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Space Science

Dark Matter Discovered Near Solar System? 179

Posted by Soulskill
from the near-being-a-relative-term dept.
gpronger writes "The ATIC (Advanced Thin Ionization Calorimeter) has potentially discovered the presence of dark matter close (only 3000 light-years) to our solar system. The system detected a large-amount of high energy cosmic rays which match the theoretical signature of dark matter annihilating itself. The universe is believed to be composed of about 25% dark matter, but there has been little evidence of it. This discovery, if correct, would be the first." The paper was published in Nature , but it requires a subscription to see beyond the abstract.
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Dark Matter Discovered Near Solar System?

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  • Re:zomg (Score:5, Informative)

    by Missing_dc (1074809) on Friday November 21, 2008 @08:14PM (#25854077)

    see http://www.xkcd.com/502/ [xkcd.com] for the joke

  • Re:math hosers. (Score:5, Informative)

    by blueg3 (192743) on Friday November 21, 2008 @08:20PM (#25854121)

    You have a background intensity that is a function of energy, B(E).

    Signal intensity is also a function of energy, S(E).

    The observed intensity I(E) is B(E) + S(E). The signal portion (observed intensity above background level) peaks at E = 650 GeV. At 800 GeV (and, one would assume, higher), the signal is small enough that the observed intensity is adequately explained only by background.

  • Re:math hosers. (Score:3, Informative)

    by slashdotlurker (1113853) on Friday November 21, 2008 @08:21PM (#25854133)
    No.
    They have an energy dependent signal.
  • by jd (1658) <imipak@nOSPam.yahoo.com> on Friday November 21, 2008 @08:53PM (#25854377) Homepage Journal
    It would be more correct to say we lack evidence for viable alternatives, assuming the current models used, for which we now lack evidence unless evidence has been lacking on the existence of dark matter. Which may be great for grant checks, but it's lousy science.
  • by EveLibertine (847955) on Friday November 21, 2008 @08:56PM (#25854391)
    The things that are considered "evidence" of dark matter are things that match prediction models of things that would happen because of dark matter. Fancy stuff like high energy cosmic rays of certain types and the like. The trick is that there are also may be other models that predict similar types of events that are used as evidence of dark matter, but these models are models that exclude the possibility of dark matter

    So, the evidence that points towards dark matter could also point towards other conflicting models of our universe, essentially being evidence for many different models at once. The reason discoveries of this kind of evidence is exciting is because it gives us something to look at and test so that we might select or eliminate from the groups of conflicting models.
  • Bad summary. (Score:5, Informative)

    by JohnnyDanger (680986) on Friday November 21, 2008 @09:05PM (#25854461)

    The summary misinterprets the results.

    The instrument detects high-energy electrons. They found an excess (only 70, but statistically significant) with a particular energy, which if they come from a galactic source (like a pulsar), that source must be within 3000 light years. However, the researchers can't find an appropriate source.

    Alternatively, this could be due to annihilating dark matter---the energy spectrum matches some models---but that's not necessarily coming from a particular source.

  • Re:math hosers. (Score:5, Informative)

    by Deadstick (535032) on Friday November 21, 2008 @09:17PM (#25854543)
    Did TFA just royally f**k up its math or something?

    No, their math is just peachy.

    A figure like 650 GeV is the energy of ONE cosmic ray. Think of a graph of the number of rays arriving per second versus the energy of the individual rays. You're getting this many 400 GeV rays per second, this many 500 GeV rays, and so on.

    What TFA says is that LOTS of 650 GeV rays were arriving from the newly observed source, and hardly any 800 GeV rays except for the background rate that you get from everywhere in the sky.

    rj

  • by ChromaticDragon (1034458) on Friday November 21, 2008 @09:21PM (#25854577)

    Interestingly enough, the universe is almost certainly much bigger than you believe.

    Honestly, we have no idea and probably no real way of determining how big the universe really is. Nonetheless, the observable universe seems to be at least 90 billion light years [wikipedia.org] in diameter. So, it'd be more like finding that random person in the same room.

  • by iris-n (1276146) on Friday November 21, 2008 @09:23PM (#25854597)

    What? Wild leap of faith, my friend.

    You are assuming that the universe is finite, and has been expanding at the speed of light from 15 billion years ago.

    Actually, the big bang occurred about 13.73 billion years ago, and from that you can calculate the radius of the visible universe, which is about 13.8 billion light years.

    The actual radius is unknown, as we don't know if the universe is finite or infinite, but it's at least 46 billion light years.

    But yeah, it's pretty close.

  • by C18H27NO3 (1282172) on Friday November 21, 2008 @09:33PM (#25854665)
    The current estimation is believed to be ~13.7 billion light years with a diameter of ~93Gly, (46 billion light years in any direction out from Earth).((Comoving distance, cosmologicaql time, et al.)) 3,000 LY would equate to roughly 17,635,876,119,550,800 miles. 46G LY would equate to roughly 270,416,767,166,418,000,000,000 miles.

