Good current paper on mass / luminosity and rotation curves
in [Physics]
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From: dlzc on 30 Jun 2010 21:13 Dear eric gisse: On Jun 30, 5:24 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: > dlzc wrote: > > On Jun 30, 12:04 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: > >> dlzc wrote: > >> >http://arxiv.org/abs/1005.3154 > > >> > Provides a lot of background into how Dark Matter > >> > is arrived at (as a free parameter, whose spatial > >> > distribution is far from simple, depending on the > >> > M/L modelled internal to the target galaxy). > > >> You do know that's not the only evidence for dark > >> matter, right? > > > Lest we go through your list of "evidence", what you > > have supplied to date can be done with simply normal > > matter. > > Not if you believe in electromagnetic theory. You require > some very special pleads to make bulk amounts of > hydrogen invisible, especially in *this* galaxy where radio > isn't redshifted into oblivion. "Heliosheath". Plenty of bulk hydrogen available, and invisible until it is braked. And we also (purportedly) are in a sparsely populated portion of the galaxy... > > If you have something > > other than rotation curves (which this paper says uses M/L) > > What the paper actually says is the following: > > We assume that the rotation curve V(R) of the disk > galaxy, for which we want to construct a mass model, > is known (i.e., it has been ?observed?); as a > mathematical boundary condition, we assume that the > rotation curve remains flat at V_\infty out to infinite > radii. They say a lot more than that. Like where they compare their results to an actual galaxy. > Rotation curves are direct observables. The interpretation > does depend on mass to luminosity ratios, which are ALSO > observables. It isn't as if what the paper does is controversial > to your position. It is the method used. Just as I told you. > You just have to explain how to fill in that rather substantial > amount of dark matter with normal matter while still playing > by the observed rules of electromagnetism and gravitation. Done. Even described in that paper. > > or gravitational lensing (which we both know matter alone > > can do, and highly ionized "sparse" normal matter is Dark > > for visible light and less energetic observations), I'd love to > > hear about it. > > Except normal matter isn't dark for the entire electromagnetic > spectrum. Just some of it. Like has already been discussed. Yep. We have to have a known x-ray source behind a region, in order to see it. Those are fairly rare. > > I expressed a desire to know "how it was done", and I > > found a paper that describes that. It neither agrees with > > me (even though it describes an M/L-based model that > > needs no Dark Matter except outside the visible disk), > > Uh, that doesn't mean as much as you think. It takes a lot > of matter to flatten out the rotation curves on the edge of a > galaxy. *And* we can in some cases see such normal matter. > > nor does it disagree with you. It just drops > > markers in the space I was interested in investigating. > > I thought *you* might be interested in knowing too. > > > As to Dark Matter: http://arxiv.org/abs/1005.4688 > > I wonder how you get "turbulence" with a strong Dark > > Matter component, neutrinos or not? > > No idea. I don't run the hydrocode simulations, or study > them in sufficient detail. Let me save you time. You cannot get turbulence without friction. You cannot get friction with Dark Matter, even neutrinos. David A. Smith
From: Yousuf Khan on 2 Jul 2010 03:27 On 7/1/2010 4:43 AM, dlzc wrote: > Dear eric gisse: > As to Dark Matter:http://arxiv.org/abs/1005.4688 > I wonder how you get "turbulence" with a strong Dark Matter component, > neutrinos or not? > > David A. Smith It would be pretty difficult to get turbulence in a "perfect fluid", as Eric likes to keep describing Dark Matter as. Yousuf Khan
From: Yousuf Khan on 2 Jul 2010 03:32 On 6/30/2010 11:52 PM, dlzc wrote: > http://arxiv.org/abs/1005.3154 > > Provides a lot of background into how Dark Matter is arrived at (as a > free parameter, whose spatial distribution is far from simple, > depending on the M/L modelled internal to the target galaxy). > > David A. Smith Here was another one, a bit more basic. [1006.2483] Dark Matter: A Primer http://arxiv.org/abs/1006.2483 Yousuf Khan
From: Androcles on 2 Jul 2010 04:47 "Yousuf Khan" <bbbl67(a)spammenot.yahoo.com> wrote in message news:VMmdnUahCLWGC7DRnZ2dnUVZ8sSdnZ2d(a)giganews.com... | On 6/30/2010 11:52 PM, dlzc wrote: | > http://arxiv.org/abs/1005.3154 | > | > Provides a lot of background into how Dark Matter is arrived at (as a | > free parameter, whose spatial distribution is far from simple, | > depending on the M/L modelled internal to the target galaxy). | > | > David A. Smith | | Here was another one, a bit more basic. | | [1006.2483] Dark Matter: A Primer | http://arxiv.org/abs/1006.2483 | | Yousuf Khan "In the early 1930s, J. H. Oort found that the motion of stars in the Milky Way hinted at the presence of far more galactic mass than anyone had previously predicted. By studying the Doppler shifts of stars moving near the galactic plane, Oort was able to calculate their velocities, and thus made the startling discovery that the stars should be moving quickly enough to escape the gravitational pull of the luminous mass in the galaxy. Oort postulated that there must be more mass present within the Milky Way to hold these stars in their observed orbits. However, Oort noted that another possible explanation was that 85% of the light from the galactic center was obscured by dust and intervening matter or that the velocity measurements for the stars in question were simply in error." The error is indeed simple. Had Oort used emission theory his dork matter would vanish. Thus dork matter is the reductio-ad-absurdum of the GR conjecture.
From: Sam Wormley on 2 Jul 2010 09:48
On 6/30/10 12:52 PM, dlzc wrote: > http://arxiv.org/abs/1005.3154 > > Provides a lot of background into how Dark Matter is arrived at (as a > free parameter, whose spatial distribution is far from simple, > depending on the M/L modelled internal to the target galaxy). > > David A. Smith David--The case for the existence of dark matter is strong. There is copious observational data showing way more gracvitational influencve than can be accounted for bu baryonic matter. Background: http://en.wikipedia.org/wiki/Dark_matter Quoting from Ned Wright's http://www.astro.ucla.edu/~wright/cosmology_faq.html#DM What is the dark matter? "When astronomers add up the masses and luminosities of the stars near the Sun, they find that there are about 3 solar masses for every 1 solar luminosity. When they measure the total mass of clusters of galaxies and compare that to the total luminosity of the clusters, they find about 300 solar masses for every solar luminosity. Evidently most of the mass in the Universe is dark. If the Universe has the critical density then there are about 1000 solar masses for every solar luminosity, so an even greater fraction of the Universe is dark matter. But the theory of Big Bang nucleosynthesis says that the density of ordinary matter (anything made from atoms) can be at most 10% of the critical density, so the majority of the Universe does not emit light, does not scatter light, does not absorb light, and is not even made out of atoms. It can only be "seen" by its gravitational effects. This "non-baryonic" dark matter can be neutrinos, if they have small masses instead of being massless, or it can be WIMPs (Weakly Interacting Massive Particles), or it could be primordial black holes. My nominee for the "least likely to be caught" award goes to hypothetical stable Planck mass remnants of primordial black holes that have evaporated due to Hawking radiation. The Hawking radiation from the not-yet evaporated primordial black holes may be detectable by future gamma ray telescopes, but the 20 microgram remnants would be very hard to detect". |