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Research News at Vanderbilt

New, simple theory may explain mysterious dark matter

by | Posted on Monday, Jun. 10, 2013 — 3:50 PM

Abell 520 galaxy cluster

Abell 520 is a gigantic merger of galaxy clusters located 2.4 billion light years away. It appears to have left behind a large clump of dark matter. (Space Telescope Science Institute)

Most of the matter in the universe may be made out of particles that possess an unusual, donut-shaped electromagnetic field called an anapole.

This proposal, which endows dark matter particles with a rare form of electromagnetism, has been strengthened by a detailed analysis performed by a pair of theoretical physicists at Vanderbilt University: Professor Robert Scherrer and post-doctoral fellow Chiu Man Ho. An article about the research was published online last month by the journal Physics Letters B.

“There are a great many different theories about the nature of dark matter. What I like about this theory is its simplicity, uniqueness and the fact that it can be tested,” said Scherrer.

Elusive particle

Scherrer and Ho

Robert Scherrer, left, and Chiu Man Ho. (Joe Howell / Vanderbilt)

In the article, titled “Anapole Dark Matter,” the physicists propose that dark matter, an invisible form of matter that makes up 85 percent of the all the matter in the universe, may be made out of a type of basic particle called the Majorana fermion. The particle’s existence was predicted in the 1930’s but has stubbornly resisted detection.

A number of physicists have suggested that dark matter is made from Majorana particles, but Scherrer and Ho have performed detailed calculations that demonstrate that these particles are uniquely suited to possess a rare, donut-shaped type of electromagnetic field called an anapole. This field gives them properties that differ from those of particles that possess the more common fields possessing two poles (north and south, positive and negative) and explains why they are so difficult to detect.

Common electromagnetism, not exotic forces

“Most models for dark matter assume that it interacts through exotic forces that we do not encounter in everyday life. Anapole dark matter makes use of ordinary electromagnetism that you learned about in school – the same force that makes magnets stick to your refrigerator or makes a balloon rubbed on your hair stick to the ceiling,” said Scherrer. “Further, the model makes very specific predictions about the rate at which it should show up in the vast dark matter detectors that are buried underground all over the world. These predictions show that soon the existence of anapole dark matter should either be discovered or ruled out by these experiments.”

Fermions are particles like the electron and quark, which are the building blocks of matter. Their existence was predicted by Paul Dirac in 1928. Ten years later, shortly before he disappeared mysteriously at sea, Italian physicist Ettore Majorana produced a variation of Dirac’s formulation that predicts the existence of an electrically neutral fermion. Since then, physicists have been searching for Majorana fermions. The primary candidate has been the neutrino, but scientists have been unable to determine the basic nature of this elusive particle.

Invisible to telescopes

The existence of dark matter was also first proposed in the 1930’s to explain discrepancies in the rotational rate of galactic clusters. Subsequently, astronomers have discovered that the rate that stars rotate around individual galaxies is similarly out of sync. Detailed observations have shown that stars far from the center of galaxies are moving at much higher velocities than can be explained by the amount of visible matter that the galaxies contain. Assuming that they contain a large amount of invisible “dark” matter is the most straightforward way to explain these discrepancies.

Dark Matter - color corrected

Comparison of an anapole field with common electric and magnetic dipoles. The anapole field, top, is generated by a toroidal electrical current. As a result, the field is confined within the torus, instead of spreading out like the fields generated by conventional electric and magnetic dipoles. (Michael Smeltzer / Vanderbilt)

Scientists hypothesize that dark matter cannot be seen in telescopes because it does not interact very strongly with light and other electromagnetic radiation. In fact, astronomical observations have basically ruled out the possibility that dark matter particles carry electrical charges.

More recently, though, several physicists have examined dark matter particles that don’t carry electrical charges, but have electric or magnetic dipoles. The only problem is that even these more complicated models are ruled out for Majorana particles. That is one of the reasons that Ho and Scherrer took a closer look at dark matter with an anapole magnetic moment.

“Although Majorana fermions are electrically neutral, fundamental symmetries of nature forbid them from acquiring any electromagnetic properties except the anapole,” Ho said.

The existence of a magnetic anapole was predicted by the Soviet physicist Yakov Zel’dovich in 1958. Since then it has been observed in the magnetic structure of the nuclei of cesium-133 and ytterbium-174 atoms.

Particles with familiar electrical and magnetic dipoles, interact with electromagnetic fields even when they are stationary. Particles with anapole fields don’t. They must be moving before they interact and the faster they move the stronger the interaction. As a result, anapole particles would have been have been much more interactive during the early days of the universe and would have become less and less interactive as the universe expanded and cooled.

