Dark Matter Properties!

[qibbish]

Sorry if this has already made the rounds here - I'm relatively new. Recently, a handful of Cambridge physicist completed a survay of dwarf galaxy movements through a portion of the Milky Way. The upshot of this study has been to peg some solid numbers to this elusive stuff we call dark matter. <br /><br />Here is a reprint of the story by the UK Telegraph. This appears so recent that most detailed science oriented sites have yet to begin discussing it (and the team in question has yet to submit their paper to an Astrophysical journal).<br /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p><br /> Triumph of mind over dark matter<br />(Filed: 07/02/2006)<br /><br />It makes up nearly a quarter of the Universe, holds our galaxy in place, but cannot be seen.<br /><br />Dark matter has evaded all attempts to detect and illuminate it in the 73 years since its existence was first hypothesized.<br /><br />Now British astronomers have moved an important step closer to lifting the veil on the elusive material that has mystified generations of scientists, by calculating some of its basic physical properties for the first time.<br /><br />Prof Gerry Gilmore, of the Institute of Astronomy at the University of Cambridge, and colleagues used the world's most advanced optical telescope system to observe 12 dwarf galaxies around the edge of our own galaxy, the Milky Way.<br /><br />By studying the movement and mass of stars within these galaxies, they were able to calculate the minimum density and distribution of the dark matter around them.<br /><br />Their findings, expected to be published in a scientific journal soon, add substantially to what is known about the material that provides the cosmic glue that, through its gravitational force, keeps stars in their positions within galaxies.<br /><br />Prof Gilmore said: "This is the first time we have determined the property of dark matter robustly in a way that we expect will give us some real clues as to what the real physics of</p></blockquote>

 

[harmonicaman]

Hi <b>Qibbish;</b> welcome aboard!<br /><br />Yeah, we've batted this around and there's no firm consensus of opinion in here. <br /><br />Before cosmologists can make an accurate determination of how much "Exotic" Dark Matter is in the universe, they really need to first get an accurate measurement of how much "Regular" Dark Matter is out there -- like stellar black holes, brown dwarfs, dust, and all the other normal cosmic debris.<br /><br />I don't think we've accounted for all the regular matter yet, so it may be a bit premature to start blaming everything on something exotic, (violates Occams Razor). <br /><br />When we know exactly how much normal matter is in the universe, then by a simple process of elimination, we can accurately determine how much of it must be this exotic stuff.<br /><br />I'm having a hard time accepting the Exotic DM theories and in my opinion these observations are SWAG...

 

[mikeemmert]

Thanks for posting, Qibbish.<br /><br />There was an earlier article about the characterization of dark matter on Space.com, about a month ago, where gravitational lensing was used to map out some dark matter in a galaxy cluster. I thought that was on the STscI site, but there was a bunch of other really interesting stuff there:<br />about brown dwarfs , missing hydrogen , gravitational lenses, and more.<br /><br />Although I would agree that the search for "normal" dark matter should continue, I think we are getting enough of a picture of it to say for sure that "exotic" dark matter exists and that it must be something that is not baryonic and is not leptons or neutrinos.

 

[mikeemmert]

I know other stuff has been posted here about the observations you're reporting. And I know your's is new information because I had to calculate the dark matter's density myself. I got a result similar to what you have posted, so we'll go with what you posted.<br /><br />This stuff is actually like what my completely unscientific wild guess was like! Huge, rarified particles with extremely low density. Really strange.<br /><br />As far as the stuff not radiating, that's not surprising at all in view of the fact that whatever it is, it's transparent. Absorption and radiation of photons are the inverses of each other. At any given wavelength, a body will radiate the same percentage of radiation that it absorbs and will not radiate at any wavelenth at which radiation is either reflected or is transparent to. No substance is perfectly reflective or transparent, so there's always a little radiation, but this stuff apparently <i>is</i> perfectly transparent, so it won't radiate.<br /><br />If this stuff does interact with photons, I imagine it would be at very long radio wavelenths, which don't make it past our heliosphere.<br /><br />This is a pretty interesting subject.