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Space Science

Cosmic Antimatter Excess Confirmed 113

Posted by Soulskill
from the good-news-for-warp-core-engineers dept.
sciencehabit writes "In 2008, the Italian satellite PAMELA picked up an unusual signal: a spike in antimatter particles whizzing through space. The discovery, controversial at the time, hinted that physicists might be coming close to detecting dark matter, an enigmatic substance thought to account for 85% of the matter in the universe. Now, new data from NASA's Fermi Gamma-ray Space Telescope confirm the spike (abstract)."
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Cosmic Antimatter Excess Confirmed

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  • by Anonymous Coward on Wednesday November 23, 2011 @06:15AM (#38146620)
    I'm confused, is this about antimatter or dark matter?
    • Re: (Score:2, Informative)

      The answer is in the second paragraph of the article.

      • by Anonymous Coward on Wednesday November 23, 2011 @06:33AM (#38146702)

        The answer is in the second paragraph of the article.

        Well, don't keep us hanging in suspense here! What does the second paragraph of the article say?!?

        • by justin12345 (846440) on Wednesday November 23, 2011 @06:43AM (#38146756)
          "Theorists generally believe that when two dark matter particles collide, they should annihilate each other to produce ordinary particles, such as an electron and its antimatter twin, a positron. Thanks to Einstein's iconic equivalence between energy and mass, E=mc2, each of those particles should emerge with an energy essentially equal to the mass of the original dark matter particle."

          I suspect that the author doesn't know that "dark matter" isn't a synonym for "antimatter". The above paragraph, if true, would make the universe a very explode-y place.
          • by mattie_p (2512046) on Wednesday November 23, 2011 @06:48AM (#38146776)

            "Theorists generally believe that when two dark matter particles collide, they should annihilate each other to produce ordinary particles, such as an electron and its antimatter twin, a positron. I suspect that the author doesn't know that "dark matter" isn't a synonym for "antimatter". The above paragraph, if true, would make the universe a very explode-y place.

            Some dark matter candidates are, according to theory, their own anti-particle. The only reason it is not a more explode-y space is that dark matter interacts very weakly with other matter, including itself, and therefore has not been identified yet.

            • by rossdee (243626) on Wednesday November 23, 2011 @08:14AM (#38147076)

              "Some dark matter candidates are, according to theory, their own anti-particle"

              In related news, Herman Cain is his own worst enemy.

            • Some dark matter candidates are, according to theory, their own anti-particle. The only reason it is not a more explode-y space is that dark matter interacts very weakly with other matter, including itself, and therefore has not been identified yet.

              That would make dark matter very lonely. If it interacts weakly, wouldn't there need to be more of it to account for the effects that dark matter was invented to explain?

              • by Surt (22457) on Wednesday November 23, 2011 @12:04PM (#38149138) Homepage Journal

                It was mainly invented to explain why the amount of gravitational effects observed exceed the amount of mass visible. If dark matter has normal gravity, but interacts with other matter in an otherwise very limited fashion, then, no, there wouldn't need to be more of it.

              • by dmartin (235398) on Wednesday November 23, 2011 @12:21PM (#38149382)

                Some dark matter candidates are, according to theory, their own anti-particle. The only reason it is not a more explode-y space is that dark matter interacts very weakly with other matter, including itself, and therefore has not been identified yet.

                That would make dark matter very lonely. If it interacts weakly, wouldn't there need to be more of it to account for the effects that dark matter was invented to explain?

                Gravity is incredibly weak for individual particles. The reason we notice it in everyday life is because there are a lot of particles in the Earth pulling us the same way and all those little bits add up. This is the bit that we rely on to explain the galactic rotation curves (and to explain the cold spots in the CMB). If the dark matter only interacted gravitationally then it would almost impossible for us to make any direct detection of this sort (but it is also difficult to explain how so much of it was produced).

