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Profile Benjamin Wandelt
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Message 10809 - Posted: 17 Apr 2012, 23:21:43 UTC

Hi -

I hope you enjoyed our new featured concept on Dark Matter. Feel free to post your questions and comments here!

All the best,
Ben

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Profile Benjamin Wandelt
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Message 10834 - Posted: 20 Apr 2012, 13:14:54 UTC

Speaking of dark matter: almost on the same day we posted dark matter as the featured concept on C@H, ESO (the European Southern Observatory) came out with this hot news flash. Check out the

ESO press release

This would be pretty amazing if true. I have spent a couple of hours digging through the associated paper (which is linked from the press release) and while they seem to have done a thorough analysis, they also assumed quite a lot of information about the matter distribution in the galaxy.

Note also that their statement of "no dark matter in the solar neighbourhood" is incorrect. I am amazed that they chose to phrase it this way, since there are passages in the paper that show they know better.

Here is the point: their observational technique is not sensitive to a very smooth distribution of dark matter throughout the volume they probe. So they have no constraint on the overall amount of dark matter, just on gradients in the distribution. It is true that standard models of the dark matter distribution in galaxies involve an amount of dark matter that changes with distance from the galactic center, so it is true that they can constrain the standard dark matter models.

But the smallness of the constraint is very surprising and should be looked at by other groups.

Exciting times!

Best,
Ben



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Message 10836 - Posted: 20 Apr 2012, 15:33:48 UTC - in response to Message 10834.
Last modified: 20 Apr 2012, 15:59:44 UTC

Hello Professor Wandelt,

I was planning to ask you what you thought about the claims in this report, so I am glad that you have shared your thoughts with us.

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Message 10841 - Posted: 21 Apr 2012, 2:00:59 UTC
Last modified: 21 Apr 2012, 2:07:32 UTC

Question.

Based on two informations which i have heard of. Of course, i could have misunderstood something, so the whole idea could be nonsence.

Information 1:
We notice Dark Matter only because of its gravitational effects. Every attempt to search for dark matter is a method which is in some way related to gravitation.

Information 2:
The XYZ-Theory guys (M-Theory etc.) say, that gravitation could be the only force which could affect more than its own "membrane".

Conclusion&Question:
What about the thought, that there exists no dark matter overall?
The gravitation could be emitted completely by "normal" matter - of this and some (or all) other membranes (universes).

The idea is so obvious and simple that i am almost sure that i've got wrong informations or i didn't noticed/understand a logical error within it.
Makes this any sense?

Edit: Corrected "cykoenglish" mistakes
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Message 10844 - Posted: 21 Apr 2012, 21:56:24 UTC - in response to Message 10841.

Hi

Not at all a bad idea - in fact this is one of the proposed theories for dark matter, called the Dvalie Tye model proposed in 1998.

There is another idea that is similar in some ways called mirror dark matter. In this version another Universe is not necessarily involved. Here is the idea: if there are in fact not one but two copies of the standard model and particles in each are not allowed to interact with those of the other, then there could be a whole dark world out there, right in our universe, with dark stars, dark gaalaxies, dark people (?) and we would only know about it through its gravitational effects.

Note that our ordinary matter, including us, would be the dark matter to the other side. This symmetry is what led to the name mirror dark matter.

If that dark standard model were exactly like the one we know and love, then the Mirror Dark Matter model makes some interesting predictions, since dark matter would not be dissipationless in that model (it would be like ordinary matter interacting with the dark counterpart of the photon etc, so it could cool and condense into stars etc). These predictions lead to the model being disfavored observationally since the profiles of dark matter halos required to explain rotation curves seem to need to be much more extended than the ordinary matter.

But that's the way it should be for a real scientific theory: it should have falsifiable predictions! There is nothing as unsatisfying as a model or a paradigm that can shift and change to agree with whatever the observations come out to be...

In any case, congratulations - you had a serious scientific idea and there have been a number of papers and studies working out observational constraints on it!

All the best,

Ben

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Message 10848 - Posted: 22 Apr 2012, 1:33:39 UTC

Thank you Prof!
But what do you think? Which idea do you give (relative) best chance to be proven right? This lambda-something?
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Message 10859 - Posted: 22 Apr 2012, 23:01:11 UTC - in response to Message 10848.

Hi -

I am personally pretty agnostic about the nature of dark matter, meaning that I am not invested in any one particular model. I do think we need it. I also think that these are exciting times where a number of (disputed) hints are being confronted with an accelerated schedule of experimental and observational searches. Those look for direct detection of dark matter particles in (underground) labs, production of DM particles in particle accelerators (such as the LHC), as well as indirect evidence for dark matter from annihilations or decays (gamma rays, synchrotron radiation) that cannot be explained as coming from ordinary astrophysical origins.

Remember that we need dark matter for its gravitational effects, but all of these approaches are looking to get information about dark matter through its non-gravitational interactions, either directly or indirectly.

At the same time we are trying to resolve several puzzling questions about dark matter:
- what are the effects of the physical properties of dark matter on its spatial distribution, e.g. the density profile of dark matter clumps and the abundance of subclumps within larger clumps;
- what is the relationship between the distribution of dark matter and visible matter; and
- does dark matter have a (small but in some way noticeable) interaction with ordinary matter?

On that last question a recent conversation reminded me that 10 years on, my collaborators and I still hold the record for the most limiting constraint on baryon-dark matter interactions (Cyburt et al. 2002), at least in some energy ranges.

Nearly every month there is a paper claiming evidence for (or against as in this case) dark matter. This is truly one of the great questions of our time and what makes it even more exciting is that it has a real chance of being resolved in the near future. But I won't be more specific than that!

