Good current paper on mass / luminosity and rotation curves
in [Physics]
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From: dlzc on 4 Jul 2010 14:28 Dear Yousuf Khan: On Jul 4, 4:49 am, Yousuf Khan <bbb...(a)spammenot.yahoo.com> wrote: > On 7/4/2010 1:24 AM,dlzcwrote: > > > 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. > > Just to play devil's advocate for a moment, Good. > but if there's so much matter that only can be seen > through X-ray absorption, 1 atom per cc in the Milky Way is known. I figure this comes out to 0.3 solar masses per cubic light year. > then why aren't we seeing it within our own galaxy, > where there should be plenty of X-ray sources > lighting up the sky, at least from within the galactic > disk? We know this normal mass is here. We cannot see variations in these x- ray sources along the galactic plane, in much the same way we did not "know" the ozone layer blocked UV from stars, until the ozone hole allowed UV spectral lines to be detected. The M/L assumption assumes the "average stars" in all areas of the disk: - are the same size / volume, - same temperature / age, - are "amplified" by the same amount of attendant dust (scatters light from nearby stars), and - are accompanied by the same amount of "unbelievably ionized" normal matter per unit area (rather than volume). If it is diffuse, there needn't be viscosity to speak of, just interfaces defined by stellarsheaths. David A. Smith
From: John Park on 4 Jul 2010 15:10 dlzc (dlzc1(a)cox.net) writes: > Dear eric gisse; [...]> >> >> > On Jul 2, 2:17 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: >> >>dlzcwrote: >> >> > 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. >> >> Pretend the galaxy is a sphere that's 125,000 light years wide. >> >> Estimates of the dark matter bulge are comfortably nestled >> in the region of 2x10^12 solar masses, while in comparison >> the mass of what's directly observable is in the region of >> 10^10 solar masses. > > What is*directly* observable is 'an" order of magnitude less than > this. That is the "sin" committed by M/L. We accept that there is > 'some' normal matter that we cannot see. And we assume that ratio is > the same across the galaxy. > >> 125,000 light years is ~10^21 m. The volume for that sphere >> is ~2x10^63 m^3. >> 2x10^12 solar masses =3D 4x10^42 kg >> 1 kg of hydrogen =3D 1000 moles =3D 6x10^26 atoms >> >> so 2x10^12 solar masses ~ 10^69 atoms >> >> That many atoms of hydrogen in that 125,000 light year sphere >> would require an _average_ density of about 10^6 atoms/m^3 >> which is an order of magnitude or 6 higher than the average >> density of vacuum. > > Not in the Milky Way. We average nearly 1 particle per cc, or 10^6 > particles per m^3. > >> Which is, in turn, a massive underestimate because I assumed >> the galaxy was a sphere. > > Dark Matter is roughly allocated as an oblate sphere, if Andromeda is > any guide. > >> Add another factor of 15 or so if you want a number closer >> to reality. >> >> IT CAN NOT WORK. DO YOU SEE YET? You can DOUBLE >> the effective size of the galaxy and you will still be orders of >> magnitude off. > > Actually, no. Your own numbers indicate that the interstellar gases > alone could do it. > >> >> > 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. >> >> Except the traversal of electromagnetic waves through a >> plasma leaves rather significant tell tale signs. The drift >> velocity of bulk anything about a galaxy will induce >> massive faraday rotation in electromagnetic waves, >> because you demand a wholly ionized plasma of a >> significant amount of hydrogen. > > Doesn't work unless you have recombination. Once hydrogen loses the > one electron... > >> That we don't see such polarization in the CMB, or >> evidence of Compton scattering off all those bulk >> electrons that are required, is rather telling. > > No, its not at all telling. > >> And review basic electromagnetic theory. You are >> essentially demanding that 10^12 solar masses >> worth of separated charge - where's the energy coming >> from to maintain that separation? > > At tens of millions of degrees, its no problem. You know its there. > You yourself have cited the values. > >> Hmm, how much energy would that be? Hydrogen's >> binding energy is 13.6 eV, so you'll need 6x10^26 * >> 13.6eV =3D 8x10^27 eV worth of energy expended to do >> that. Any guesses as to where that energy is coming >> from, and how frequently it needed to be expended? > > None at all, if it never recombines. And it is still zipping along > from the