|
|
Thread Tools | Display Modes |
#81
|
|||
|
|||
Hubble makes 3D dark matter map
Kent Paul Dolan wrote:
Richard Saam wrote: If such were the case, these objects surely would not be observable from earth yet provide observed gravitational lensing character. Well, an interesting extension to your calculation would be, how often would the disk of earth, considered as a flyswatter, encounter an object at each size scale, as earth sweeps through space both in orbit around the sun and moving through the galaxy with the solar system. Now, is that in agreement with what is actually seen impacting the earth or its atmosphere, in the "quiet times" between major meteor showers with known local-to-this-solar-system causes? In other words, we can't see those objects in the Bullet galaxy, but if they are "the dark matter in general", should we be able to observe them if they have that same needed density for lensing, close to home, as would be expected? If so, do we? FWIW xanthian. An interesting question. Are such residual objects of sufficient size that they can be observed locally?? The only way I know how to approach the fly swatter concept is in terms of the mean free path concept which has its roots back in the early 20th century with Miron Smoluchowski and others addressing particle collision data for particles assuming other fields (electromagnetic, gravitational etc.) contributing insignificantly. mean free path = 1/(sqrt(2)*pi*N*d^2) where N = 1 object/ rd^3 and object diameter (d) = rb Extending previous calculations, it appears plausible that there could be asteroid like objects with a size on the order of 1 kilometer (1E5 cm) and 9E7 kilometers (9E+12 cm) from each other with mean free path of 2E10 light years (very few collisions) dispersed in such a manner to form a stable lens with density 1.213E-24 g/cc and these asteroid like objects not observable locally(interstellar medium) or distantly(bullet cluster medium) with insignificantly rare earth or even solar impacts. As for collision of multiple sized objects(i & j), Smoluchowski addressed that as: collision rate/volume/time ~ Ni*Nj*(di+dj)^3 / time perhaps someone can do the calculation but it does not appear that stellar(i)-object(j) collisions would significantly disrupt (swat) this stable lens. space space object object object mean rd rd rb mass solar free (cm) (lt yr)(cm) (g) masses path (lt yr) 9E-01 1E-18 1E-08 1E-24 5E-58 2E-03 ~hydrogen 9E+00 1E-17 1E-07 1E-21 5E-55 2E-02 ~molecules 9E+01 1E-16 1E-06 1E-18 5E-52 2E-01 9E+02 1E-15 1E-05 1E-15 5E-49 2E+00 9E+03 1E-14 1E-04 1E-12 5E-46 2E+01 9E+04 1E-13 1E-03 1E-09 5E-43 2E+02 9E+05 1E-12 1E-02 1E-06 5E-40 2E+03 9E+06 1E-11 1E-01 1E-03 5E-37 2E+04 ~dust 9E+07 1E-10 1E+00 1E+00 5E-34 2E+05 ~dust 9E+08 1E-09 1E+01 1E+03 5E-31 2E+06 ~asteroid 9E+09 1E-08 1E+02 1E+06 5E-28 2E+07 ~asteroid 9E+10 1E-07 1E+03 1E+09 5E-25 2E+08 ~asteroid 9E+11 1E-06 1E+04 1E+12 5E-22 2E+09 ~asteroid 9E+12 1E-05 1E+05 1E+15 5E-19 2E+10 ~asteroid 9E+13 1E-04 1E+06 1E+18 5E-16 2E+11 9E+14 1E-03 1E+07 1E+21 5E-13 2E+12 9E+15 1E-02 1E+08 1E+24 5E-10 2E+13 9E+16 1E-01 1E+09 1E+27 5E-07 2E+14 ~earth 9E+17 1E+00 1E+10 1E+30 5E-04 2E+15 9E+18 1E+01 1E+11 1E+33 5E-01 2E+16 ~sun 9E+19 1E+02 1E+12 1E+36 5E+02 2E+17 9E+20 1E+03 1E+13 1E+39 5E+05 2E+18 9E+21 1E+04 1E+14 1E+42 5E+08 2E+19 9E+22 1E+05 1E+15 1E+45 5E+11 2E+20 ~Milky Way 9E+23 1E+06 1E+16 1E+48 5E+14 2E+21 9E+24 1E+07 1E+17 1E+51 5E+17 2E+22 |
#82
|
|||
|
|||
Hubble makes 3D dark matter map
|
#83
|
|||
|
|||
Hubble makes 3D dark matter map
In article ,
