Good current paper on mass / luminosity and rotation curves
in [Physics]
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From: dlzc on 5 Jul 2010 23:43 Dear Yousuf Khan: On Jul 5, 2:32 am, Yousuf Khan <bbb...(a)yahoo.com> wrote: > On 7/5/2010 12:28 AM,dlzcwrote: > > 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. No. It is inferred from various measurements, and is *just* the gas / dust between the stars, or average, for the Milky Way. > 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. No, this is actually the interstellar density, in addition to the Sun. > >> 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? Some people knew ozone absorbed UV. But it surprised scientists that stars "developed" UV spectra on film through the ozone hole. http://www.theozonehole.com/fact.htm .... talks about what was known and suddenly realized. > > 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? Emissions form stars, supernovae, and remnants of the Big Bang. > And why is it ionized? I cannot answer a "why" question, but I have seen estimates that the intergalactic medium is the equivalent of some tens of millions of degrees. It is ionized (still in large part), perhaps because the intergalactic medium is so 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? Visible or luminous matter is confined to a thin disk, that gets thinner with increasing r. Yet "Dark Matter" is semispherical or torus shaped, if Andromeda is a good guide. The difference is the average density required... David A. Smith
From: John Park on 6 Jul 2010 13:42 dlzc (dlzc1(a)cox.net) writes: > Dear John Park: > > On Jul 4, 12:10=A0pm, 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... Speak for yourself. You are not everyone. I'll defer to Steve Willner's post for the substantive matters. --John Park
From: dlzc on 6 Jul 2010 14:41 Dear John Park: On Jul 6, 10:42 am, af...(a)FreeNet.Carleton.CA (John Park) wrote: > dlzc(dl...(a)cox.net) writes: > > Dear John Park: > > > On Jul 4, 12:10=A0pm, 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... > > Speak for yourself. You are not everyone. I'll defer to > Steve Willner's post for the substantive matters. Thanks for pointing that out. David A. Smith
From: dlzc on 6 Jul 2010 14:44 Dear Yousuf Khan: On Jul 5, 2:32 am, Yousuf Khan <bbb...(a)yahoo.com> wrote: > On 7/5/2010 12:28 AM,dlzcwrote: .... > >> 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. I was off by a factor of about 1000. It is more like 1/1000th of the mass of our Sun per cubic light year, at least near the galactic plane. David A. Smith
From: John Park on 9 Jul 2010 13:13
dlzc (dlzc1(a)cox.net) writes: > Dear Steve Willner: > > On Jul 8, 3:58=A0pm, will...(a)cfa.harvard.edu (Steve Willner) wrote: >> In article <503f477a-1472-4660-a7e7-c33085513...(a)y32g2000prc.googlegroups= > .com>, >> >> =A0dlzc<dl...(a)cox.net> writes: >> > I've seen what the mass distribution needs to be >> > for Andromeda, will that do? >> >> > -8- spin it around the "-", and orient them along the >> > axis of rotation of the spiral galaxy. =A0Not a torus, >> > obviously. >> >> What's your source for this? > > Andromeda shows DM up to about 60%r, above and below the galactic > plane. > >> I'm still not clear exactly what distribution you are >> suggesting, but to the extent I understand it (perhaps >> not at all), it looks grossly unstable both gravitationally >> and to its own pressure (given the temperature you >> suggest below). > > I don't see how it is gravitationally unstable, since it need have > essentially no friction. A sea of positive and negative charges > produce no viscosity. And as to temperature, we know temperatures > from ionization of moniority members... not so much from the "kinetic > theory of gasses". Have you tried to estimate a collision frequency for your plasma? For a density of 1 particle per cc and a temperature of 25 x10^6 K I get that an "electromagnetically significant collIsion" (i.e. an approach to within a distance comparable to the diameter of a hydrogen atom--so one could expect bremstrahlen or recombination) would happen something like once per week per particle. Such a plasma isn't going to last more than a few decades, let alone the age of the galaxy. And what about the loss of energy as synchrotron radiation in the galactic magnetic field? (I suspect a time-scale of a few years again, but from a very crude estimate.) --John Park |