                The idea of the WIMP is that the dark matter, in addition to interacting gravitationally, also interacts via another force called the weak force. While these interactions would have to be somewhat small so that the dark matter did not all explode, or collide too much with itself, it would still be much much stronger than the gravitational interactions on a per particle basis -- but would not "add up" the same way. [As a very simple analogy, the electric forces between protons and electrons are very strong compared to their gravitational attraction, but on large distances matter is almost neutral because opposite charges attract]

                This idea is appealing to physicists because
                    1) if true, we have hope of detecting the dark matter and verifying its existence and
                    2) it tells us (very broadly) that we would produce the right amount of dark matter as the universe was cooling (the so-called WIMP miracle)

                • by Anonymous Coward

                  I'm missing something here. I thought one of the greatest (theoretical) achievements of the last century was the unification of electromagnetism and the weak (nuclear) force (i.e. they are mediated by the same charge carrier). How does dark matter fit in with this view, if it does not interact EMically yet does respond to the weak force?

          • by sheepe2004 (1029824) on Wednesday November 23, 2011 @07:17AM (#38146892) Homepage
            Why is this modded +4 informative? The quoted text doesn't confuse dark matter and antimatter. The universe isn't explode-y because (if the theorists are right) dark matter interacts very weakly and so collisions are very rare.
            • Re: (Score:2, Interesting)

              by justin12345 (846440)
              Just think about the amount of energy that would be present in such a system. If two (nebulously defined) particles of dark matter can annihilate (probably the wrong word) each other to produce a particle of antimatter and a particle of matter, it follows that the dark matter particles must be as massive as regular matter/antimatter. So they wouldn't be very weakly interactive. And that's even assuming that absolutely no mass is converted to energy when the particles "annihilate" one another, which is unlik
              • by MrZilla (682337) on Wednesday November 23, 2011 @08:53AM (#38147256) Homepage

                I think you are confusing "massive" and "strongly interacting".

                The whole point of "dark matter" is that it interacts gravitationally with ordinary matter, but almost never in any other way. So, having massive dark matter particles means a higher gravitational field around them, but nothing else.

                I agree with your other point however, that having two of these dark matter particles annihilating directly to a electron/positron pair seems.. strange. Normal matter/antimatter annihilations always (afaik) produce "energy" (i.e. photons).

                But a good thing is that if annihilation of dark matter produces electron/positron pairs, then smashing electrons and positrons together in an accelerator should produce dark matter.

                • The photons were probably simplified out of the explanation. If the article would report everything, it would be talking about momentum, and virtual particles too. They probably annihilate into a photon, that produces a pair of electron/positron, and that pair is separated by Earth's magnetic field.

                  Also, they probably didn't detect the positrons, but some photon generated by its annihilation.

                  • by Roger W Moore (538166) on Wednesday November 23, 2011 @02:29PM (#38150692) Journal

                    If the article would report everything, it would be talking about momentum, and virtual particles too.

                    It would not report on virtual particles because the annihilation takes place in the galactic core where the densities of DM are highest and virtual particles can only exist for the tiniest fractions of an instant not the ~50k years needed to make it from the core.

                    The question you should be asking is where are all the anti-protons? Since DM particles generally need to have masses roughly ~100 or more times the mass of the proton their annihilations should be capable of producing all stable anti-particles below this. Hence most models predict an excess of anti-protons as well as positrons but no satellite has seen any evidence of this. So if this positron excess is due to DM (and that is a BIG if!) we may have to start looking at some of the more exotic DM models (e.g. Arkani-Hamed et al. Phys Rev D (2009) vol. 79 (1) pp. 015014) which some of us are already looking for with the LHC.

                • by Anonymous Coward on Wednesday November 23, 2011 @09:06AM (#38147338)

                  Anything which can produce photons also can produce electron-positron pairs, just with lower probability. However dark matter particles should not produce photons directly because they don't interact electromagnetically (the defining property of dark matter!), and annihilating (directly) into photons would be an electromagnetic interaction (photons are not "pure energy", no matter how often you read that). Rather as weakly interacting particles, I'd expect them to produce virtual Z0s which then could decay into (real) electron-positron pairs, assuming sufficient energy (I'd expect the dominant decay channel to be into neutrinos, though).

                  • by MrZilla (682337)

                    Thanks for the explanation. I must admit my particle physics is very weak (not that that will stop me from commenting..)

                    I can not remember ever having seen an example where an annihilation produces anything other than photons, but I guess it's usually simplified that way for us laymen. Anyways, it makes sense now that I think about it.