The anapole dark matter particles suggested by Ho and Scherrer would annihilate in the early universe just like other proposed dark matter particles, and the left-over particles from the process would form the dark matter we see today. But because dark matter is moving so much more slowly at the present day, and because the anapole interaction depends on how fast it moves, these particles would have escaped detection so far, but only just barely.

The research was funded in part by Department of Energy grant DE-FG05-85ER40226.

David Salisbury, (615) 322-NEWS

  • Fe02Dream

    I wonder- what impact does this theory have on the “expanding or collapsing universe” debate?

    • Jonny O

      Yes, it’s interesting. Previously, the accelerated expansion of the universe was thought to be caused by dark matter, but if dark matter is “slowing down” as the article suggests, the expansion rate logically should be as well.

      • LeickR

        Sorry, but you’re conflating dark matter and dark energy.
        Dark energy is theorized to be driving the accelerated expansion of the universe, not dark matter.
        Dark matter, on the other hand, would be expected to “cool”, or “slow down”, as the universe expands, just like ordinary matter.

      • Rebbman72

        Since they have gotten to absolute zero, and into negative K, it is possible that might exist In the dark matter? Further is it possible absolute darkness also exists ? Since time is essentially measured by the speed of light ( though photons may move faster than that? ) wouldn’t dark matter be without time? Or the “now?” That being a possibility wouldn’t we live in the “not now?”
        Supposedly it is never less that 2.7 K , but that notion is not the case anymore, if we can produce it in a lab here, would exist elsewhere?

  • Steve McAbee

    Magnetic forces seem to be becoming the key. I expect that unlocking the the secrets of electromagnetism will show us the way to inter-stellar travel.

    • buffonelder101

      how do you get magnetic forces without moving charge?

  • Adam

    Thank you for the (article) Mr. Salisbury.

  • Kenith Adams

    If most of the universe is comprised of dark matter doesn’t that make our electro magnetic fields the rare ones and not vice versa as the article states?

    • Mystgreen

      Agreed. Something that makes up 85% of the universe isn’t “rare”.

      • Jacob

        I’ve read mixed reports on that, I’ve also seen it represented as 23%, much more frequently in fact. 85% may just be downright wrong.

  • Chris Stinnett

    We amateur astronomers will doubtless be thrilled by this model, yet I’m still a little puzzled. Let me see if I can get this straight: undetectable particles of pretend matter that can’t be measured even though it is thought to make up 85% of the universe may actually be composed of magnetically theorized, but never discovered, matter that has been “examined” by scientists in their imaginations fueled by speculative computer models that may or may not accurately describe something that may or may not exist but that is currently held responsible for things we can’t understand.
    OK, at least it’s science and not, say, magic or alchemy. Or, God forbid, religious faith.

    • Carlos

      “Let me see if I can get this straight: an unseen force binds particles together via their mass, and its magnitude is proportional to the inverse square of their distance. Calculations using speculative computational models can possibly predict the trajectories of objects for all time based solely on the initial conditions? The models can someday be used to possibly send unmanned probes to the ends of the solar system?”

      Some guy before Galileo, Kepler and Newton…

    • martykayzee

      You candidly and concisely express your ignorance. How refreshing.

  • buffonelder101

    i thought this was already science fact /sarcasm

  • buffonelder101

    why don’t they just call this a magnetic monopole?… oh wait then they would have to eat all the bs they have been spewing for years…. get back to the aether people… you have washed away in a sea of relativity and have lost all objectivity

    • Pete

      I’m sure you have some solid mathematics to disprove General Relativity and to explain the observations made in Quantum Physics.

    • Dustin Ddraig

      Probably because it’s not a monopole. A normal magnet (dipole) has two poles, a monopole has one pole, and an anapole has zero poles (i.e., zero that can interact with other magnets). Calling it a monopole is just wrong.

  • Peter Parker

    This sounds really fascinating! I wish the article would have elaborated on what other predictions (practical or impractical) can be made if dark matter are indeed anapole particles.

  • fire115

    The effects of dark matter have been reproduced in lab enviorment in an unrelated experiment, yet no one is looking into it.

    GOOGLE this: Quantum gas goes below absolute zero

    “For instance, Rosch and his colleagues have calculated that whereas clouds of atoms would normally be pulled downwards by gravity, if part of the cloud is at a negative absolute temperature, some atoms will move upwards, apparently defying gravity4.

    Another peculiarity of the sub-absolute-zero gas is that it mimics ‘dark energy’, the mysterious force that pushes the Universe to expand at an ever-faster rate against the inward pull of gravity. Schneider notes that the attractive atoms in the gas produced by the team also want to collapse inwards, but do not because the negative absolute temperature stabilises them. “It’s interesting that this weird feature pops up in the Universe and also in the lab,” he says. “This may be something that cosmologists should look at more closely.””

