written by famous scientists, keep in mind that they may contain quite a bit of highly qualified personal opinion and conjecture, perhaps aligned with professional agendas, along with some fluff to interest a general readership. Unlike scientific journal articles, book publication does not require any adherence to formal peer review procedures.
The existence of dark matter is not in doubt.
Reply | Report Abuse | Link to thisAstronomers have know for decades that some kind
of invisible material is present around galaxies, because the velocities of stars do not fall off
with distance from the centers of the galaxies
as they should if mass were present in the visible
matter (gas, dust, and stars) only.
The question posed here is what is it, light "WIMPS,"
or something else.
You might want to read a few more Scientific American articles before you declare that the existence of dark matter has been proven. Please see:
Reply | Report Abuse | Link to this"Reliance on Indirect Evidence Fuels Dark Matter Doubts"
http://www.scientificamerican.com/article.cfm?id=dark-matter-doubts
"Tweak Gravity: What If There Is No Dark Matter?"
http://www.scientificamerican.com/article.cfm?id=dark-matter-modified-gravity
"What's The Matter?: Cold Dark Matter and the Milky Way's Missing Satellites"
http://www.scientificamerican.com/podcast/episode.cfm?id=A2B71EFB-ABFA-C6D7-0A728C56892215F8
By the way, Newton proved in his "Principia" that Kepler's equations describing planetary dynamics (only later called the 'laws' of Planetary Motion) presumed that the masses of orbital bodies were negligible in comparison to the mass they orbit and did not usually perturb each other's orbit.
Reply | Report Abuse | Link to thisThat is because Kepler's 'laws', illustrated by the rotational curve diminishing with distance from the axis of rotation, were directly derived from the observation of the planets in the Solar system, in which 99.86% of total mass is contained within the Sun.
In all cases, stars within the discs of spiral galaxies do not independently orbit any single central object of mass. Instead it is they that produce gravitationally bound substructures that rotate around a collective center of mass.
While it was earlier thought that stars in the discs of spiral galaxies orbit a central galactic bulge composed of billions of stars, it is now known that several large, well defined spiral galaxies do not even contain a central bulge.
So much has been concluded based on the presumptions that the dynamic motions of the disparate mass distributions of enormous galaxies should exactly match those of our comfortably familiar but so much simpler Solar system. They do not and can not. I hope we can soon stop wasting our time on such matters.
If our three (four) dimensional universe is pinned to a higher dimensional membrane, then we are also pinned to its topology. No dark matter needed.
Reply | Report Abuse | Link to thisIt's not quite that matter itself bends spacetime. It's the mass of the matter that warps it. Since antiparticles have the same mass as their 'normal' counterparts, they affect spacetime in the same way.
Reply | Report Abuse | Link to thisI find it odd that the Italians are not sharing data. Could this be because it is faked and they don't want to be caught in fraud as so many scientists have recently? I don't think fraud is likely but we can't exclude something just because it is distasteful.
Reply | Report Abuse | Link to thisI'm also curious as to just how they are qualifying the standard background activity that the Xenon100 specifically explained. If as they state, their test crystals are much more sensitive then perhaps they are getting more reaction from gamma particles and ambient non-dark matter. If there is a seasonal change then there is also the angle and distance from the sun that may account for this difference. It would be nice if they would stop being defensive and would actually engage in proper scientific procedure.
In the long run I think it likely that it will be established that the "dark matter/energy" explanation is incorrect for galactic scale activity. Something may be out there and the Italians may be the first to interact with matter in a form not controled or detected by humans before. Time will tell.
Very good point re. the seasonal variation of detection events - as I understand, that strongly indicates the Sun as the source of these mysterious detection events.
Reply | Report Abuse | Link to thisI very seriously doubt that they're detecting any dark matter necessary to account for observed galactic rotation characteristics, but they may be detecting some other, unidentified, phenomenon.
If the sun caused the seasonal variation, it would cause an even more pronounced daily fluctuation.
Reply | Report Abuse | Link to thisThat seems to be a very good point too, but if the detections are of some energetic particles emitted by the Sun that have passed through the Earth, there may not be any daily variation in detection rates.
