Space Observatory May Have Found Dark Matter 145
KentuckyFC writes to mention that new data from the orbiting observatory PAMELA may shed some additional light on the question of dark matter. Still only a preliminary announcement, the new findings apparently support the "Minimal Dark Matter" model, in which a particle called a "Wino" is responsible.
Re:Again? (Score:4, Informative)
Re:Dark? Pls explain (Score:5, Informative)
The charged wino would not be a reasonable dark matter candidate for just the reason you give: it would interact with light and we would have detected it by now. The dark matter candidate should be uncharged and thus a partner of an uncharged particle, e.g. a zino or photino.
There's a terminology issue, however (here comes the boring part). The electromagnetic (photon) and weak forces (W+/- and Z) are understood to be aspects of a unified electroweak force. In electroweak theory its more convenient to talk of 3 W fields (+/- and neutral) and one neutral B field. The photon is a mixture of the neutral W and B, the Z is another such mixture.
The most common dark matter candidate (the lightest neutralino) is a mixture of the supersymmetric partners of these particles: the neutral bino and neutral wino (and two neutral higgsinos). We could just as well say that we're mixing the photino and zino (and two neutral higgsinos), but bino and wino are more common terminology.
The paper is speaking about a dark matter candidate which is primarily the neutral wino, with a little admixture of the other states. Note that this doesn't mean the dark matter is composed of multiple different particles, just that the one particle it is composed of is "in-between" these labels.
Re:Dark? Pls explain (Score:5, Informative)
I think the summary is just wrong. The arxiv article doesn't mention winos at all... perhaps the summary writer confused it with WIMP?
The DM canidate is specified to be a
in the article itself
Re:Again? (Score:3, Informative)
From TFA:
Yep, it's very much as you describe. Many of these models push the boundary of what can be called 'theory' in scientific terms, but they are the best we have so far. I think what's getting people excited is that the observations mentioned in TFA are predicted by a dark matter theory.
Re:Dark? Pls explain (Score:4, Informative)
Re:Again? (Score:5, Informative)
There's a big distinction between the general dark matter theory and particular candidates for dark matter. The general picture is supported by numerous different lines of evidence: not just galactic rotation, but by gravitational lensing, the microwave background, structure formation, etc. It has been much more successful than any modified gravity theory thus far. It's a good model thus far, and we'll drop it if other observations come along.
There are literally hundreds of specific theories of dark matter's composition, however, and those are individually on shakier ground. These are mostly particle physics models emerging from the 1980s. There are an infinitude of papers and preprint suggesting this or that candidate and what signatures it could generate. They do all make predictions, however, and our observations are getting good enough to test many of them. Between astrophysics and particle accelerators we have a real chance of figuring this out (and the PAMELA observation seems unusually interesting!)... but there are a lot of overblown claims in the media in the meantime.
Re:Again? (Score:5, Informative)
There is definitely such evidence - it comes from Big Bang Nucleosynthesis. The idea is that the light elements (deuterium, helium, lithium) were produced when the early universe had temperatures conducive to fusion. This phase only lasted a few minutes, and the abundance of the light elements today depends sensitively on the conditions during this period. The abundance of deuterium tells us pretty clearly that the total mass of matter (which affected the temperature profile during nucleosynthesis) was much greater than the total mass of ordinary matter (which participated in the fusion process). Similar evidence comes from the cosmic microwave background.
Astrophysicists did not initially want to believe that the missing matter was exotic, but there's some extremely compelling evidence!