A small step toward dark matter

By Phil Plait | October 21, 2008 12:30 pm

Dark matter — the mysterious stuff that doesn’t emit light, and doesn’t appear to interact with normal matter much if at all — outmasses normal matter in the Universe by a comfortable amount. We know it’s out there, and we even have a decent grasp of what it’s doing, but, maddeningly, we don’t know what it is.

We know what it isn’t. It isn’t cold gas, or dead stars, or rogue planets (seriously), or mini black holes. There’s a long list of things it might be, and most of those items have been checked off. All that’s left are weird particles that are only theoretical. We think they might exist, but our particle detectors and accelerators haven’t turned them up yet.

People are trying, though! In the LHC there is a special detector set up to look for dark matter. There are also other detectors spread out around the world looking for some sort of interaction of dark matter with normal matter.

Update: in this next paragraph, I originally had mistaken the Picasso group doing this work with the entire Observatory; I was corrected in the comments so I have fixed this paragraph.

One such detector is in Canada. Or, rather, below it. The Sudbury Neutrino Observatory is an astronomical observatory located over a mile underneath the Canadian landscape. Shielded by solid rock, detectors there are designed to look at subatomic particles from space such as neutrinos, ghostly particles created during some particle interactions. In fact, a detector at SNO was crucial in solving the Solar Neutrino Mystery.

Now it turns out they may help solve the dark matter mystery as well! Basically, the Picasso group at SNO is trying to detect one kind of proposed dark matter particle (a weakly interacting massive particle, or WIMP). The problem is, the signal from such a particle looks a whole lot like the signal they get from an everyday alpha particle — the nucleus of a helium atom, which is a common radioactive decay product. Differentiating between the two is really, really hard.

However, scientists with Picasso now think they’ve figured out a way to distinguish them:

“When we looked at our calibration data taken with neutrons and compared them with our alpha background data we saw a peculiar difference which we attributed first to some detector instabilities or gain drifts in our electronics,” said experiment spokesperson Viktor Zacek of the University of Montreal in a statement.

“However when we checked the data and refined the analysis the discrimination effect became even more pronounced,” he said.

It’s like trying to hear a friend (a WIMP) talking to you in a noisy bar, when someone else with a similar voice (an alpha particle) is shouting next to you. This new technique will allow scientists to essentially filter out the similar voice, allowing them to hear their friend’s voice.

While this isn’t an actual detection of a dark matter particle, it’s a nice solid step in that direction. Remember, scientific progress isn’t usually just waking up one day and realizing you’ve overthrown the leading paradigm. It’s usually a series of small progressions, a journey of a thousand steps. Each movement forward is important, and when taken in total, they take you along the path to your goal: understanding the Universe. Lots of people say it’s not the goal, it’s the journey that’s important. While I think this goal is pretty important, in this case the journey itself can be cool, too.

Tip o’ the axion to BABloggee sooz.

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

Comments (27)

  1. (a weakly interacting massive particle, or WIMP)


  2. PG

    so MACHOs (massive compact halo objects- dontcha love astronomical acronyms?) have been ruled out?

  3. Jerome Drexler

    A recent Amazon.com book review, by Dr. Chris Dyball, of Jerome Drexler’s March 2008 book, “Discovering Postmodern Cosmology,” adds to some of the preceding points regarding dark matter: “This third book in a series by Drexler shows how his thesis, that dark matter is composed of charged ultra high energy relativistic protons, is capable of solving up to 25 previously unresolved mysteries of the Cosmos. Older cold dark matter concepts, now generally discredited, relied on too few observations and have required additional hypotheses to account for each new experimental finding. In significant contrast: each new data set gathered subsequent to Drexler’s first publication of his thesis has appeared to reinforce his concepts without the need for adaptation. Most recently the publication by astronomers at the University of Chicago titled ‘Reopening the window on charged dark matter’ which occurred 6 months after Drexler’s third book first became available, lends considerable additional support to the thesis that dark matter is composed of charged particles. While this book is sure to prove controversial amongst conservative astrophysicists, I would encourage the reader to keep an open mind. Remember there was a time when conventional wisdom had it that the sun revolved around a flat earth!”

  4. Sarcastro

    Isn’t the similarity between these supposed WIMPs and Alpha Particles itself a fairly interesting?