Reply | Report Abuse | Link to thisThe researchers' suggestion seems to be that the Earth's orbit passes nearer to a halo of dark matter, increasing collisions with DM particles.
However, the galactic disk is known to be surrounded by a spheroid halo or corona of gas and dust that also contains old stars and globular clusters that, as I understand, do not exhibit any indications of the presence of dark matter. As I understand, any halo of dark matter must exist beyond this coronal halo of ordinary matter. In that case, I don't see how variability in Earth's orbit within the Solar system could possibly increase its necessarily weak interactions with any dark matter.
Perhaps the seasonal variation of Earth's orbit within the Solar system is increasing our interaction with the ordinary matter of the galactic coronal halo, increasing the energy of these sensitive crystal detectors. More likely, though, the crystals are interacting with some energetic particles emitted by the Sun...
The seasonal fluctuation is due to the variation of earth's velocity through the galaxy. For half of earth's orbit it is going in the same general direction as the sun, thus faster. The other half, slower, because it's going the opposite direction (generally) to the sun's proper motion. The variation of detected interactions is only proportional to the velocity of earth through the galaxy, not its proximity to anything. (Proximity may matter a lot, but is not described in this article.)
Reply | Report Abuse | Link to thisThe article's discussion of the cause for seasonal variation is unclear, especially it's initial discussion of velocity, but it goes on to state:
Reply | Report Abuse | Link to this"If dark matter rings the galaxy as theory predicts, Earth should be oscillating back and forth through a sea of particles. And DAMA should be able to register a yearlong ebb-and-flow cycle in the number of dark-matter particles passing through the detector."
It doesn't seem likely to me that Earth's relative velocity to the Sun within the galactic frame would be significant relative to the velocity of energetic particles that pass through the Earth.
In any case, the Earth's seasonal orbital variations effect its motions within the Sun's heliosphere - within the Sun's frame as it and its neighboring stellar masses rotate together through the galactic plane. I fail to see how the Earth's relatively trivial motion or velocity through the galactic plane could increase its interactions with a 'sea' of exceedingly weakly interactive dark matter that must lie beyond the galactic plane, beyond the galaxy's coronal halo of gas, dust, old stars and globular clusters.
I also don't think that the beating of my heart increases the exposure of its tissues to ambient X-rays as I walk through the airport.
"The researchers' suggestion seems to be that the Earth's orbit passes nearer to a halo of dark matter, increasing collisions with DM particles."
Reply | Report Abuse | Link to thisOh, and I thought it was something along the lines of the Michaelson-Morley experiment. I was probably mistaken, after all, I'm not an information analyst.
"The velocity of Earth in the galactic frame is different at different times of the year," Belli explained. As the sun moves steadily through its orbit around the galaxy, Earth orbits the sun in turn, and the planet's velocity either adds to or subtracts from the sun's velocity." Then he says, "Earth should be oscillating back and forth through a sea of particles." The term "back and forth", IMHO, does not convey the intent of the statement. He is talking about velocity relative to the preferred frame of rest of the galaxy and the purported cloud of dark matter.
Reply | Report Abuse | Link to thisThe Sun's velocity is 371 km/s and Earth's is 29 km/s. In early June, Earth moves at 400 km/s relative to the frame of rest. In early December, 342 km/s (about 85%.) Compare the rate of bug/windshield impacts at 60 mph vs. 51 mph. Easily measurable.
These velocities are negligible to those of neutrinos and cosmic rays, which travel at relativistic speeds, up to light speed. WIMPs, on the other hand, are more akin to clouds of massive particles at orbital velocities. (I don't mean to imply that I know anything about WIMPs or their behavior or even if they exist: I'm just trying to frame the description of the article as I see it.)
The locations of these clouds is not excluded from the plane of the galaxy nor from the center. They and the normal matter coexist. Picture the distribution of dark matter like that of an elliptical galaxy sharing the center of mass of the visible galaxy. Exceptions exist, such as the Bullet cluster in which the dynamics of galactic collisons has displaced the visible matter.
I should have said, "Picture the distribution of dark matter like that of an elliptical galaxy sharing the center of mass of the visible isolated galaxy, or the center of mass of a visible galactic cluster."