                    • by geekoid (135745) <dadinportland AT yahoo DOT com> on Wednesday November 23, 2011 @12:22PM (#38149396) Homepage Journal

                      (not that that will stop me from commenting..)

                      and that is what's wrong with the world.

                      I don't know jack abut the subject, but I'll be damned if that stopped me from commenting like I'm an expert.

                    • Take a step back, take a deep breath, and get a little perspective. You're complaining about a lack of expertise on a website that allows anonymous posting, where the standard is semi-anonymous posting. No experts to be found there. You are commenting in a thread about dark matter, which is called dark because very little is known about it. No experts on that either. You are also commenting in a sub-thread which only purpose is to call into question whether the author of the article is confused by the termi
                    • by izomiac (815208)
                      Was the world really that much better during feudal times, where only the elite were educated and therefore the only opinions that counted?
                    • by MacDork (560499)

                      (not that that will stop me from commenting..)

                      and that is what's wrong with the world.

                      I don't know jack abut the subject, but I'll be damned if that stopped me from commenting like I'm an expert.

                      Welcome to every climate change discussion on slashdot.

                    • by tehcyder (746570)

                      Was the world really that much better during feudal times, where only the elite were educated and therefore the only opinions that counted?

                      On slashdot that isn't just a rehtorical question. A lot of the right wingers would say "yes" because obviously they would be in the eltie and there was minimal evil government to distort the true nature of society.

                • You're right, I was using the term "strongly interactive" incorrectly.
                • I think you are confusing "massive" and "strongly interacting".The whole point of "dark matter" is that it interacts gravitationally with ordinary matter, but almost never in any other way. >

                  Well, that explains a lot. This is why we can't find the elusive Higgs boson, they're obviously all out there in deep space hiding as dark matter!

              • I'm not a particle physicist but, from wikipedia: [wikipedia.org]

                The main theoretical characteristics of a WIMP are:
                Interaction only through the weak nuclear force and gravity, or at least with interaction cross-sections no higher than the weak scale;
                Large mass compared to standard particles (WIMPs with sub-GeV masses may be considered to be light dark matter).

              • by yndrd1984 (730475)

                If two particles of dark matter can annihilate each other to produce a particle of antimatter and a particle of matter, it follows that the dark matter particles must be as massive as regular matter/antimatter.

                Well, some particular kind of 'regular' matter/antimatter particle, yes.

                So they wouldn't be very weakly interactive.

                Why?

            • by Anonymous Coward

              Why is this modded +4 informative? The quoted text doesn't confuse dark matter and antimatter.

              Probably because the people modding are fully aware that "antimatter" is a specific type of particle, and "dark matter" is a phrase we use instead of saying "a bunch of shit we don't have any clue about yet."

            • by Joce640k (829181) on Wednesday November 23, 2011 @09:38AM (#38147574) Homepage

              Why is this modded +4 informative?

              Because it saved millions of slashdotters from having to read TFA.

          • by Lumpy (12016)

            "I suspect that the author doesn't know that "dark matter" isn't a synonym for "antimatter". The above paragraph, if true, would make the universe a very explode-y place."

            Ohhh! I'm gonna sing the doom song!!!!

          • I thought the general view is that dark matter doesn't even interact with itself, except gravitationally.

          • by miketee (513478) on Wednesday November 23, 2011 @08:01AM (#38147030)
            Clearly, the author DOES differentiate between Dark matter, and antimatter (and matter). They use the terms to refer to different things: 2 Dark Matter particles BEFORE a collision, and a matter + antimatter particle AFTER it. If you meant that the particle/antiparticle pair would instantly annihilate (and the large amount of DM would cause many such annihilations), remember that the DM particles *collided*. IANA Physcist, but wouldn't momentum be conserved, and the 2 new particles move apart with the conserved momentum, preventing annihilation? Also there is the weak interactivity that others have mentioned.
          • by mcgrew (92797) *

            The above paragraph, if true, would make the universe a very explode-y place.

            I'd say it is an "explodey" place. Hell, there's a hydrogen bomb only eight light seconds away, and it's been exploding for over four billion years. Almost every twinkle in the night sky is a incredibly huge fusion explosion.

            • by Pope (17780) on Wednesday November 23, 2011 @12:43PM (#38149634)

              Eight light minutes, actually.