supernova or Big Bang that launchd it. > >> >> > 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 =A0which we want to construct a >> >> >> =A0 =A0 =A0 =A0 mass model, is known (i.e., it has =A0been >> >> >> =A0 =A0 =A0 =A0 ?observed?); as a mathematical boundary >> >> >> =A0 =A0 =A0 =A0 condition, we assume that the rotation >> >> >> =A0 =A0 =A0 =A0 curve remains flat at V_\infty out to infinite >> >> >> =A0 =A0 =A0 =A0 radii. >> >> >> > They say a lot more than that. =A0Like 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? =A0I am refusing to look? =A0And 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. =A0Just as I told you. >> >> >> Yeah, you don't like the method. >> >> > There are a number of methods. =A0They 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? >> >> Cosmology doesn't have a means to produce the baryons >> that build what we see, either. The prevalence of matter >> over antimatter is an unsolved problem. >> >> Try to keep that in mind. > > Try and explain how neutrinos that are produced with high energies, > get cooled enough to be gravitationally captured. > >> > Even though we >> > have detected normal matter that we cannot observe without >> > an X-ray source behind it? >> >> Hardly a strong argument. What you propose would scream in >> the EM like a goddamn nuke going off at night. > > But it doesn't. The density isn't high enough. > >> There is no possible way we could not see it. > > We can't. We don't. We can only see these huge volumes of mass, > because the oxygen is missing five electrons. > >> > Sure, you are in a fine camp. =A0Lots of people accept that >> > M/L based on experimentally indistinguishable choices, can >> > eliminate or increase the amount of Dark Matter required. >> >> Except you are wrong. > > It is in the paper cited, and it was reporting other's papers. > >> There is flexibility in what is required as the answer is model >> dependent, but the rotation curves have to be replicated. Which >> basic Newtonian theory will tell you requires a lot of matter where >> none is seen. You require dark matter whether you realize it or >> not, the only question is 'how much?'. > > No, *I* don't require *any* Dark Matter. > >> This is why I know you haven't looked at the rotation curves and >> seriously thought about what you are seeing. > > I have. M/L makes your imaginary mistake for 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. =A0Even described in that paper. >> >> >> >> > or =A0gravitational 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. =A0Just some of it. Like has already been discussed. >> >> >> > Yep. =A0We have to have a known x-ray source behind a region, >> >> > in order to see it. =A0Those 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. =A0You've already acknowledged we can >> > neither see the Dark Matter, nor the stars in those two galaxies... on >> > either side of it. >> >> Uh...this again? Just because a star is far away does not mean it is >> invisible, just that it is a point source. All those point sources blurre= > d >> together form what we see, in addition to scattering off dust. > > The dust was left behind. No blur. Give up on the Bullet Cluster. > >> > So there is nothing to support either case in the Bullet Cluster. >> >> Are you being deliberately retarded? > > Stick it in your ear. > > *plonk* > Since you've plonked Eric, I'll tackle this. According to the Wikipedia article on the interstellar medium, ionised hydrogen can be detected at levels appreciably less than 1 particle per cc by the H-alpha radiation it emits (from recombinations) and by its dispersive effect of on pulsar signals. At the levels in question ionised hydrogen is not "dark". Moreover, from the same article, such a plasma has a scale height of about 1 kpc, so it doesn't look like a good candidate to explain rotation curves. --John Park
From: eric gisse on 4 Jul 2010 18:28 John Park wrote: [...] > Since you've plonked Eric, I'll tackle this. According to the Wikipedia > article on the interstellar medium, ionised hydrogen can be detected at > levels appreciably less than 1 particle per cc by the H-alpha radiation it > emits (from recombinations) and by its dispersive effect of on pulsar > signals. At the levels in question ionised hydrogen is not "dark". > > Moreover, from the same article, such a plasma has a scale height of about > 1 kpc, so it doesn't look like a good candidate to explain rotation > curves. > > --John Park Now watch the special pleads roll in for why the litany of effects this would have are not seen.