Reply | Report Abuse | Link to thisI'll defer to your superior knowledge of GR, but it seems very difficult to misunderstand the meaning of "Earth should be oscillating back and forth through a sea of particles." However, that issue may not really be important...
Reply | Report Abuse | Link to thisI think the principal issue here is that particle physicists are working on the basis that dark matter permeates the galaxy. However, the gravitational requirement for galactic dark matter is to provide peripheral galactic mass to account for the flat or often increasing, rather than diminishing, rotational velocity of ordinary matter. As I understand, the more mass that is included within the inner radius of the galaxy the greater the expected velocity of stars within the galactic disk. The distribution of dark matter is critical to its ability to explain galactic rotation.
While not a definitive reference, wikipedia specified that the Milky Way's dark matter halo "covers the space between 100,000 light-years to 300,000 light-years from the galactic center." I think this is generally consistent with the constraints planed on dark matter by astrophysicists thus its descriptive name 'halo' rather than 'cloud'. Please see:
http://en.wikipedia.org/wiki/Dark_matter_halo#Milky_Way_dark_matter_halo
There seems to be some fundamental discrepancies here...
Agreed: there seem to be some fundamental discrepancies here...
Reply | Report Abuse | Link to this"A dark matter halo is a hypothetical component of a galaxy, which extends beyond the edge of the visible galaxy and dominates the total mass."
http://en.wikipedia.org/wiki/Dark_matter_halo
"The Galactic Center is a particularly good place to look as it contains the largest dark matter abundance."
http://en.wikipedia.org/wiki/Dark_matter#Composition
I don't know if those two statements are really contradictory. As you state, the dark matter is in the halo. I thought of the halo as the outer portion (beyond the extent of the visible galaxy) of the dark matter. Most of the mass is in the outer half-radius. If it's evenly distributed the inner half-radius would contain only 1/8th of the total.
Either way, the lateral wobble of earth's path through the galaxy is only 15 light-minutes. Unless there's a fine grain structure to the dark matter, that wouldn't change the proximity by much compared to 100's of 1000's of light-years. Thanks for the link. I want the answers and I want them soon...not gettin' any younger here! Hopefully we're not just talking past each other.
That's great! I think wikipedia entries are produced by whoever shows up and some subject area moderators, but I suspect this does illustrate a real discontinuity between the two (or more) subgroups of physicists.
Reply | Report Abuse | Link to thisI may be ignorant but I know what cow pies smell like, having stepped into so many myself! Hopefully, eventually, someone more capable can clean this stuff up...
That's great! I think wikipedia entries are produced by whoever shows up and some subject area moderators, but I suspect this does illustrate a real discontinuity between the two (or more) subgroups of physicists.
Reply | Report Abuse | Link to thisI may be ignorant but I know what cow pies smell like, having stepped into so many myself! Hopefully, eventually, someone more capable can clean this stuff up...
By the way, the wiki section I referenced also states:
Reply | Report Abuse | Link to this"The dark matter halo is the location of nearly all of the Galaxy's dark matter, which is more than ten times as much mass as all of the visible stars, gas, and dust in the rest of the Galaxy."
I really don't do math, but I think that 1/8 * 10x means that dark matter within the visible galaxy would nearly double the mass within the region of observable rotational velocities. In that case, it'd seem that doubling localized mass would also effect the evaluation of planetary motions as well...
The materials used in the "dark matter" detectors are different. The suggested regularity or seasonality of one and possibly of another that failed early due to fire damage is not conclusive. We know that matter comes in two basic forms. One is the permanent form of which we and what we see/& commonly detect are made of. The other form is virtual particles. These cannot be detected but must exist via particle or quantum physics theory.
Reply | Report Abuse | Link to thisWhat we might be seeing is a third, yet perhaps a now detected but still unidentified form of matter, mid-existent matter. It might last long enough for some detectors to notice but not so for others. If mid-existent particles exist then it might act to make up some of the dark matter mystery. If so ... we are looking at new physics. It's an exciting possibility, full of new connections! I plan to publish my theory of everything later this year.
