Good current paper on mass / luminosity and rotation curves
in [Physics]
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From: eric gisse on 2 Jul 2010 12:51 Sam Wormley wrote: [...] Put down the copy and paste for a minute. David seems to think that dark matter doesn't exist because the jump between galactic luminosity and stellar rotation curves is 'faulty' and that dark matter can be, in fact, replaced by fully ionized hydrogen. Or neutral hydrogen. The answer seems to change frequently so I'm not sure which. If you are going to paste him stuff, paste him stuff out of an electromagnetism textbook so he can catch up with what the rest of science figured out a century ago.
From: Sam Wormley on 2 Jul 2010 13:08 On 7/2/10 11:51 AM, eric gisse wrote: > Sam Wormley wrote: > > [...] > > Put down the copy and paste for a minute. > > David seems to think that dark matter doesn't exist because the jump between > galactic luminosity and stellar rotation curves is 'faulty' and that dark > matter can be, in fact, replaced by fully ionized hydrogen. Or neutral > hydrogen. The answer seems to change frequently so I'm not sure which. > > If you are going to paste him stuff, paste him stuff out of an > electromagnetism textbook so he can catch up with what the rest of science > figured out a century ago. Duh, neutral hydrogen and fully ionized have unique spectra. Whereas dark matter does not interact electromagnetically or very weakly. Most researches think that dark matter likely interacts like neutrinos, mediated by the weak interaction.
From: eric gisse on 2 Jul 2010 15:17 dlzc wrote: > 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". A region whose density is measured in atoms per cubic meter, > 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. > 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. > >> 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. Do you have an argument that isn't the scientific equivalent of parents who think vaccines give kids autism? > >> 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. > >> > 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? > >> > 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. > > David A. Smith
From: eric gisse on 2 Jul 2010 15:18 Yousuf Khan wrote: > 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. 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. > > Yousuf Khan
From: eric gisse on 2 Jul 2010 16:01
Sam Wormley wrote: > On 7/2/10 11:51 AM, eric gisse wrote: >> Sam Wormley wrote: >> >> [...] >> >> Put down the copy and paste for a minute. >> >> David seems to think that dark matter doesn't exist because the jump >> between galactic luminosity and stellar rotation curves is 'faulty' and >> that dark matter can be, in fact, replaced by fully ionized hydrogen. Or >> neutral hydrogen. The answer seems to change frequently so I'm not sure >> which. >> >> If you are going to paste him stuff, paste him stuff out of an >> electromagnetism textbook so he can catch up with what the rest of >> science figured out a century ago. > > > Duh, neutral hydrogen and fully ionized have unique spectra. Correct. Now let's see how long it takes for David to figure this out. > Whereas dark matter does not interact electromagnetically or > very weakly. Most researches think that dark matter likely > interacts like neutrinos, mediated by the weak interaction. |