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Lensman
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This article appeared March 2nd on Science Daily. Quite interesting. Any comments?
http://www.sciencedaily.com/releases/2012/03/120302101413.htm
http://www.sciencedaily.com/releases/2012/03/120302101413.htm
Tanelorn said:I agree this is interesting. I wonder if there is another way to confirm what we think we are seeing?
I understand that DM was postulated to explain the distribution of rotation velocities of galaxies, so if these Galaxies had been stripped of some of their DM would it not also show up in the galaxy rotational distributions?
The Bullet Cluster is claimed to provide the best evidence to date for the existence of dark matter (see for instance wikipedia entry). Is this new observation the best evidence to date against the existence of dark matter, then?Lensman said:This article appeared March 2nd on Science Daily. Quite interesting. Any comments?
http://www.sciencedaily.com/releases/2012/03/120302101413.htm
Not really. As I said, the vast, vast majority of clusters are very easy to understand in terms of dark matter. The bullet cluster is also easy to understand largely because it's easy to see what happened to separate the cluster gas from the dark matter. That a few clusters are difficult to understand in terms of dark matter is expected.TrickyDicky said:The Bullet Cluster is claimed to provide the best evidence to date for the existence of dark matter (see for instance wikipedia entry). Is this new observation the best evidence to date against the existence of dark matter, then?
Hmm, we are talking about clusters colliding here, do you know any good example besides the Bullet cluster and more recently MACSJ0025?Chalnoth said:Not really. As I said, the vast, vast majority of clusters are very easy to understand in terms of dark matter. The bullet cluster is also easy to understand largely because it's easy to see what happened to separate the cluster gas from the dark matter. That a few clusters are difficult to understand in terms of dark matter is expected.
There's this one as well, for instance:TrickyDicky said:Hmm, we are talking about clusters colliding here, do you know any good example besides the Bullet cluster and more recently MACSJ0025?
Yes, the ring one, CI0024+17, that makes 3 to one(Abell 520).Chalnoth said:There's this one as well, for instance:
http://www.scienceagogo.com/news/20070415204713data_trunc_sys.shtml
I don't quite see how, but I should mention that mirror matter is basically just one of many dark matter hypotheses. Mirror matter must be pretty different from normal matter in order to explain our observations, as dark matter interacts very weakly both with itself and with normal matter.johne1618 said:Maybe this is evidence for the "Mirror Matter" dark matter hypothesis.
http://en.wikipedia.org/wiki/Mirror_matter
Mirror matter is hypothesized to be just like ordinary matter but is "right-handed" rather than "left-handed".
Perhaps most mirror matter is in the form of mirror Hydrogen and mirror Helium which forms clouds around galaxies whereas some mirror matter might be in the form of heavier mirror elements that clump together.
Chalnoth said:I don't quite see how, but I should mention that mirror matter is basically just one of many dark matter hypotheses. Mirror matter must be pretty different from normal matter in order to explain our observations, as dark matter interacts very weakly both with itself and with normal matter.
Our best constraints on the interaction of dark matter with itself and with normal matter comes from the early universe, where all of the normal matter was an ionized plasma. At that time, the dark matter still didn't interact much at all with itself or with normal matter, so it can't simply be made of the same stuff as normal matter is.johne1618 said:If mirror matter exists and is mostly in the form of cold mirror hydrogen/helium surrounding galaxies then I suppose it would not interact strongly with itself if those galaxies collide.
Is that correct?
Chalnoth said:Our best constraints on the interaction of dark matter with itself and with normal matter comes from the early universe, where all of the normal matter was an ionized plasma. At that time, the dark matter still didn't interact much at all with itself or with normal matter, so it can't simply be made of the same stuff as normal matter is.