From: Yousuf Khan on 5 Jul 2010 05:32 On 7/5/2010 12:28 AM, dlzc wrote: > Dear Yousuf Khan: > > On Jul 4, 4:49 am, Yousuf Khan<bbb...(a)spammenot.yahoo.com> wrote: >> On 7/4/2010 1:24 AM,dlzcwrote: >> >>> 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. >> >> Just to play devil's advocate for a moment, > > Good. > >> but if there's so much matter that only can be seen >> through X-ray absorption, > > 1 atom per cc in the Milky Way is known. I figure this comes out to > 0.3 solar masses per cubic light year. Well, the 1 atom/cc average probably includes the mass of stars and their orbiting stellar systems. So by the law of averages, in areas of vacuum, the average density is probably less. The 0.3 solar mass/cly sounds an awful lot like the density of the surrounding neighbourhood of the Sun: the Sun is the only star for 4 light years, so dividing the mass of the Sun around this volume would likely result in 0.3 solar masses per cubic light year. >> then why aren't we seeing it within our own galaxy, >> where there should be plenty of X-ray sources >> lighting up the sky, at least from within the galactic >> disk? > > We know this normal mass is here. We cannot see variations in these x- > ray sources along the galactic plane, in much the same way we did not > "know" the ozone layer blocked UV from stars, until the ozone hole > allowed UV spectral lines to be detected. We didn't know the ozone was blocking UV beforehand? I find that hard to believe. The ozone layer scare was only in the early 80's/late 70's, so we learned about this connection so recently? > The M/L assumption assumes the "average stars" in all areas of the > disk: > - are the same size / volume, > - same temperature / age, > - are "amplified" by the same amount of attendant dust (scatters light > from nearby stars), and > - are accompanied by the same amount of "unbelievably ionized" normal > matter per unit area (rather than volume). If it is diffuse, there > needn't be viscosity to speak of, just interfaces defined by > stellarsheaths. I'm not getting what you're trying to say about ionized matter (regardless of whether it is "unbelievably" ionized or not). What's the ionized matter supposed to represent? And why is it ionized? Also not getting what the difference is whether they are assuming it over a unit area or a unit volume. What difference would that make? Yousuf Khan
From: dlzc on 5 Jul 2010 23:30
Dear John Park: On Jul 4, 12:10 pm, af...(a)FreeNet.Carleton.CA (John Park) wrote: .... > Since you've plonked Eric, I'll tackle this. Eric needs to (be able to) go back to school. He is making everyone miserable until he can. If there were anything I could do... > According > to the Wikipedia article on the interstellar medium, > ionised hydrogen can be detected at levels appreciably > less than 1 particle per cc by the H-alpha radiation it > emits (from recombinations) It is known to be that density (average, Milky Way). It is known not all to be recombined, and therefore somewhat transparent, somewhat Dark (for visible and longer wavelengths). Yet when we look along the galactic plane, we have to resort to IR, to be able to see very far. > and by its dispersive effect of on pulsar signals. > At the levels in question ionised hydrogen is not > "dark". It is intergalactically, Dark. At least to wavelengths visible and below. > Moreover, from the same article, such a plasma has > a scale height of about 1 kpc, so it doesn't look like a > good candidate to explain rotation curves. Mass, normal mass, is all that is required. Not sure what you mean by "scale height"? Andromeda (a spiral galaxy I'd prefer to use for discussions of Dark Matter, because it is spiral (not barred, or perhaps two recently merged galaxies like the Milky Way), typical, and close enough to accurately measure things... it Dark Matter stops about 60% above and below the galactic plane... My bigger concern, is what does a much larger amount of normal mass do to the rest of BB cosmology. That the matching amount of antimatter is still missing is no bigger problem than it was before. Because we'd be missing anti-Dark matter too... David A. Smith |