Richard Saam wrote: The situation is a little different in the understood universe where the critial matter 'Mc' in arbitrary volume 'Vc' with critical density (~10^-30 g/cc) 'rhoc' is greater than baryonic matter 'Mb' but does not displace the baryonic matter 'Mb' in its volume 'Vb' with density(~10^-24 g/cc) 'rhob' but permeates it where Vc Vb and Vb included in Vc. Mc = rhoc*Vc Mb = rhob*Vb Mc Mb and rhoc*Vc rhob*Vb therefo rhoc/rhob Vb/Vc and rhoc (Vb/Vc)*rhob so the critical mass (Mc) is greater than baryonic mass (Mb) and the critical density (rhoc) is less than baryonic density (rhob) if arbitrary volume Vc Vb. Vc could typically have dimensions of (intergalactic distance)^3 and Vb could typically have dimensions of (galactic diameter)^3 I'm sorry, but I can't make any sense of this. I promise you that when people compare the densities of baryonic matter and dark matter, they're doing a fair comparison -- that is, they're comparing the mass of all the baryons in some (suitably large) volume to the mass of dark matter in the same volume. The densities involved are average densities over large volumes: in some small regions (such as, say, the interior of the Earth) the density of dark matter is much less than the baryon density. -Ted -- [E-mail me at , as opposed to .] |
#85
|
|||
|
|||
Hubble makes 3D dark matter map
"Kent Paul Dolan" wrote:
Hans Aberg wrote: One idea that comes to my mind is that very young, nearby galaxies are very hard to observe for two reasons: they are faint, and quickly gets absorbed into larger galaxies. Why would any even exist? Surely after ~14 billion years, most of the easily accumulated intergalactic gas has long ago gathered into galaxies, and the remaining cases gathering more recently would be so thinly scattered throughout the universe that the chance of even one being "nearby" for useful meanings of that vague term would be "slender to none"? By the way, the article I URLed yesterday from Scientific American: http://www.sciam.com/article.cfm?cha...CA562C33C4F03C [yes, I know that's not a refereed paper] describes in part that dark energy expansion has indeed slowed galaxy generation to a crawl, "The central piece of evidence is the rough coincidence in timing between the end of most galaxy and cluster formation and the onset of the domination of dark energy. Both happened when the universe was about half its present age." slowed inflow of star-generation gases from the intergalactic regions into large galaxies to a non-issue, so probably all we have in dispute is what "nearby young" means. "The inexorable shift in the balance between the two" [dark energy and gravity] "eventually caused the expansion rate to switch from deceleration to acceleration. The structures in which galaxies reside were then pulled apart, with a gradual decrease in the galaxy merger rate as a result. Likewise, intergalactic gas was less able to fall into galaxies. Deprived of fuel, black holes became more quiescent." xanthian. Also, it says we (the Local Group) aren't ever going to reach the Virgo supercluster, because the dark energy expansion is outrunning gravity's collapsing effect at that distance, a factoid that is going to make it lots easier for _me_ to sleep at night, boy howdy. "An example of how dark energy alters the history of galaxy clusters is the fate of the galaxies in our immediate vicinity, known as the Local Group. Just a few years ago astronomers thought that the Milky Way and Andromeda, its closest large neighbor, along with their retinue of satellites, would fall into the nearby Virgo cluster. But it now appears that we shall escape that fate and never become part of a large cluster of galaxies. Dark energy will cause the distance between us and Virgo to expand faster than the Local Group can cross it." |
#86
|
|||
|
|||
Hubble makes 3D dark matter map
"re" == rloldershaw@amherst edu writes:
re On Feb 10, 2:02 pm, Joseph Lazio wrote: The interested reader is referred to Schee (2006). Other examples of such papers can easily be found by perusing the Astronomical Data System or astro-ph. re Millions of dollars and countless man-hours of effort have been re expended in this effort to find hypothetical "WIMPS", CDM, sterile re neutrinos, axions, etc. A vast literature on the subject exists. re So far not one single shread of evidence for their existence has re appeared. This from the person constantly exhorting us to keep an open mind. Given the forum, your argument seems far more rhetorical