    While not very close, it is a heck of a lot closer than if we were able to see it nearer the \edge\ of the observable portion of our universe.
  • Re:FTL Particles (Score:2, Informative)

    by xonar (1069832) <{xonar} {at} {smagno.com}> on Friday November 21, 2008 @11:31PM (#25855339) Homepage
    What about theoretical particles like tachyons? I was not sure if the article referred to anti-electrons commonly associated w/ anti-matter collisions (or is that a matter-antimatter collision). I am also not familiar with the basic nature of said particles, as I have only a casual interest in such physics. I was also stoned when I wrote that, the thought of aliens using a galactic standard FTL data transmission technique (unbeknownst to humanity, yet), peaqued my interest.
  • by NeoSkink (737843) on Friday November 21, 2008 @11:51PM (#25855425)
    No other theory works as well as dark matter (as part of LCDM) to explain obersavations. Other theories have to be changed to account for what we observe at pretty much every scale. Those that work for Galaxy rotation don't work for clusters, which don't work for lensing, which don't work for early structure formation, and so on. Sure, one or two pieces of evidence may favor one theory or another over dark matter, but LCDM fits in the vast majority of cases, far more than any other theory.

    Heck, you don't think that we scientists got together one day and said "I know, lets make up some goofy theory and then fudge the data to fit it!" do you? You do realize multiple theories were purposed, predictions were created, new data was taken, and conclusions drawn about which theories were supported by the new evidence, right? And that LCDM is the one that survived all the vetting? And that this process is still on going, yet LCDM still remains as the best theory?

    Just checking... See, that's sort of how science is supposed (and in this case does) work.
  • by rrohbeck (944847) on Saturday November 22, 2008 @12:09AM (#25855501)

    It seems that at least some dark matter particles are their own antiparticles since they can annihilate into gamma photons.

  • Re:FTL Particles (Score:3, Informative)

    by Tenebrousedge (1226584) <tenebrousedge@NospAM.gmail.com> on Saturday November 22, 2008 @01:03AM (#25855753)

    Being stoned is pretty good.

    The short answer is that that tachyons can't transmit information. The short explanation is that Einstein's theories prevent it.

    Anything with mass cannot reach the speed of light; it would require an infinite amount of energy. Anything without mass travels at the speed of light. Tachyons are obtained by throwing imaginary numbers into the mix.

    Dark matter is thought to be matter that does not interact with other matter except gravitationally. We don't have much of an idea what that would look like, but it would obey the rest of the physical laws as we understand them.

    If you have any other questions I can try to answer them. Wikipedia has a good article on faster-than-light [wikipedia.org].

    Also, I hope that you don't mind me correcting you, but the the word is 'piqued'.

  • by Ambitwistor (1041236) on Saturday November 22, 2008 @08:48AM (#25857245)

    Savain isn't a creationist, but he is a well-known physics crackpot. He's been promoting his B.S. for over a decade; just search the 1990s archives of the Usenet sci.physics.* groups. He emotionally can't accept the mathematical notion of spacetime, because he claims that "nothing can move in spacetime", which only proves that he misunderstands the whole concept. (Thus his claim above that physicists have been unable to explain the concept of "movement".) He usually then proceeds with long, profane rants against various respected physicists. You know you're on the receiving end of a classic Savain rant when he starts raving about "chickenshit voodoo physicists".

  • by Ambitwistor (1041236) on Saturday November 22, 2008 @08:56AM (#25857289)

    So shouldn't the longest distance to the far "edge" be 13.8 billion light years

    No, because spacetime is curved and the expansion rate is neither constant nor equal to the speed of light.

    The misconception is that the Big Bang was an explosion of matter into space, and there is some volume of space with matter in it and some volume outside of which no matter has yet reached.

    In modern cosmology, the Big Bang is an expansion of space. There is no center or edge of the universe (although there is an edge of the universe we can see, because light hasn't yet reaches us from farther), and matter is distributed more or less uniformly everywhere in space. More details in this FAQ [ucla.edu].

    Anyway, how can we go from that size to estimate how old it is? Because they expect it to expand at light speed?

    They look at the relationship between how far away objects are and how fast they're moving (via Doppler shift). This gives them the expansion history of the universe. Farther objects are older. Also, the structure of fluctuations in the cosmic microwave background radiation left over from the early universe depends on how the universe has expanded between then and now. When combined with the general relativity theory of cosmology and how the universe expands, you can back out an age estimate.

  • by Ambitwistor (1041236) on Saturday November 22, 2008 @09:04AM (#25857333)

    Space can expand at any rate, including faster than light. The FTL restriction is on matter/energy moving through space. It is not a restriction on the geometry of space itself.

    As for where the estimated age comes from, your own link answers that.

  • Re:math hosers. (Score:3, Informative)

    by blueg3 (192743) on Saturday November 22, 2008 @04:09PM (#25859955)

    Correct. That's what the article is saying -- it peaks at 650 GeV, and by 800 GeV is indistinguishable from background.

  • Re:FTL Particles (Score:1, Informative)

    by Anonymous Coward on Saturday November 22, 2008 @05:19PM (#25860331)

    Not really. The speed of light should been seen not as the speed that light happens to travel at, but a fundamental universal constant.

    From wikipedia:

    Special relativity reveals that c is not just the velocity of a certain phenomenon, namely the propagation of electromagnetic radiation (light)--but rather a fundamental feature of the way space and time are unified as spacetime. A consequence of this is that it is impossible for any particle that has mass to be accelerated to the speed of light.

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