Astronomers claim dark matter breakthrough

New Scientist ^ | 19:00 01 October 03 | Marcus Chown

[Ernest_at_the_Beach]

The identity of the Universe's dark matter may finally have been discovered. In what seems to be the most convincing claim for dark matter so far, researchers in England and France say gamma rays coming from the centre of our galaxy show hallmarks of these ghostly particles.

The research has only just been made public, so the team is still waiting for a response from other dark matter experts. But though the researchers are cautious, there is no hiding their excitement. "I've dropped everything else to work on this," says Dan Hooper of the University of Oxford. "We're really excited," adds his colleague Céline Boehm, also of Oxford. "I'm cautious but it's surprising everything fits so well."

The identity of the Universe's dark matter, which outweighs the visible stuff by at least a factor of seven, is the outstanding mystery of modern astronomy. Scientists think it must exist because its gravity affects the way galaxies hold together. But the particles do not emit any electromagnetic radiation so they have never been detected directly. No one knows what the particles are like, or exactly how they are distributed.

	Mystery cloud

However, because dark matter "feels" gravity like ordinary visible matter, it is a fair bet that it clumps in the centre of our galaxy. So the team turned their attention to a distinctive pattern of gamma rays coming from the centre of the Milky Way (see graphic). The sharp signal, which has an energy of 511 kiloelectronvolts (keV), is believed to be due to the annihilation of electrons and positrons ­ the antimatter equivalent of electrons.

Virtual standstill

But where did the electrons and positrons come from? People have speculated that the source is anything from the blast waves of a "hypernova" ­ a super-powerful supernova ­ to a neutron star or black hole. "But none of the explanations have seemed satisfactory," says Hooper.

[DannyTN]

Facinating, thanks for the post. Yet on the first reading I'm confused: Is dark matter light or just not heavy? And if it's light is that like a black light? And if it's not heavy, then there is a lot of it, then is it really dark or is it transparent?

It left me a little light headed and in the dark.

[baseballfanjm]

Could someone fill me in as to what dark matter is?

[NormsRevenge]

dark matter is what the Rnulled supporters have for brains.

[edwin hubble]

Dark matter... a description at this NASA link.

http://map.gsfc.nasa.gov/m_uni/uni_101matter.html

[Alas Babylon!]

[Chemist_Geek]

Whither the neutrino

Sure, just pop them into a 120 °C oven for five to six hours; they'll wither with all that H₂O boil-off...

;-P

[Colinsky]

Dark Matter is to the 20th and 21st century what Ether was to the 16th and 17th.

I think it's more like phlogiston--a colorless, odorless, invisible, indetectable substance that has whatever attributes are needed to explain the observations.

The observations show that the structure and rotation of galaxies do not fit our theories of gravity. Our theories of gravity also cannot be reconciled with the successful theory of quantum mechanics.

Heaven forbid that the theory of gravity should be re-examined. It's lots easier to think up fudge factors that would save the existing theory.

Two favorite kinds of dark matter are MACHOS (Massive Astrophysical Compact Halo Objects) and WIMPS (Weakly Interacting Massive Particles). I don't see how this new evidence can be reconciled with these theories. The inferred particles are way too small to be massive WIMPS, and the direction of the signal rules out the MACHO idea of invisible clumps of stuff orbiting the galaxy.

Even though we know less about gravity than any other force in the universe, people who question the standard theory are dismissed as crackpots, while those who propose ever more intricate imaginary structures and epicycles are considered the front edge of the field.

[swilhelm73]

Minor quibble -- but how can you "know" about something you've not detected? You can theorize about it, sure -- but that's not "knowing."

The gravitational effects of dark matter on a galactic scale has, IIRC, been pretty well established.

Basically, we can look at two galaxies in close proximity and establish the rough mass of both of them. We can then calculate, again roughly, the amount of 'light' matter, ie stars in them.

Those numbers are *way* off, by a factor of about 10 to 1. So, this seems to be proof that there is something with mass, and quite a bit of it, that we can't see.

