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dreamregent
sage
Reged: 04/06/09
Posts: 454
Loc: Clearwater, FL
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What do you guys think of THIS?
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Building a f5.24 10" Dob
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matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10359
Loc: Chaville, France
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I'm certainly not an authority on the (dark?) matter, but I'd say that "extraordinary claims require extraordinary evidence". And that I'm getting wary of researchers using Dark Matter almost as a buzzword. You don't like the old explanation on Gould's Belt. So you invoke Dark MAtter. You don't know how Dark Matter can influence the formation of a ring of bright stars. And that does not give you an insight either into the nature of Dark Matter. How scientifically sterile is this? Using something you don't understand to explain something you don't understand?
Maybe USA Today is not doing a good job of reporting cutting-edge astrophysics and some salient points are missed in the article, but I'm not jumping out of my chair with this article.
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Matt
CI700 mount with various scopes on top.
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 12939
Loc: Amargosa Valley, NV, USA
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I have a problem with the theoretical concept itself: if Dark Matter is made of particles that don't interact much by other than gravity, then what is the mechanism that would hold such a cloud together as it passes through the galaxy? It seems that either the clouds would spread out and gravitationally mix together, or if dense enough, they would disrupt the galactic structure far more than simply creating a subtle ring of stars.
However, as Matt says, USA Today is probably not the best source to determine what the researchers are actually trying to say.
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"Since the process of science generates more mysteries than it solves, I predict that we'll never learn everything: and we'll continue to generate new ignorance at the speed of knowledge."
"S.O.E." (Sauron's Other Eye), with 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Under Construction: The "Eye of Sauron" Observatory!
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dreamregent
sage
Reged: 04/06/09
Posts: 454
Loc: Clearwater, FL
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Quote:
However, as Matt says, USA Today is probably not the best source to determine what the researchers are actually trying to say.
I would whole-heartedly agree but feel the need to point out that USA Today is not the source for the information. The paper is reporting on an article written by an apparent astrophysicist in a peer-reviewed journal. Does anyone know how to get access to the actual article on-line without having to pay for a subscription journal service? When I was in school, I had unlimited free access to most any journal and could read this kind of stuff to my heart's content but I'm not in school anymore.
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Building a f5.24 10" Dob
in an octagonal wood tube
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matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10359
Loc: Chaville, France
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The arXiv link only gives a synopsis, but it looks like here we are talking about "dark matter" and not necessarily "Dark Matter".
http://arxiv.org/abs/0906.5117v1
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Matt
CI700 mount with various scopes on top.
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astrotrf
professor emeritus
Reged: 09/30/07
Posts: 698
Loc: Rodeo, NM
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Quote:
I have a problem with the theoretical concept itself: if Dark Matter is made of particles that don't interact much by other than gravity, then what is the mechanism that would hold such a cloud together as it passes through the galaxy? It seems that either the clouds would spread out and gravitationally mix together, or if dense enough, they would disrupt the galactic structure far more than simply creating a subtle ring of stars.
Dreamregent, FWIW, I was able to get a copy of the paper simply by following the USA Today article link to the "Monthly Notices of the RASJ" which sends you to arXiv via scientificcommons.org.
Just from reading the abstract: the result was obtained by numerical simulation of an oblique high-speed collision between a million-solar-mass galactic gas cloud and a ten-million-solar-mass dark matter clump. The simulation, after the resultant induced star formation, created a ringlike structure of stars a la the Gould Belt.
(Ringlike structures like this are not unexpected -- see the Cartwheel Galaxy for a great example.)
The high speed and oblique angle would preserve the dark matter clump against gravitational dispersion, and, since the supposed collision happened only 30 million years ago, there wouldn't be a great deal of time for this additional mass to significantly disrupt the galactic structure. And this is to say nothing of the fact that the mass of the dark matter clump is only 1/100,000 of the mass of the Galaxy itself.
Finally, it is worth noting that the dark matter clump is not the authors' invention. Such clumps are, as the authors note, predicted leftovers of some models of galaxy formation. In the paper, they note that others have suggested a cloud-collision model for the formation of the Gould Belt. Their contribution, from my inexpert reading, is to show that such a dark matter clump could be the culprit.
So they are not attempting to invoke dark matter as a catch-all explanation, but rather demonstrating that dark matter clumps as already hypothesized are consistent with structures like the Gould Belt, and provide a handy explanation for such incoming high-mass clouds. (Though that's certainly not the *only* possible explanation -- Smith's Cloud will collide with our galaxy, too.)