  5. Is it really a big tank of water? I thought it was, in essence, a big tank of dry-cleaning fluid.

    Seriously, no?

  6. If there were rogue planets, wouldn’t we have invaded them by now?

  7. Don Cates

    It uses a big tank of heavy water on loan from Atomic Energy Canada which they collect for use in their CANDU reactors.

  8. tiureti

    SNO is indeed a tank of heavy water. Or was, as it’s now filled with regular water. The experiment they’re actually talking about in this article is not SNO. It’s an experiment called Picasso. Picasso is another experiment located in the same laboratory as SNO, called SNOLab. However, they are completely different experiments.

  9. tiureti– Ahhh, I see. I was wondering about that. The websites I was looking at were talking about the water, but had also said the tanks were currently dry for a refit. I decided this experiment was in the main tank, but the article was unclear. Thanks for the help.

  10. Utakata

    BA Wrote:

    “One such detector is in Canada. Or, rather, below it. The Sudbury Neutrino Observatory is essentially a big old tank of water, located over a mile underneath the Canadian landscape. Shielded by solid rock, the detector is designed to look at neutrinos, ghostly particles created during some particle interactions. In fact, SNO was crucial in solving the Solar Neutrino Mystery.”

    If you look close enough…you might find a few Liberal MP’s buried there as well.

  11. Davidlpf

    Didn’t know machos were ruled out, but I guess you learn something new everyday.

  12. Jose

    I don’t think MACHOs are ruled out as a source of dark matter. It’s just they could only contribute to a very small fraction of it.

    On another note, I’m sick of all the macho wimps out there. They’re all talk.

  13. David Taylor

    Compact solid objects with masses similar to ordinary household washers or dryers might do the trick. Such could have enough mass without having sufficient surface area to be detected by either radiation or occultations. Their individual masses would have no noticable individual dynamic effects.

    Any that ventured into inner solar system might get slung out into the Oort cloud – they might be the smaller elements of the Oort cloud – what evidence is their for an outer edge to the Oort cloud.

    I doubt, regretfully, that they actually are discarded washers and dryers. But then, who knows. Disposal of used appliances may be a problem elsewhere, too…

  14. Davidlpf

    I always thought it was a combination of MACHOS and WIMPS.

  15. “However when we checked the data and refined the analysis the discrimination effect became even more pronounced,” he said.

    I really love this quote, as it highlights one huge difference between science and pseudoscience. With a real effect, when you get suspicious and tighten the controls, the effect becomes more pronounced. With a false effect, it becomes less so. This is what people performing experiments on psi/homeopathy/acupuncture/etc. never seem to get. They simply pick out the poorer experiments and hold them up as proof, neglecting the fact that science doesn’t work that way.

  16. ChazInMT

    Hair brained idea here…..If Dark Matter has a repulsive effect on regular matter, wouldn’t it be cool to just gather up a big lump of it, put it in the trunk of your car, and Tada…flying car. (obviosly over simplified, but you get the drift.) Think of all the money we’d save in not having to overcome lift induced drag. Think of the drag it would be if you didn’t balance it out quite right….Next stop: Pluto!

  17. Kyle

    Do you have some insight on how Dark Matter is related to the Cosmic Inflation Theory? It seems that if Dark Matter was created as a result of the false vacuum, then these particles cannot be created by simply smashing photons together, only in the false vacuum.

    It’s odd that all of the material I read on the LHC, inflation is never mentioned, even though it seems to be a really well supported theory. Maybe particle physicists are discounting it? Or maybe I’m reading the wrong articles 😛

  18. Me=not a scientist. I get my science via TED, Nova, interesting blogs and books by noted skeptical astronomers…

    Forgive my ignorance if it’s showing too much with this, but I watched a TED video describing dark matter and what the presenter described was stuff which behaved exactly the way Brian Green’s Elegant Universe describes gravity operating if brane theory were true. My question is, what if dark matter isn’t dark at all? What if it’s quite cheery, but we cannot see it because it’s not in our universe and only the gravity of the stuff is leaking through?

    TED video:

    Brian Greene program:
    (scroll down to “Escaping Gravity”)

    Again, I know nothing about this. I’m an actor and writer. I make stuff up. It just seems interesting to me (and I’m writing a story about it.)