Well, at least not precisely. It basically has to interact with itself considerably more weakly than normal matter interacts with itself. So it can't be an exact mirror.johne1618 said:Ok - so if dark matter was mirror matter then in the early Universe it should have been a mirror ionized plasma in the same way that normal matter was an ionized plasma. Thus even if it didn't interact with normal matter at all it should still have interacted strongly with itself. We don't see evidence of that so dark matter is probably not mirror matter.
Thanks for the clarification.
Lensman said:This article appeared March 2nd on Science Daily. Quite interesting. Any comments?
http://www.sciencedaily.com/releases/2012/03/120302101413.htm
TrickyDicky said:The Bullet Cluster is claimed to provide the best evidence to date for the existence of dark matter (see for instance wikipedia entry). Is this new observation the best evidence to date against the existence of dark matter, then?
juanrga said:Nothing new, Dark Matter is the Vulcan planet of 21st century.
marcus said:amusing quip, but I don't think it's right. Density contour maps of DM clouds in many locations (e.g. around clusters of galaxies) have been made. The maps are interesting, show differences, show different things happening, and require explanation.
the hypothetical planet "Vulcan" was not something observed to be explained,
it was a KLUDGE explanation of precession in Mercury's orbit.
http://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet)
an unexplained peculiarity in Mercury's orbit was established as early as 1860, I think.
DM is also an essential feature of simulations of filamentary structure formation in early universe---and the simulations yield realistic-looking results.
DM is just too economical a way to explain this bunch of different things going on at widely different scales---galaxy, clusters of galaxies, filamentary structure.
The nature of DM is a major puzzle. It's not a one-time kludge like the hypothetical planet Vulcan.
Maybe you were kidding. Nice epigram
BTW I also think it's pretty clear that our present law of gravity, GR, is going to be MODIFIED. It is deficient in some recognized ways and people are working on that. So if you are trying to say GR has to be modified, you are "preaching to the converted". That, I think, is a different problem. Modifying, say in the course of developing a quantum theory of geometry and matter, is unlikely to supplant DM in all its different explanatory roles.
the people of the late 19th century, Vulcan was real. It was a planet. It had theoretical credibility and had actually been seen. Even textbooks accorded it a chapter.
Can you elaborate on the "continuous experimental failure of DM models"?juanrga said:I want to emphasize that continuous experimental failure of DM models (at galactic scale, clusters, cosmology...) and continuous null results in the dozens of experiments devoted to the search of dark matter would not be an impediment for true dark matter believers, who continue to believe that DM is real and will be found... Recall that Vulcan believers continued to search Vulcan even after was such hypothesis was discredited.
Chronos said:I was half expecting the MOND shoe to drop. That is the main 'contender' to supplant dark matter, although it fails even more spectacularly than DM.
...which is just plain incorrect. Cold dark matter fits all observations to date, and fits extremely well, with no special tuning required. The only objections to dark matter that are even close to valid are philosophical objections: some just don't like the idea of proposing a new type of matter.Drakkith said:I believe it claimed that current dark matter theory fails miserably itself.
Whitewolf4869 said:And the GODs have created a new kind of matter Amen!
Dark matter is an invisible and mysterious substance that makes up about 27% of the universe. Its core is defying explanation because it behaves differently than normal matter and emits no light, making it difficult to study and understand.
Scientists study dark matter through indirect observations, such as its gravitational effects on visible matter, and through computer simulations. They also use specialized instruments, such as the Large Hadron Collider, to try and detect dark matter particles directly.
Some theories suggest that dark matter is made up of exotic particles, such as WIMPs (Weakly Interacting Massive Particles) or axions. Other theories propose modifications to the laws of gravity to explain the observed effects of dark matter.
The core of dark matter is puzzling because it seems to be denser than expected, with a higher concentration of dark matter particles. This contradicts current theories and simulations, leading to a lack of understanding about the properties and behavior of dark matter.
The inability to explain the core of dark matter has significant implications for our understanding of the universe and its evolution. It also presents challenges for future research and the development of new theories to explain the mysteries of dark matter.