              • by tehcyder (746570)

                Eight light minutes, actually.

                Hold on, the guy's just said there's a hydrogen bomb that's exploding and you're quibbling whether it's eight seconds or eight minutes until we're all incinerated in a cataclysmic fireball of doom?!

            • The above paragraph, if true, would make the universe a very explode-y place.

              I'd say it is an "explodey" place. Hell, there's a hydrogen bomb only eight light seconds away, and it's been exploding for over four billion years. Almost every twinkle in the night sky is a incredibly huge fusion explosion.

              The street is an "explodey" [what is that word!?] place. There is a car 1 meter away, and it has been exploding oil for an hour now. Almost every noise you hear in a street is a powerful explosion.

              There is no reason to make it sound so scary. It is an ensemble of continuous, small, explosions that amass to a continuous energy output (not "explodey").

    • by mattie_p (2512046) on Wednesday November 23, 2011 @06:34AM (#38146706)
      I'm really confused. Dark matter is made out of spikes? Do they stab at thee from hell's heart or something?
    • by Greyfox (87712)
      What's it matter?

      Hmm wait...

      What's it, matter?

  • by ibsteve2u (1184603) on Wednesday November 23, 2011 @06:26AM (#38146668)
    ...zipping by to see if we've eliminated ourselves yet.
  • What I am afraid of, if anyone ever cared... ;)

    What I am afraid of is that some people will use this as evidence of otherworldly forces (any Slashdot reader), supreme beings (any Slashdot reader), Batman (a DC comic), demons (a variety of delusions), Thor (The Norse God), Bogeyman (an American tell tale), Akhenaten's Ra (Akhenaten the monotheistic precursor to the Abrahamitic monotheistic "Yahweh"), Santa Claus (The Coca Cola version of a Norse tradtion), Green Lantern (a DC superhero), Sherlock Holmes (a D

    • You live with the strangest of fears... Even if your fears are realized, so what?

      • by Anonymous Coward

        "You live with the strangest of fears... Even if your fears are realized, so what?"

        It could influence world politics. Imagine some part of the world where some would argue that their well being was given by some otherworldly power, and, that at least some fuck-ups would believe. It could create a situation where we would have a seriously lethal conflict that could go on for decades. inasity_rules, would that be a situation you wouldn't object to, the killing of innocents for any profound reason at all...

        • by Surt (22457)

          You feel that there isn't a sufficient amount of irrationality out there to generate wars now, but after dark matter is discovered, there will be a big increase?

    • by Anonymous Coward

      What, you didn't notice the paragraph further down the article?

      "As a technical feat, it is beautiful," says Harvard University physicist Doug Finkbeiner. Still, he says it's too soon to say whether the new data say anything about dark matter. [...]The new paper is "a wonderful confirmation of the PAMELA result," he says, "however the positron signal will likely be there whether the positrons come from dark matter annihilation, or from pulsars, or from tooth fairies."

      (emphasis added)

    • by Ricwot (632038)

      Surely a world with Sherlock Holmes would provide a good deterrent to criminals, or at least make their exploits really interesting reading for those of us who still read newspapers?

    • by Muad'Dave (255648)

      I'm worried about midichlorians.

      • by garaged (579941)

        They did not do any harm to Anakin....oh wait!

      • by mcgrew (92797) *

        No reason to, there are none in our galaxy, although I understand that the aliens in a far distant time in a galaxy far, far away have plenty.

    • by tehcyder (746570)

      Akhenaten's Ra (Akhenaten the monotheistic precursor to the Abrahamitic monotheistic "Yahweh")

      That's easy for you to say.

  • by gringer (252588) on Wednesday November 23, 2011 @06:31AM (#38146690)

    It doesn't matter

  • Ha, it's regional asymmetry and you know it ...
  • by walter_f (889353) on Wednesday November 23, 2011 @07:32AM (#38146948)

    In my opinion and in contrary to what the original posting suggests, anti-matter should not be viewed as particularly "dark".

    E.g., anti-Hydrogen, consisting of an anti-proton and a positron, will readily absorb a quantum of energy (a photon, which happens to be one of the particles that are their own anti-particles) and re-emit a photon again, just like "plain old" hydrogen. Thus, a cloud of anti-hydrogen should be observable as easily (or difficultly) as a cloud of hydrogen, assuming their masses, their viewing distances and all other parameters like temperature, density etc. being equal.

