Good current paper on mass / luminosity and rotation curves
in [Physics]
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From: Yousuf Khan on 2 Jul 2010 17:01 On 7/3/2010 1:18 AM, eric gisse wrote: > Yousuf Khan wrote: >> It would be pretty difficult to get turbulence in a "perfect fluid", as >> Eric likes to keep describing Dark Matter as. > > Very good, at least one of you is learning. > > The only mechanism for turbulence or something close to it would be > gravitational friction in multibody interactions. > > That there have been no observations of clumpy dark matter with the specific > exception of cluster mergers should tell you somsething. That's a pretty *big* exception. The Earth is flat, except when you look at it from space. Yousuf Khan
From: eric gisse on 2 Jul 2010 20:49 Yousuf Khan wrote: > On 7/3/2010 1:18 AM, eric gisse wrote: >> Yousuf Khan wrote: >>> It would be pretty difficult to get turbulence in a "perfect fluid", as >>> Eric likes to keep describing Dark Matter as. >> >> Very good, at least one of you is learning. >> >> The only mechanism for turbulence or something close to it would be >> gravitational friction in multibody interactions. >> >> That there have been no observations of clumpy dark matter with the >> specific exception of cluster mergers should tell you somsething. > > That's a pretty *big* exception. The Earth is flat, except when you look > at it from space. Turbulence typically refers to self-interactions within a fluid. I'm pointing out the specific exception now rather than having to point out later and then deal with 'but you said there's no turbulence!!!!' response. Its' like people aren't listening when I say dark matter is modeled as a perfect fluid. What the hell do folks think that implies? > > Yousuf Khan
From: Yousuf Khan on 3 Jul 2010 01:41 On 7/3/2010 6:49 AM, eric gisse wrote: > Turbulence typically refers to self-interactions within a fluid. I'm > pointing out the specific exception now rather than having to point out > later and then deal with 'but you said there's no turbulence!!!!' response. > > Its' like people aren't listening when I say dark matter is modeled as a > perfect fluid. What the hell do folks think that implies? Then it's not a perfect fluid if there are self-interactions. You can say it's *close* enough to a perfect fluid at the galactic scale. At bigger scales, it is not. Second of all, you do realize that all of these "if...then...but if...else..." type behaviours of Dark Matter is exactly what Dark Fluid is supposed to address. Yousuf Khan
From: dlzc on 3 Jul 2010 14:54 On Jul 2, 8:48 am, Sam Wormley <sworml...(a)gmail.com> wrote: > On 6/30/10 12:52 PM,dlzcwrote: > > >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--The case for the existence of dark matter is > strong. There is copious observational data showing > way more gravitational influence than can be > accounted for by baryonic matter. Only by choice of M/L modelling, Sam. No theory requires DM. Only the choice of M/L models, gives us DM. > 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. .... depending on the M/L model choice. > 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. .... just like the missing normal mass between us and quasars... entirely Dark, except that it absorbs X-rays. > 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". We'd see them in the laboratory. David A. Smith
From: dlzc on 3 Jul 2010 15:24
Dear eric gisse: This topic is on topic in sci.astro. Leave it in the list of newsgroups. If you have the "nuts" to post on sci.astro, don't alter the Followup-to to remove it. On Jul 2, 2:17 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: > dlzc wrote: > > On Jun 30, 5:24 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: > >>dlzcwrote: > >> > On Jun 30, 12:04 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: > >> >>dlzcwrote: > >> >> >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". > > A region whose density is measured in atoms per > cubic meter, And yet is sufficient, given a choice of M/L model. > > Plenty of bulk hydrogen available, and invisible until > > it is braked. > > Unless you point a radio telescope at the 21cm line, > which neutral hydrogen radiates at. Or talk to an > astronomer about the general irritant which interstellar > hydrogen poses to observations at the galactic center. I'm refering to the ionized stuff, and you know that. > > 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. > > What completely baffles me is your stark > unwillingness to look at the generic features of the > expected rotation curves, and the observed rotation > curves. No actual discussion of how much mass is > there is required. Excuse me? I am refusing to look? And I don't understand that a rotation curve depends on mass to keep the system bound? > >> 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. > > Yeah, you don't like the method. There are a number of methods. They mentioned them. > Do you have an argument that isn't the scientific > equivalent of parents who think vaccines give kids > autism? Do you have an argument at all, even one that clearly states that you accept Dark Matter hook, line, and sinker, even though no cosmology provides for production of the entirely invisible? Even though we have detected normal matter that we cannot observe without an X-ray source behind it? Sure, you are in a fine camp. Lots of people accept that M/L based on experimentally indistinguishable choices, can eliminate or increase the amount of Dark Matter required. > >> 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. > > Except in, once again, the bullet cluster which is lit up like > a goddamn Roetgen christmas tree. Dark matter remains dark. The "tree" is in the center. You've already acknowledged we can neither see the Dark Matter, nor the stars in those two galaxies... on either side of it. So there is nothing to support either case in the Bullet Cluster. > >> > 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. > > Really, enough normal matter to completely remove the > need for dark matter? How do you know there isn't? The "missing normal matter" was much greater than the amount of normal matter we could identify at one time. > >> > 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. > > Just a thought, but perhaps you could read the paper > instead of guessing? The turbulence specifically refers > to the behavior of normal matter. Yes, thank you. See above where I said "cannot have a strong Dark Matter component"? Turbulence = friction = normal matter David A. Smith |