    …and surprise surprise the universe is very cold place, i wonder how long it will take for sientists to acatualy talk to each other about this theory on dark matter.

  • Mark

    The part I find most disturbing is, ‘Detailed observations have shown that stars far from the center of galaxies are moving at much higher velocities than can be explained by the amount of visible matter that the galaxies contain. Assuming that they contain a large amount of invisible “dark” matter is the most straightforward way to explain these discrepancies.’ So, what the article says is because astronomers and physicists can’t explain what they are observing based on what they know, they decide that there is matter they can’t observe or describe which is affecting this movement. Sounds plausible, until you discover that the amount of matter needed to make their hypothesis correct is 5 times what they can see and it has a neutral electric charge! And they say that science doesn’t require faith! Hilarious!

    • martykayzee

      Faith rejects evidence. Science requires it.

      • alec o shea

        Evolution is a theory it has never been proven but is taught as if it is fact

  • Rick Shinholt

    If dark matter is invisible to the telescope but is there.. Then you would think that we should be running into dark matter all the time. since we are running into dark matter all the time then, it must be all around us. Just like flatland we are not able to see from our angle. I think it dimensional. I think it may be a time thing really. Just like radio waves we can use different frequencies to transmit multiple audio steams then maybe time has a multiple frequencies and there is different time lines. Think about it multiple time lines even on this earth. I think you can see this when quark travel at maybe faster then time and disappear (Different time line maybe) when atom are smashed together. Of course i could just be talk out of my…

    • Zaoldyeck

      Dark matter is a lot weirder than you seem to think, however the ‘flatland’ reference scares me a bit, because ‘what the bleep do we know’ massacred a lot of physics.

      First, dark matter actually does constitute more of the universe than we do, ‘matter’ only has roughly 5% of the energy density of the universe, while ‘dark matter’ has roughly 20%. (The vast majority is in ‘dark energy’, which is the ‘cosmological constant’ in our models, and that’s about all we really know so far about dark energy.)

      The reason it is ‘invisible’ is because it doesn’t interact with the electromagnetic spectrum. So since most astronomical research is conducted using light, be it infrared, visible, x-ray, etc, you can’t see something that doesn’t interact with light.

      You CAN however see the effects of dark matter. We see it in galactic rotation curves. Consider you’d expect a galaxy acting like a solar system, with a large center of mass and bodies rotating around it. Well look at Pluto, according to newtonian mechanics you’d expect the planets far away to have much longer orbits.

      But that doesn’t happen on galactic scales. Instead the rotation speed stays constant! The only way we can really explain this is if there’s a lot more mass, but it’s roughly evenly distributed throughout the galaxy.

      We also have some models for possible creation of dark matter, hints coming from the excess signal in the Higgs diphoton channel, but that’s another story entirely.

      PS, quarks can’t travel “faster than time”, time’s a dimension, you can’t travel “faster than space”. The relevant idea is travelling faster than light, but in general, no massive object (of which quarks qualify) can be accelerated to the speed of light. Coherent and demonstrated ‘warp’ models are still quite a ways away. Although it’d be nice if we spent more money researching new challenging scientific ventures.

  • Chris Stinnett

    Hey, Pete.
    No evidence? Really? The greatest minds of the past 2,000 years have focused their towering intellects upon Christianity. Some you might not be familiar with (Anselm, Aquinas, Alvin Plantinga, John Warwick Montgomery); others you’d recognize but never suspect them to be believers (Newton, Pasteur, Priestly). All of science is founded in a confident expectation that the universe is governed by rules that are understandable and explainable. It’s no coincidence that science flourished where Christianity laid a foundation of reason, thought, and a belief in a consistent Creator. I seriously doubt that you have the slightest inkling of the overwhelming scholarship devoted to the intellectual underpinnings of Christianity–and I seriously doubt that you will bother to investigate it. One thing I ask of you: please do not presume that because you don’t know something that means that nobody knows. Real scientists know that ignorance is not evidence of anything except ignorance.

    • Carlos

      Perhaps we could ask the likes of Galileo whether Christianity laid the foundations for his brand of independent scientific thought.

  • martykayzee

    If they comprise 85% of the matter in the universe, how are they rare or unusual?

  • fire115

    You seem to miss the point that neither Dark Energy or Dark Matter were never definitively defined and could be interrelated if not the same thing.