    So there should be no difference in observability here, due to the fact that photons are citizens of both realms, of "nornal" matter as well as of anti-matter, and will interact with mass particles of both realms in the same way.

    Obviously, "dark matter" looks like a very different beast...

    • by sheepe2004 (1029824) on Wednesday November 23, 2011 @07:50AM (#38146994) Homepage
      I'm guessing you didn't RTFA? They are not saying that antimatter is dark matter.

      They have detected a large and unexpected amount of antimatter.
      Dark matter collisions (theoretically) can create large amounts of antimatter.
      So one possible explanation for the antimatter is that two dark matter particles collided.
    • by expo53d (2511934)
      Interestingly enough, we could all be made up of antimatter. If after the Big Bang, the amount of anitmatter was greater than matter, we be made (assuming me happened to exist) out of anitmatter, but call the anitmatter "normal matter", and call the real matter "anitmatter".
      • Re: (Score:2, Insightful)

        by Anonymous Coward

        Interestingly enough, we could all be made up of antimatter. If after the Big Bang, the amount of anitmatter was greater than matter, we be made (assuming me happened to exist) out of anitmatter, but call the anitmatter "normal matter", and call the real matter "anitmatter".

        That's gibberish. You might as well says that cats might really be called dogs. They're not. Which is matter and which is anti-matter (or any other labels) depends on what names people have given them. There isn't a "right" answer outside of what people have come up with.

      • by Anonymous Coward

        You're the only that anti-matters here, dude.

      • Re: (Score:2, Funny)

        by Anonymous Coward

        Interestingly enough, we could all be made up of antimatter. If after the Big Bang, the amount of anitmatter was greater than matter, we be made (assuming me happened to exist) out of anitmatter, but call the anitmatter "normal matter", and call the real matter "anitmatter".

        Yeah! And how come we call them fingers if we never see them fing?

        • by Cragen (697038)
          Ha! Reminds me of the time I went to a talk by a Tibetan lama. He asked a question of the audience and requested that everyone who thought the answer was "yes" to "raise your arms." I had to do a mental double-take to get back to the question. :) (In the USA, our expression is "raise your hands".) Good to get my brain nudged from its nap every now and then.
          • by tehcyder (746570)

            Ha! Reminds me of the time I went to a talk by a Tibetan lama. He asked a question of the audience and requested that everyone who thought the answer was "yes" to "raise your arms." I had to do a mental double-take to get back to the question. :) (In the USA, our expression is "raise your hands".) Good to get my brain nudged from its nap every now and then.

            What's the problem, I don't see how you could raise your hands without raising your arms anyway.

  • by orphiuchus (1146483) on Wednesday November 23, 2011 @08:48AM (#38147234)

    What is mind?
    No matter.
    What is matter?
    Never mind.

  • So... Are there any theories on how to create a dark matter powered electricity generator?

  • by AdrianKemp (1988748) on Wednesday November 23, 2011 @09:12AM (#38147374)

    Antimatter galaxies (or at least clumps) seem like they could also plausibly explain this. That's not an outright endorsement of the theory but I can't help but think that they've got insufficient evidence to show causal link.

    They're saying:
    1. lots of energy released (presumably when dark matter interacts)
    2. anti-matter is created

    An equally plausible interpretation is:
    1. the anti-matter already exists
    2. the interactions with small amounts of matter cause the energy release

    I may have missed it, but I don't see anything to rule that possibility out. The primary objection to the anti-matter galaxy theory is that we don't see a lot of annihilation events; This could just as easily be those exact events.

    • They are detecting those events on the Earth magnetic field, not some distant point of the Universe. So, I guess no, if it was an ati-matter galaxy, we'd have detected it already.

      • Wait, unless I've missed something you just made an incredibly silly argument. They've detected something for the first time; whatever the explanation for the event is, saying "they'd have detected it already" is broken.

        • That anti-matter was detected here, on Earth's magnetosphere. If it comes from some anti-matter cluster, it would be newby and we'd be able to see it annihilating with the nearby matter, what means, with us. Or better, we'd probably not be able to see anything anymore.

