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cit.
"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," said Doug Clowe of the University of Arizona at Tucson, and leader of the study. "These results are direct proof that dark matter exists."



http://chandra.harvard.edu/press/06_rel ... 82106.html

a very important news!!!!

brunetto_64 wrote:
http://chandra.harvard.edu/press/06_rel ... 82106.html

a very important news!!!!

That news IS indeed important, and the methods used are VERY powerful:

a) gravitational (micro) lensing to locate the distribution of the gravitational field and hence of the luminous and dark mass in the colliding galaxy cluster(s),

b) the fact that luminous mass is mainly in hot gas within the colliding galaxy clusters

c) Finally, the complete simulation of this gigantic collision of the two galaxy clusters that results in a characteristic final distribution of luminous and dark matter in perfect agreement with the observations from the Chandra-X observations!

The crucial point is this:
------------------------
unlike luminous matter in the hot gas clouds, dark matter is known to interact very weakly with itself and with luminus matter (WIMPs!).
When the two galaxy clusters penetrate each other, their luminous matter distributions interact, are slowed down and tend to stick together, finally. On the other hand, the /weakly interacting/ dark matter distributions penetrate each other and continue without much distortion.

Hence this gigantic collision provides a characteristic SEPARATION
of dark and luminous matter in perfect agreement with observations.
Alternative theories (without dark matter, like MOND etc...) cannot reproduce the respective final matter distributions!

Bye Fridger

PS: Off I am again

Doesn't actually bring us closer to understanding what DM actually *is*, but it's interesting.

One thing that bugs me about all this - if DM is so common in the universe, why haven't we found any in our own Solar System? Surely there'd be some evidence of its influence here too? Or are our instruments just not sensitive enough to detect it here?

Malenfant wrote:One thing that bugs me about all this - if DM is so common in the universe, why haven't we found any in our own Solar System? Surely there'd be some evidence of its influence here too? Or are our instruments just not sensitive enough to detect it here?

That is a topic of ongoing research
e.g.
http://arxiv.org/abs/gr-qc/0602095

See also
http://hepwww.rl.ac.uk/UKDMC/dark_matter/wimp.html

Dark Matter kinda reminds me of the old idea of Ether... I guess that lives on in a different form

It's almost creepy that there's this *stuff* around us that we can't see or feel or touch or even detect beyond its gravitational influence on matter...

On an unrelated note, the background colour of that last link Selden posted is utterly horrible...!

Let me strongly emphasize that in particle physics, Dark Matter appears entirely naturally: there is absolutely nothing that reminds of the Ether etc.

That's the reason, why Dark Matter is so popular after all among scientists...

We are just talking about weakly interacting massive particles that do not have an electric charge, i.e. do not couple to photons, like neutrinos for example. There is nothing mystical or un-understood with neutrinos, except they happen to be ruled out as Dark Matter candidates for various reasons.

But there are natural candidates within Supersymmetry , or axion-like particles. The forthcoming LHC (Large Hadron Collider) at CERN in Geneva will be in the position to tell us which one of the candidates is the right one. In my laboratory, a decisive axion search experiment is planned for this fall.

So no doubt, we will know VERY soon.

Bye Fridger

PS: Off I am again

t00fri wrote:Let me strongly emphasize that in particle physics, Dark Matter appears entirely naturally: there is absolutely nothing that reminds of the Ether etc.

Oh I don't know, I think there is in the sense that most of the universe is something dark and mysterious and undetectable that normal matter is surrounded by. Maybe it's not "the medium through which light waves travel", which IIRC is what Ether was supposed to be, but if normal matter only represents 25% of the universe then it's not too big a stretch to imagine that our solar system is embedded in three more solar system's worth of dark matter, through which we all travel.

It's a not scientific comparison, merely reminiscent in some ways of the old ether ideas.

That's the reason, why Dark Matter is so popular after all among scientists...

So was Ether at the time .

Malenfant wrote:

t00fri wrote:Let me strongly emphasize that in particle physics, Dark Matter appears entirely naturally: there is absolutely nothing that reminds of the Ether etc.

Oh I don't know, I think there is in the sense that most of the universe is something dark and mysterious and undetectable that normal matter is surrounded by.

The point is that Dark Matter is detectable simultaneously yet independently in the Universe AND in the laboratory!

At colliders Dark Matter candidates can simply be produced and detected, like we can produce neutrinos and detect them beyond doubt.

Large enough amounts of Dark matter can be pinned down quite precisely through their gavitational effects in the Universe. (Micro) Lensing is one such method that is VERY powerful: From the observed shapes of the distortions/multiple images due to lensing and the known form of the gravitational field, the location of massive matter responsible for the lensing may be reconstructed. This method clearly detects non-luminous matter since it's gravitation not electromagnetism that does the job.

That's the reason, why Dark Matter is so popular after all among scientists...

So was Ether at the time .

Sure, but the crucial new aspect is that we can observe Dark Matter both in the cosmos and at colliders! That was hardly possible with the Ether . Finally, we shall know on a quite short time scale!

Bye Fridger

Here is the original paper about the direct, exciting evidence for Dark Matter via new weak lensing observations of the 2 huge colliding galaxy clusters 1E0657-558 (z=0.296)

http://cosmocoffee.info/viewtopic.php?p ... 1617fdf5cb

Below the paper you find respective opinions largely by cosmology experts and colleagues of mine, like Prof. Scott Dodelson from Fermilab/U. Chicago etc. Scott is the author of a recent, very popular book (Modern Cosmology, Academic Press 2003) that many of our PhD students have on their desks

We discussed the paper today extensively in my institute. It's really convincing and a most important discovery.

Here is the original weak lensing paper

http://arxiv.org/abs/astro-ph?papernum=408


Bye Fridger