than scientific. A small project involving only 20 people working for a year could easily consume "millions of dollars" and "20 man-years of effort." A more persuasive approach would be to compare the expected density of such particles with the current experimental limits. How do they compare? What is required to produce even more stringent limits? What's the acceptable risk-return balance? (In other words, we should tolerate some high-risk, high-payoff experiments, ones that might be wrong, but, if successful, would be incredibly important.) -- Lt. Lazio, HTML police | e-mail: No means no, stop rape. | http://patriot.net/%7Ejlazio/ sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html |
#87
|
|||
|
|||
Hubble makes 3D dark matter map
"Joseph Lazio" schreef in bericht
... "HA" == Hans Aberg writes: I think somebody (Ted, Phillip?) has already discussed this. Briefly, we have estimates for the density of baryonic matter and the total density of matter in the Universe. HA What might be pitfalls of those estimates is if they build on some HA untested theory about formation from the Big Bang. I think the methods of estimating both the density of baryonic matter and the total density of matter have been discussed at length in this newsgroup, as well as in various review papers that one could find on astro-ph (for example). [...] There needs to be some non-baryonic dark matter. Indeed, we already know of one kind of non-baryonic dark matter, neutrinos. They are not baryons, they have mass, and they do not interact via the electromagnetic force (...). If we know of one kind of non-baryonic dark matter, it is not too difficult to think that there might be other kinds. HA I think that explaining dark matter as mainly composed of HA neutrinos has been ruled out. My point was not to claim that neutrinos explain dark matter. My point is that neutrinos are a form of dark matter. I think the onus is actually more on those who claim that there is no dark matter. We know of one example already (neutrinos). How can one be so certain that there are no other kinds of dark matter particles? The onus is for the people who claim that there is dark matter to demonstrate why such a solution is required Our solar system consists of planets and the kuiper belt Outside our solar system is the Oort Cloud to explain comets. Both the kuiper belt and the Oort Cloud are filled with visible matter. The onus is for the people who claim that there is dark matter to demonstrate why in our galaxy the disc can not be filled like the kuiper belt with Oort Cloud type objects to explain flat galaxy rotation curves. See also sci.astro "Dark matter hides, physicists seek (Forwarded)" http://groups.google.be/group/sci.sp...c1 f587a2fdf4 Nicolaas Vroom http://users.pandora.be/nicvroom/ |
#88
|
|||
|
|||
Hubble makes 3D dark matter map
"Nicolaas Vroom" schreef in bericht
... I think the onus is actually more on those who claim that there is no dark matter. We know of one example already (neutrinos). How can one be so certain that there are no other kinds of dark matter particles? The onus is for the people who claim that there is dark matter to demonstrate why such a solution is required Our solar system consists of planets and the kuiper belt Outside our solar system is the Oort Cloud to explain comets. Both the kuiper belt and the Oort Cloud are filled with visible matter. The onus is for the people who claim that there is dark matter to demonstrate why in our galaxy the disc can not be filled like the kuiper belt with Oort Cloud type objects to explain flat galaxy rotation curves. See also sci.astro "Dark matter hides, physicists seek (Forwarded)" http://groups.google.be/group/sci.sp...c1 f587a2fdf4 The sci.astro link is: http://groups.google.be/group/sci.as...d29e03d1907fe4 Nicolaas Vroom http://users.pandora.be/nicvroom/ |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Hubble tracks down a galaxy cluster's dark matter (Forwarded) | Andrew Yee | Astronomy Misc | 0 | July 17th 03 01:42 PM |