          • Can you point to where that's said? From what I read they used the earth as a filter to block out noise, I saw nothing regarding the events happening locally

            • "They found a way to do so, using Earth itself as a particle filter. "You can basically look in certain directions from which only electrons or only positrons will get through the Earth's magnetic field," Vandenbroucke says. "

              So, altough their model says the interesting events happened farther away, the anti-matter that they are detecting is quite here.

    • Antimatter galaxies (or at least clumps) seem like they could also plausibly explain this.

      Doubtful. As I understand it, after the big bang, the universe was so hot that matter couldn't exist. As the universe expanded and cooled, nucleosynthesis happened, and essentially, all the matter in the universe was created. At this point the universe was fairly uniform and matter and anti-matter were well mixed. They continued to annihilate, reform, etc as the universe continued to cool, but matter is created slightl

  • by Stirling Newberry (848268) on Wednesday November 23, 2011 @09:58AM (#38147738) Homepage Journal
    The most promising wimp is a particle known as the neutralino. This is a hypothesized particle which would exist in either super-symmetrical theories. Super-symmetry says that in an unbroken general theory, every boson - a particle like a photon with an integer spin - has a fermion - 1/2 spin - partner, with the difference being that the fermion has a spin of 1/2. Since we don't seen bosons and fermions of the same energy, if, and it is still if, there was super-symmetry, it is a broken symmetry.

    The neutralino would be a composite particle, composed of the super-partners of the guage bosons and the higgs - that is wino (w partner), higgsino (higgs parnter), bino (partner of the weak hypercharge). Since the symmetry is broken, we don't see the original super-partners, only their super-imposed forms with the same mass eigenstate.

    When particles annihilate, they produce a set of particles that have a quantum number of 0. Any particles with the same mass-energy as the original colliding pair of particle and anti-particle can be produced. If mass energies are low, this means that the result will be mostly photons, because photons have no mass, and are only energy. That is, they have a low total mass energy. But any particles can be produced, so long as the result totals to 0, and has the same mass energy.

    Neutralinos, as you would guess, from the term WIMP, are weakly interacting, and massive. That means that when a neutralino annihilates another, particles with greater mass energy can be produced.

    In a 1994 paper Drees et al [aps.org] calculated neutralino decay into gluons. One of the co-authors here Kamionkowski went on to publish more on dark matter and neutralinos. There have been other papers on other possible decay products from neutralino annihilation, because, of course, if annihilation produces unstable particles, or anti-particle pairs, it can keep going until it reaches an end state of stable products. However, not all anti-particle pairs produce annihilate, and if the products are stable, they go bouncing on their merry way.

    This means that anti-protons and positrons above the background, and at certain energy levels could be the signature of neutralino dark matter.

    Or to roll things back: one of the few ways, other than gravity, we can detect WIMPS is from their annihilations. To determine if, and if so, what, WIMPs are composed of, we have to look at the decay products of those events. The Pamela data shows that there is an excess of positrons, however, it does not show that this excess is from WIMP annihilation. The search for this spectrum is important for both large and small reasons: large because cosmology evolves based on mass, and small because neutralinos, if detected, tell us about the final broken super-symmetrical extensions to the Standard Model, and in turn tell us about the super-partners, and, in turn, about the partners. For example, we have not seen a higgs boson, but a neutralino is an eigenstate of a higgsino fermion, which implies a higgs boson to be partnered with. Back in the 1990's Drees et al published

  • I was under the impression that anti-matter came from dilithium crystals, not dark matter.

    Now red matter apparently makes black holes, which I guess are kinda dark.

    Anyway none of this makes any sense to me. I think we need some new TV show that has this sort of information in it.

    I mean if the hydrospanner ain't broke, don't fix it.

  • Good 'ol Slashdot. So many commenters who understand almost nothing about humankind's crowning intellectual achievement of theoretical physics and yet, with unbridled brio, are correcting the deficiencies in our current theory of dark matter and WIMPs in just a few lines here. We should all be thankful that Slashdotters are here to set the world's ignorant physicists straight! I'm looking forward to commenters coming up with the GUT and sorting out the European debt crisis for us as a side note, aren't y

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