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Terry (astrotrf)
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astrotrf
professor emeritus
Reged: 09/30/07
Posts: 698
Loc: Rodeo, NM
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Quote:
The arXiv link only gives a synopsis, but it looks like here we are talking about "dark matter" and not necessarily "Dark Matter".
At the upper-right corner of the arXiv abstract page, you'll see links that enable you to get the full paper in several formats.
And they *are*, in fact, speaking of "Dark Matter", since the paper references CDM (cold dark matter) cosmology.
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Terry (astrotrf)
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matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10359
Loc: Chaville, France
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Quote:
At the upper-right corner of the arXiv abstract page, you'll see links that enable you to get the full paper in several formats.
thanks! I missed it for some reason. OK Looks like something I have to read with my head down.
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dreamregent
sage
Reged: 04/06/09
Posts: 454
Loc: Clearwater, FL
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Quote:
At the upper-right corner of the arXiv abstract page, you'll see links that enable you to get the full paper in several formats.
Thanks. I saw the abstract but missed that as well.
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Building a f5.24 10" Dob
in an octagonal wood tube
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 12939
Loc: Amargosa Valley, NV, USA
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Quote:
Just from reading the abstract: the result was obtained by numerical simulation of an oblique high-speed collision between a million-solar-mass galactic gas cloud and a ten-million-solar-mass dark matter clump. The simulation, after the resultant induced star formation, created a ringlike structure of stars a la the Gould Belt.
(Ringlike structures like this are not unexpected -- see the Cartwheel Galaxy for a great example.)
The high speed and oblique angle would preserve the dark matter clump against gravitational dispersion, and, since the supposed collision happened only 30 million years ago, there wouldn't be a great deal of time for this additional mass to significantly disrupt the galactic structure. And this is to say nothing of the fact that the mass of the dark matter clump is only 1/100,000 of the mass of the Galaxy itself.
Finally, it is worth noting that the dark matter clump is not the authors' invention. Such clumps are, as the authors note, predicted leftovers of some models of galaxy formation. In the paper, they note that others have suggested a cloud-collision model for the formation of the Gould Belt. Their contribution, from my inexpert reading, is to show that such a dark matter clump could be the culprit.
So they are not attempting to invoke dark matter as a catch-all explanation, but rather demonstrating that dark matter clumps as already hypothesized are consistent with structures like the Gould Belt, and provide a handy explanation for such incoming high-mass clouds. (Though that's certainly not the *only* possible explanation -- Smith's Cloud will collide with our galaxy, too.)
OK, I get it now. High-speed oblique collision, relatively dense mass, and the collision is calculated with respect to the gas cloud alone, not with the entire galaxy.
I would suspect that, although this is possible and plausible, it's interesting in that such a collision would be suicide for the dark matter clump. I still think the gravitational tides of the galaxy itself would tend to pull it apart, maybe it could withstand a few such passes before spreading itself across the matter/dark matter distribution of the galaxy. Maybe this is how dark matter halos develop in the first place?
Are there any other examples known of galaxies that appear to have suffered a recent gravitational disruption with no sign of visible galaxies nearby?
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"Since the process of science generates more mysteries than it solves, I predict that we'll never learn everything: and we'll continue to generate new ignorance at the speed of knowledge."
"S.O.E." (Sauron's Other Eye), with 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Under Construction: The "Eye of Sauron" Observatory!
|
astrotrf
professor emeritus
Reged: 09/30/07
Posts: 698
Loc: Rodeo, NM
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Quote:
Are there any other examples known of galaxies that appear to have suffered a recent gravitational disruption with no sign of visible galaxies nearby?
Well, the Gould Belt is a fairly small structure on the scale of the entire galaxy, so I don't know that such structures would necessarily be obvious at galactic distance scales, especially given that projection onto the plane of the sky would tend to obscure any ringlike features. (I'm not saying they would necessarily be difficult to see; just that they might be difficult to unambiguously identify as gravitational disruption features.)
Secondly, the Milky Way is currently in the process of consuming at least a couple of small galaxies, there are other tiny galaxies nearby, and the Large and Small Magellanic Clouds are relatively close. From a distance, I'm not sure you could ever definitively say that none of the small galaxies near or within the boundaries of the Milky Way are responsible for some localized disruption feature.
That's all a long-winded way of saying "beats me".
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Terry (astrotrf)
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