    From nassa:

    “More is unknown than is known. We know how much dark energy there is because we know how it affects the Universe’s expansion. Other than that, it is a complete mystery. But it is an important mystery. It turns out that roughly 68% of the Universe is dark energy. Dark matter makes up about 27%….
    Another explanation for dark energy is that it is a new kind of dynamical energy fluid or field, something that fills all of space but something whose effect on the expansion of the Universe is the opposite of that of matter and normal energy. Some theorists have named this “quintessence,” after the fifth element of the Greek philosophers. But, if quintessence is the answer, we still don’t know what it is like, what it interacts with, or why it exists. So the
    mystery continues. ”

    Translation they have no clue and it seem to me from everything i have read on the news updates on this subject matter, no detector, lab, experiment or satilite ever had been able to detect even one of them or anything that would even point to either, everything and everybody thus far failed to show what they or it really is. Clearly we are looking it from the wrong prespective would it not make sence to investigate the first and the only experiment that can actually explain the physics of universe expansion. To simply say “So you’re looking at 2 different things.” and throw out one of the only physical clues in decades is ignorant.

  • Andy Puckett, PhD

    As a Vanderbilt alumnus in physics, I respectfully submit that your diagram of the anapole magnetic field seems backwards. You may have your colors – and therefore your electric/magnetic fields – swapped. In the scientific paper by the authors, they say, “It is related to the toroidal dipole moment, which corresponds to a solenoid with the ends joined into a torus, producing an azimuthal magnetic field”. That suggests to me that your blue lines should be electric fields (and therefore be changed to red to match the bottom two parts of the diagram), and your red lines should be magnetic fields (and should change to blue). As drawn, your “anapole” case looks too much like the magnetic field of a short but ordinary solenoid, i.e., an electromagnet.

    • David Salisbury

      Thanks for pointing out the inconsistency. We have corrected it.

  • Edohiguma

    Donut-shaped? Does this mean The Simpsons were right all along?!

  • Dwight Carrell

    Metallic hydrogen.

  • Dwight Carrell

    Ultra-stable solid metallic hydrogen.

  • Walt Ballard

    Regardless of what kind of particles “Dark Matter” is made of, I propose the because it makes up 85% of the universe, that it is something that we fail to see because it’s right in front of our faces. Albert Einstein was the first to propose the substance. He called it SPACE/TIME! It is so common that we look through it just as a fish looks through water and we look through air.

    I’ll even go a step further, and propose that ALL matter is made up of “SPACE/TIME” simply knotted up and concentrated into clumps making up the various sub-atomic particles that make up the neutrons and electrons of atoms, that make up the molecules that in turn great all objects of mass.

    This would also apply to the missing “Dark Energy” for all particles, regardless of size, contain energy. It’s what eventually draws them together into clumps of matter, OR conversely “replies” matter from each other.

    I’ll confess, I’m not a trained scientist, and I’m not seeking recognition for this idea. I’ve watched a LOT of science shows discussing this topic and seeing the evidence presented with a less cluttered perspective presents me with this simple and straightforward solution. It seems like the ONLY logical answer to why 85% percent of the universe’s mass is dark, seemingly undetectable.

    ANYONE that finds this theory at all intriguing, PLEASE feel free to pursue it as your own if you would like. A footnote might be nice, but I am not looking for recognition. I just want someone to seriously investigate or pursue this proposal. Something inside me is eating at me, SCREAMING, “This is VITALLY important to our advancement in astrophysics! I believe that it will revolutionize our perception of the universe and our understanding of it. Perhaps even open the door to interstellar space travel someday. I also suspect it might alter our understanding of the “speed of light”.

    Think about it. It has been proven that light is affected by mass. Mass can bend light. A great enough mass can even stop, and reverse the direction of light! (Black Holes) So, why couldn’t light be slowed down as it passes through regions with high concentrations of “Space/Time”, aka, mass and energy. Then, inversely speed up as it passes through “LOW” densities of “Space/Time” (The gaps between galaxies.)

    Just, think about it.
    Thank you for indulging my tirade.
    This has been gnawing at me for years now, and I’ve been searching for some place I could present it that someone with the expertise to follow up on it might see it.

    • Archangel

      “…I’ll confess, I’m not a trained scientist…”
      Completely unnecessary to say that

  • Archangel

    “…and the left-over particles from the process would form the dark matter we see today …”

    I think he means “that we DON’T see today”

  • Armin Dick

    my thought of it is,
    baryonic matter may degrade to or very slowly transform into black matter (testable prediction, baryonic matter should get less with time as it transforms). Black matter was there before the Big Bang (that we are a part of), and may have been a cause of it. The black matter present in the span of our observable universe is partly from baryonic matter that has transformed back into it (since 14 billion yrs), and partly that was already there before the Big Bang.