[swilhelm73]

That's true, but we can see evidence of distant anti-muon production and even anti-proton production, so such energies are available. (The mass of a muon is of the same order of magnitude as this supposed dark matter particle.

Do we know what natural processes would create proton/anti-proton pairs? Or the same for muons? I know there are several that can lead to electron/positron pairs...but I don't remember running across the other two - or have we observed the particles without discovering the process creating them?

That depends on how strongly coupled it is to electromagnetic particles like electrons. If the coupling is small enough, there could be a fantastic holocaust of annihilation occurring all about you--even through you--and you'd never know it.

Well, wouldn't the enery released be about;

energy = 4*10^-28 kg * (3*10^8 m/s)^2

energy = 3.6*10^-11 J per annihilation pair.

Wouldn't that be enough to show up in any number of experiments as extraneously produced energy?

[r9etb]

Those numbers are *way* off, by a factor of about 10 to 1. So, this seems to be proof that there is something with mass, and quite a bit of it, that we can't see.

But that's not the same as "knowing" it's some sort of exotic stuff of the sort being talked about in this article.

[qam1]

Could someone fill me in as to what dark matter is?

It's whatever you want it to be.

[RightWhale]

Dark Matter is to the 20th and 21st century what Ether was to the 16th and 17th.

It might be so. Then there could be an experiment that would do to Dark Matter what Michelson-Morley did to the aether.

[chinche]

For physicists, if there is not enough matter (dark or otherwise) the universe will not eventually collapse. No collapse, no chance of eternity (see Barrow and Tipler). It is ultimately a religious question.

[Physicist]

Do we know what natural processes would create proton/anti-proton pairs? Or the same for muons?

Sure. Anti-protons would be produced as part of a hadronic fragmentation process, caused by the impact of high-energy protons. Muon pairs can be produced electromagnetically, just like electrons. Muons can also be produced from the decay of pi-mesons, which are produced copiously in hadronic fragmentation.

Wouldn't that be enough to show up in any number of experiments as extraneously produced energy?

But how is that energy manifest? It wouldn't be in the form of photons, because the dark matter particles don't couple to electromagnetism. Our energy measuring devices, which are electromagnetic, would be totally blind to whatever form of energy these things could emit.

For example, right this second, untold trillions of neutrinos are coursing through your body. There's quite a bit of energy there, but essentially none of it gets deposited in your body, because the neutrinos don't interact electromagnetically.

[baseballfanjm]

Special Dark is good, but I prefer milk chocolate.

[Fledermaus]

Thanks for the article. I always thought "dark matter" was that stuff between liberals ears.

[Fledermaus]

Is that like "Mystery Date"? I think my Mystery Cloud was a DUD!

[Fledermaus]

But it is all around us; we've known that for some time.

"Use the Force, Luke."

Sorry, I couldn't resist.

[qam1]

It might be so. Then there could be an experiment that would do to Dark Matter what Michelson-Morley did to the aether.

Well maybe, Maybe not
The ether was supposedly all around us so the "River" experiment could be done on earth while Dark Matter is conveniently in Galaxies far, far away.

[RightWingAtheist]

Even though we know less about gravity than any other force in the universe, people who question the standard theory are dismissed as crackpots, while those who propose ever more intricate imaginary structures and epicycles are considered the front edge of the field.

Actually, it's been pretty much known since it first came into being that the Standard Model is still an incomplete picture; the O'Raifeartaigh and Coleman-Madula Theorems demonstrated this in the late sixties and early seventies. It has, however, been extraordinarily successful at what it has been able to predict and explain, and supersymmetry and superstring theory have tried to accommodate it while explaining what has had trouble accounting for. I would highly recommend reading Gordon Parks's recent article on the Standard Model which appeared in Scientific American a while back, as well as his book Supersymmetry.

The Higgs Boson is my candidate for the ether of the 21st Century. If we find it, it will confirm the supersymmetry model. If it doesn't, it will force us to reconceive our picture of the universe drastically. Either way, the Standard Model will likely remain firmly in place, just as relativity and the null results of the Michelson-Morley experiment did not invalidate Maxwell's equations.