All the best,
Ben

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Message 10862 - Posted: 23 Apr 2012, 6:01:51 UTC

Thank you Prof. Lets hope that these exciting times will shine brighter than the otherwise exciting times in society and politics today :)
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Message 10872 - Posted: 23 Apr 2012, 21:46:34 UTC - in response to Message 10862.

I want to make a try to answer question No 3:
Dark matter (if it exists) interacts with ordinary matter of course. The both kinds seem to seperate from each other. If that wouldn't be the case, we would have on Terra more gravitation than mass. Correct me if i'm wrong, but i'm sure somebody has already checked that out. As far as i know, the solar system runs nice without dark matter.
If the both matters would not actively seperate from each other, the gravitation of both would have lead to mixtures of both, creating stars, planets etc..
Separation is interaction.

I'll post a german documentation Vid about our featured concept in Faiks Videothread

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Message 10899 - Posted: 25 Apr 2012, 16:29:07 UTC - in response to Message 10859.


Nearly every month there is a paper claiming evidence for (or against as in this case) dark matter. This is truly one of the great questions of our time and what makes it even more exciting is that it has a real chance of being resolved in the near future. But I won't be more specific than that!

All the best,
Ben


Speaking of claims of evidence against dark matter, here is a new article that discusses the implications of a new discovery on the quest for dark matter.

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Message 10904 - Posted: 25 Apr 2012, 17:18:28 UTC

Did i understand them right? They make Dark Matter theoretical obsolete, by just looking on the Milkyway at a higher point of view, like a bird flying higher?
And the outer borders of today are not the end of the gravitational construct "milkyway" instead of this they shall be somewhere in the middle which would explain the speed of their rotation?
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Message 10910 - Posted: 25 Apr 2012, 23:33:56 UTC - in response to Message 10859.

The field of cosmology is always full of surprises. In fact, there is the possibility that dark matter is something entirely different than what anybody has thought of before.

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Message 10915 - Posted: 26 Apr 2012, 5:11:42 UTC - in response to Message 10910.

In fact, there is the possibility that dark matter is something entirely different than what anybody has thought of before.


That is the beauty of science!

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Message 10989 - Posted: 2 May 2012, 3:34:59 UTC - in response to Message 10915.

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Message 11128 - Posted: 26 May 2012, 1:25:17 UTC
Last modified: 26 May 2012, 1:26:44 UTC

Hello I seen a program on Dark Matter, it's something that we all should take seriously. The way they explained it that dark matter is starting to appear very near. That our stars all being taken away by it.
Sorry I am new to your C@home, my name is Peter. I have my profile up. I hope I can help in anyway, I am on-line all the time.
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Message 11131 - Posted: 26 May 2012, 19:33:04 UTC - in response to Message 11128.

Dear Peter,

Welcome to Cosmology@Home!

I am not sure what TV program you have watched, but I was take most TV programs on scientific matters with a grain of salt. Dark matter is certainly something mysterious; however, I do not feel that it is as scary as you describe it :)

I hope to see you here often!

Best wishes,

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Message 11353 - Posted: 4 Jul 2012, 15:50:11 UTC

"...a real chance of being resolved in the near future..."

Higgs-Boson?
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Message 11523 - Posted: 31 Jul 2012, 23:14:22 UTC - in response to Message 11353.

Ok, so let me expand a bit on my comment in an earlier post "...a real chance of being resolved in the near future..." since it's now gone beyond just an insider rumor and there are a couple of more detailed science papers about it.

First in plain English: there is a real chance that a tell-tale signature of dark matter has now been observed.

Now in sciencese: a couple of analyses now see a line feature in the energy spectrum of gamma rays observed by FERMI satellite at an energy of around 129 GeV.

Why is this exciting? A line feature is exactly what would be expected if a massive particle annihilates and the release energy is liberated in gamma rays.

There are astrophysical sources of gamma rays as well, but they tend to be much more broad band, since the can produce gamma rays of a range of energies.

However, if two dark matter particles, each of mass 129 Gev moving at "normal" speeds (ie not close to the speed of light) run into each other then would decay at leastinto two other particles each carrying away 129 GeV of energy, and for symmetry reasons there would be no more and no less of that amount, leading to a well defined energy of the gamma rays. Counting up gamma rays detected by the Fermi satellite in bins of energy then leads to a big pile showing up in the 129 GeV bin - hence a line.

There are some who consider such a line signal a smoking gun of dark matter. And we may now have seen it.

One of the interesting properties of this line is that it is seen towards the galactic center (where there is a lot of dark matter but not away from the galaxy where we would not expect to see it if it were indeed dark matter. Also, the signal persists when the anaysis is re-done masking known astrophysical sources of gamma rays, just to exclude that some unknown mechanism, however unlikely, could produce such a line signal without dark particle decays being involved.

We had on of the authors of the first paper that found this line, Thorsten Brinkmann, at IAP a couple of months ago and we were all trying to pick apart his argument. In the end I thought it was pretty convincing.

Of course, it didn't take long for people to notice that this energy of 129 GeV was basically the same as the mass of the Higgs boson that was announced even more recently. Of course there are already model builders who are trying to explain this coïncidence.

Exciting times!

All the best,
Ben



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Message 11565 - Posted: 14 Aug 2012, 0:05:55 UTC - in response to Message 11523.

Here is a recent article which is relevant to the current discussion on dark matter: Plenty of dark matter near the Sun

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Message 12255 - Posted: 17 Dec 2012, 18:29:01 UTC - in response to Message 10809.

Has dark matter chirial properties?
If matter is dark and contains all wavelengths of light-has the 'darkness' smudged the resonant frequencies?
All the tests with neutrinos in chlorine tanks have presented little or no results despite been under controlled conditions underground-would they have smudged themselves with every day resonances?

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Message boards : Cosmology and Astronomy : Featured Concept: Dark Matter