"There seems to be some fundamental discrepancies here..."
Reply | Report Abuse | Link to thisNo particular discrepancy. First, the authors of that article may not be the best at explaining, secondly, they may not really understand what they're talking about. Wikipedia is written by any teenager who comes along and feels like it and moderated by any other unemployed dude who has nothing better to do. In some cases this may turn out just fine, particularly for simple straightforward and well established stuff, the details of which is in no doubt. Want to know when Nixon was president? Check Wikipedia, it will probably be right (with emphasis on "probably!")
There are many procedures in place in Wikipedia intended to improve the quality of the entries, and it's really quite surprising how much good information you can find there, but there's still a lot of substandard material, and if you're confused, there is at least a chance that it's because the Wiki editor was equally confused.
What students who have entered university after Wikipedia was created, have been told most of all during initial classes is, Wikipedia is NOT a reference. DON'T trust the information in Wikipedia! And DON'T refer to Wikipedia as a source in your work!
The moderate version is, only use Wikipedia as a source for peripheral information without much significance for your argument.
Obviously the dark matter must be present within the outer radius of the visible matter. Not only have I never heard any suggestion that there should be a mechanism for expelling it from the inner regions of galaxies (there may be, I just haven't heard of it), but more importantly if it was present only in a hollow halo on the "outside" it would have no or (in the case of a distribution with nonspherical symmetry) extremely little effect on the observed velocity curves.
Even if present in great amounts in the inner regions of the galaxies, it will have virtually no effect on the orbits of planets in the Solar system. They're much too close to each other and the Solar system as a whole represents an area of immensely high average density compared with the surrounding volumes of space, whether there be dark matter or not. And even if it was present in significant amounts between planets, it wouldn't have much effect unless it was unevenly distributed on the very small scale of the Solar system. That seems unlikely.
Using the word "oscillations" may have been ill advised. The orbit of the Earth around the Sun is of course a form of oscillation, but that description appears to have caused confusion.
Here is the article cited by the wikipedia 'peripheral halo' refernece, published 12/2005, Monthly Notices of the Royal Astronomical Society, Volume 364, Issue 2, pp. 433-442:
Reply | Report Abuse | Link to thisBattaglia et al (2005), "The radial velocity dispersion profile of the Galactic halo: constraining the density profile of the dark halo of the Milky Way",
http://www.adsabs.harvard.edu/abs/2005MNRAS.364..433B
If you had referred to the referenced wikipedia entry you could have found the citation above yourself. Unfortunately, you casually dismissed it and proceeded to lecture me about wikipedia. Please do not lecture me. I am not a student - specifically, I am not your student.
If dark matter must be largely excluded from the region of the ordinary galactic matter in order to produce the observed rotational velocity characteristics, as I assert, then I agree there is no specified mechanism or characteristic property of fundamental particles that can account for it. In this case, I suggest that dark matter should be excluded as the probable cause for the discrepancy between observed galactic rotational characteristics and those predicted by standard galactic gravitational evaluation procedures - even if it is detected in some locations in some indeterminable quantity.
The solution should be easily understood by real scientists, particularly ones who a not locked into false assumptions.
Reply | Report Abuse | Link to thisNewton's law of gravity is based upon observations of planets in our solar system. In order for it to be a universal law of gravity it must also be supported by observations at cosmic distances. However, observations of the motion of groups of galaxies by Fritz Zwicky and of the flat (constant) rotation velocities of stars in spiral galaxies by Vera Rubin could not be explained by Newton's law and gravitational constant. A massive fudge factor of dark matter was introduced to supply the missing gravity and much scientific effort was wasted in attempts to find the supposed dark matter.
Actually, the solution resides in the equation balancing the gravitational force and the centrifugal force of rotation - which is M*G=r*v*v - and for the observed constant velocities in spiral galaxies, reduces to M*G as a linear function of distance r. The usual and serious error is to assign the linear dependence to the mass M, rather than to G, the already invisible gravity. Thus the true universal gravitational constant is G= G(newton) + A*r.
For details, see "The Misunderstood Universe". You will also learn the truth about Dark Energy.
It is time for scientists to work on real problems rather than on fudge factors.
