Dark Matter's Profile Discovered?

pingbak writes "According to New Scientist, astronomers may have potentially discovered dark matter's EM profile (story). For the rest of us, this means astronomers may have just discovered all of the extra force holding the galaxy(-ies) together, which is not currently explainable though gravity and black holes at the center of universes alone. Since dark matter doesn't interact with ordinary matter, it's almost directly undetectable -- but now, physics and astronomy may just have had an awesome breakthrough. Nobel Prize material if it proves correct!"

Comments

Dark Matter Explaination?

[Randolpho]

Um... perhaps I'm very much misinformed, which is entirely possible, but the article submission makes the claim that Dark Matter doesn't interact with regular matter.

WTF? I thought the reason we're looking for Dark Matter is because the matter we *know* about doesn't add up to cause the gravetic interactions that we can observe. I thought Dark Matter was just matter we couldn't observe just yet, not some exotic "doesn't work the same as other matter" matter.

Am I totally wrong here?

Re:Dark Matter Explaination?

[Anonymous Coward]

Am I totally wrong here?

Probably not. It's a while since I did physics, but these dark matter theories to me sound like the epicyclic theories of the solar system of old. They are too convoluted to be natural IMHO. It's only in the last decade or so that telescopes (including the HST) have given us much insight into what's out there, along with the gamma ray observatories and orbiting infrared telescopes. Heck, we've only just figured out the Solar Neutrino Problem. I don't doubt the particle physicists will throw up some surprises eventually, but my hunch is that we still have a lot to discover with space-based telescopes across the whole range of the electromagnetic spectrum. This is wht orbiting gamma ray, x-ray, infra-red and optical observatories are important.

Re:Dark Matter Explaination?

[CheshireCatCO]

They've looked pretty hard and carefully for normal, baryonic matter to cause the effects. So far, little has turned up.

On the other hand, it's pretty clear at this point that dark matter in *some* form must exist. It's just a simple grasp of gravity coupled with some weird observations that lead to this conclusion. It is, in fact, very similar to the way Neptune was discovered. First, notice something odd about Uranus's orbit, then realize that another planet at position X could explain it. Just do it with galaxies and clusters, instead, and you start to suspect there's dark matter out there. Do some surveys and find that there doesn't appear to be enough brown dwarfs and black holes to make up the needed mass.

To be honest, while I'm a planetary scientist and thus obligated to make fun of cosmologists, I don't find dark matter, even heretofore undiscovered particles, that hard to believe. Not only is the evidence pretty good, it isn't difficult to imagine that we've only scratched the surface of what is out there. You suggest that we're just finding "what's out there" (a claim with which I might quibble). So why is hard to believe that we haven't found all of the particles in the subatomic zoo? Especially given that the ones we seek are, by definition, difficult to find.

And if you want "too convoluted to be natural", study quantum mechanics. It seems the universe doesn't care what we consider to be "natural", after all.

(And now, a few quibbles: the SNP was only recently really clinched with lab data, but people had speculated about the solution, neutrino oscillations, for quite a while before hand. The same is true of a lot of what HST and others have told us in the past decade: usually, they're helping refine our models and confirm our best guesses as to what's out there. So it isn't like astronomers a decade ago would be shocked at what we've learned.)

Re:Dark Matter Explaination?

[SEE]

In order for Newton's Law of Gravitation to work out with the observed orbit of Mercury, a new planet closer to the sun, generally called Vulcan, was postulated. It was never observed, but it had to be there, because of the gravitational effects.

Then Einstein showed we didn't understand gravity sufficiently, and his General Relativity eliminated the need for Vulcan.

In order for Einstein's General Relativity to work out for the observed motions of galaxies, dark matter and dark energy have been postulates. They've never been observed, but they have to be there, because of the gravitational effects.

Will someone else come along and show that we don't understand gravity sufficiently, and postulate a theory that will eliminate the need for dark matter and energy?

a little from column A, a little from...

[bscott]

What they mean by "weakly interacting" is similar to how neutrinos are described - it doesn't have much of an electromagnetic impression, so it doesn't block light or smack into a detector in an earthbound observatory. Unlike neutrinos, it does posess a significant mass and is affected by gravity. And while that is "exotic", astrophysicists were only forced to consider this sort of thing when all previous efforts to explain some pretty obvious mis-matches in the numbers didn't work.

Now I'll let someone else explain about "dark energy"...

Re:a little from column A, a little from...

[Anonymous Coward]

Dark Energy (IIRC, IANAP, etc): A property of empty space that causes it to expand. Current theories suggest the universe will have a cold death instead of a heat death because unlike gravity, dark energy doesn't fall off at a distance. So, everything in the universe that isn't close enough to be held together by gravity is being accelerated away from everything else.

Gotta love Astro/Quantum physics

[bill_mcgonigle]

So, two leading theories on Dark Matter are:

• it's a particle that's all around us, but has very strange energy levels and we've never detected it.
• there's no dark matter, just gravity intruding into our 4D universe from other branes, which we can't detect and can barely imagine.

Gotta love it. :)

Electronium?

[4of12]

IANAHEP, but is there anypossibility that an electron and a positron could orbit one another with a reasonably long half-life?

Re:Electronium?

[barawn]

Positronium.

It has a half-life of 0.1 uS. It's a relatively standard physics problem at the graduate school level to ask what the binding energy of positronium is.

If it ever comes up, it's (1/2) the binding energy of a hydrogen atom. The reasoning is simple - a positron and a proton have the same charge, but a positron and an electron have the same mass, so the "reduced mass factor" is 1/2, rather than 1. (M_p/(m_e+m_p) ~= 1) vs (M_e/(m_e+m_e) = 1/2).

Re:Dark Matter Explanation?

[Euphonious Coward]

If it was ordinary matter, it ought to make stars, or smash into other bits, and then we'd see it. When they say "weakly interacting", that includes gravity but not electromagnetics or nuclear forces.

The assumption that these photons have anything to do with dark matter, though, has more to do with fashion and funding than actual science. It's cool and helpful to have your new observation associated with something everybody's already keen on. What they do know, though, is that whatever's producing the photons is distributed like the galaxy's mass is, not like the visible stars are.

Neutrino's Big Cousin -- conclusions

[pbhj]

In the conclusions they appear to be saying that some new interaction is happening due to ('mediated by') exchange of a light gauge boson (translation: low-energy force-carrying integer-spin-particle)

Alternatively a new heavy fermion (neutrinos are fermionic, spin-1/2) mediates in the interaction: their words "could be responsible". So you might not be far off (if there second guess is correct).

Start talking Nobel prizes when CERN/Fermilab find either of these particles.

[... I've not done any particle physics for 5 years so this could be baloney.]

Re:I don't get it

[Royster]

There have been two leading candidates for dark matter: WIMPs and MACHOs. Each camp have had their proponents.

WIMPS: Weakly Interacting Massive Particles. Neutrinos on steriods. Since they only interact through the weak and gravitational forces, they are by definintion dark in EM. But, we haven't found any in colliders.

MACHOs: MAssive Cosmic Halo Objects. You're describing MACHOs. Ordinary, cold, dark matter. But there's probably too much of it to be this. It should have been swept up into stars.

Frankly, I think that the energy levels detected will prove to be not what we're seeking here. It's too much of a coincidence that it is the e/e-bar annilation energy. OTOH, if there were a WILP which did have such a mass, we'd probably never see it thinking we were looking at e/e-bar reactions.