  19. Aaron Gibbons

    Phil, how do we know that its simply not the usual space stuff that doesn’t emit EM radiation. Why is it not plausible to consider that Dark Matter unconsolidated dust, rocks, comits etc? Given their size and spread the vast real estate of the Universe that it would be infeasible to detect these particles but they would aggregate to something. If that was the case we might have to rethink our view that Hydrogen is the most abundent element.

    For example, the Oort cloud is shown to be there by calcuation but there is not way to see it. Given its distance the sun’s gravatational hold would be tenious and from that I would say there are more floating comits between stars than there are held by stars. Sure their mass (and therefore gravitational force) indivually can be rounded down to next to nothing but it could add up to something.

    We seem to think that most dust has settled into stars. Where is the proof to dispute to say that 90 per cent of it has not?

    And how about neutrinos? Buckets of these been emmitted ever since fusion started ergo, wouldn’t they add up to something?

    What about energy left over from the big bang/bounce? If energy and matter are interrelated proportionatly by c-squared, is is possible therefore that even energy in large quantities may in somewhay have gravitational attraction?

    I’m not an astronomer or a physicist but to me so I don’t have all the theories and deductions in front of me. But to me it seems people are thinking too hard about this.

  20. Davidlpf

    @aaron Gibbons
    neutrinos and small bits of matter probably make up some dark matter but there is probably not enough to count for dark matter in the universe.
    @ChazinMT since dark matter is interacting gravitationaly is probably attrave not replusive. I think you are confused with dark energy which is speeding up the galaxies seperation each other.

  21. Aaron Gibbons

    I never implied that nuetrinos would of accouted for all of the dark matter. Also, “probably” implies to me that there has been to date, insufficient research into this area. Do we really know how many of these things are out there?

    And what about all the other stuff I mentioned?

    And how come dark matter is so exotic but everywhere, how come there is not gravitational footprint of it in our solar system? If stellar winds push gases/dust out of their systems thus putting this stuff between stars then to me there is a base arguement to suggest that dark matter is simply loose gas/dust between stars (and maybe event galaxies) that hasn’t yet been given the time and opportunity to consolidate.

    Like I said, I’m not an astronomer or a physicist but I see so many questions pointing to the obvious which haven’t been fully explored.

  22. Davidlpf

    The other things probably are part of dark matter as well.
    Part of the problem is you do know how gravity works and also how these particles interact with matter. That is why these experiments like this and LHC are done.

  23. Phy

    You may have mentioned it before when talking about the Sudbury Neutrino Observatory, Phil, but I thought I’d bring it up: The mine in which SNO is situated was excavated to gain access to a great walloping nickel deposit, one which formed in the aftermath of a great walloping meteor impact. The crater that formed, known as the Sudbury Basin, seems to be one of the largest known on Earth.

    So dark matter astronomy is taking place two kilometers underground in a facility that never directly sees the sky, sited knee-deep in the wreck of a monstrous and ancient meteor strike.

    How cool is science again?

  24. madge

    Cool post BA. I studied the SNO during my particle physics course and am hoping to visit the Boulby mine, just up the coast from me where they are also looking for dark matter. I love this stuff!

  25. Gary Ansorge

    The OORT cloud does in fact interact with normal electromagnetic radiation by absorbing/scattering it. It’s just far enough away and of such low density we don’t get to see much of that interaction. Over interstellar distances there’s enough dust/small masses for us to readily detect that interference. Over intergalactic distances, dust/normal matter displays its interference quite well but dark matter is detectable ONLY by its gravitational effects, not by absorption or scattering of EM.
    We are looking for dark matter close to earth, but it’s estimated that there would only be a few particles/Cm^3, which makes detecting it really hard, especially since we can’t see it in the EM range however, we are working on it.
    It’s a little like looking for a mirror in an unlit room. You’ll know it’s there when you trip over it,,,

    GAry 7

  26. Jesper

    So you’re in a bar, and there is an alpha male shouting around, while you’re trying to listen to what the shy wimp is saying…

  27. Torbjörn Larsson, OM

    dark matter is composed of charged

    Dark matter doesn’t EM interact (measurably); try again.

    inflation is never mentioned, even though it seems to be a really well supported theory.

    AFAIK it isn’t well supported yet, say, by any single 3 sigma experiment predicted by theory. OTOH AFAIU it resolves many problems and fits naturally with sundry theories.


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


See More

Collapse bottom bar