Please see my earlier comment explaining that Vera Rubin inappropriately expected the laws of planetary motion to apply to discrete stars within the self-gravitating discs of spiral galaxies. This misconception established the perceived requirement for galactic dark matter. To analytically explain the rotational characteristics of galaxies without invoking invisible mass or modified gravity…
Reply | Report Abuse | Link to thisIn the early 21st century a retired aeronautical engineer, Kenneth Nicholson, produced a series of unpublished papers identifying errors in the original gravitational analyses that had established the general acceptance of the galaxy rotation problem in the 1970s. He also developed more appropriate methods of galactic gravitational evaluation using Newtonian dynamics and his universal law of gravitation. These papers received little attention for several years. These methods have been evaluated They can all be found listed in the references of: Nicholson, (2003,2007), "Galactic mass distribution without dark matter or modified Newtonian mechanics",
http://arxiv.org/abs/astro-ph/0309762
and: Banhatti, (2008), "Newtonian mechanics & gravity fully model disk galaxy rotation curves without dark matter",
http://arxiv.org/abs/0806.1131
(continued...)
(...continued)
Reply | Report Abuse | Link to thisMore recently, the earlier works of Kenneth Nicholson have been extended by physicists working in the field of materials research: Feng & Gallo, (2010), "Rotating thin-disk galaxies through the eyes of Newton",
http://www.arxiv.org/abs/1007.3778
A specific case using independently developed methods of representing thin discs has been published in the Astrophysics Journal: Jalocha et al, (2006-2008), "Is dark matter present in NGC4736? An iterative spectral method for finding mass distribution in spiral galaxies”,
http://arxiv.org/abs/astro-ph/0611113
These studies indicate that dark matter is not necessary to hold galaxies together: the gravitational effects of distributed masses is sufficient to prevent peripheral stars from being expelled by ‘excessive’ rotational velocity.
Employing galactic disc objects as microlenses have been used to test for the local presence of a dark matter halo: Sikora et al, (2011), "Gravitational microlensing as a test of a finite-width disk model of the Galaxy",
http://www.arxiv.org/abs/1103.5056
A study of hundreds of discrete Milky Way (ordinary matter) halo objects, including satellite galaxies, globular clusters, and old stars are used to constrain the mass and distribution of any possible dark matter halo:
http://www.adsabs.harvard.edu/abs/2005MNRAS.364..433B
More interestingly, unlike the (self-gravitating) galactic disc, these more distant discrete objects do generally comply with the Keplerian rotational curve! From that direct evidence I infer that it is the independent orbits of discrete objects around a dominating mass that produces orbital velocities diminishing with distance. Distributed mass galaxies should not be required to rotate like sparse planetary systems.
Since the theory of relativity has been declared to be wrong (see: Scientific American March 2009 or my IEEE paper on the absence of the time dilation at 33GHz) dark matter is not meaning much it belongs into the science fiction scene. That a couple of kilogramms of my body should consist of dark stuff (is it my soul?) is a good joke or swindle(words used by L.Essen for relativity theory). Or maybe they have observed (measured) dark energy another funny stuff. I am sure CERN scientists will soon find these black magic particles in the Large Hadron Collider and we taxpayers pay them.
Reply | Report Abuse | Link to thisIf you had taken a look at the article you yourself link to, you might have noticed that the plots consistently indicate a density decrease with distance from the center.
Reply | Report Abuse | Link to thisIn other words the halo is at least as dense in the central parts of the galaxy as it is anywhere else, and the dark matter is not excluded from the galactic disk. At least according to that paper. Maybe the Wikipedia article was badly written, maybe you misunderstood it, I don't know. I didn't check. I assumed that by halo they meant what is usually meant in astrophysics, and it turns out they did.
But maybe you just read a few paragraphs and assumed you understood the abstract, though you couldn't understand the math. Or in this case the graphs.
If you ever decide to really offer your professional services to the scientific community, rather than just writing about it on this popular science forum. I suggest you really do let yourself be lectured a little first. It's always a good idea when entering a new field, no matter how much experience you may have in other areas. (And I mean real lectures, not internet forum replies.)