Good current paper on mass / luminosity and rotation curves
in [Physics]
|
From: eric gisse on 12 Jul 2010 13:26 dlzc wrote: > On Jul 10, 3:45 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: >> dlzc wrote: >> >> [...] >> >> >> >> > The intergalactic and interstellar materials are known >> > (by the heavier elements) to be *ionized* to that >> > temperature, not "moving at that speed". >> >> Learning what temperature means would be abundantly >> helpful here. >> >> [...] > > http://arxiv.org/abs/1005.1085 > http://arxiv.org/abs/0911.2192 > http://arxiv.org/abs/0712.0476 > > Hard to believe one could have gravitationally bound matter, that was > moving in excess of escape speed. So yes, Eric, again you do need to > know a bit more about temperature, and that the "kinetic theory of > gases" is not the only way to do that. *If* it is so bound. > > I've already said they measured the temperature by the first > ionization, the first absorption band, of one of the minority > constituents. If you feel this is invalid... Steve Wilner had just addressed this. > > David A. Smith
From: dlzc on 13 Jul 2010 10:25 Dear Y.Porat: On Jul 11, 8:14 pm, "Y.Porat" <y.y.po...(a)gmail.com> wrote: > On Jul 10, 11:14 pm,dlzc<dl...(a)cox.net> wrote: > > On Jul 9, 7:51 pm, "Y.Porat" <y.y.po...(a)gmail.com> wrote: > > > On Jul 9, 7:48 pm,dlzc<dl...(a)cox.net> wrote: > > > > On Jul 9, 10:23 am, "Y.Porat" <y.y.po...(a)gmail.com> wrote: > > > > > On Jun 30, 7:52 pm,dlzc<dl...(a)cox.net> 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). > > > > > > -------------------- > > > > > see My 'Circlon'' idea !!! > > > > > Y.Porat > > > > > --------------------- > > > > > Doesn't work, even if light had mass. The mass > > > > is bound to galaxies, and there is not enough > > > > gravity to do that far from black holes. > > > > ---------------------- > > > YOU HAVE TO DECIDE ONCE AND FOR ALL > > > WHETHER TH EPHOTON HAS MASS OR NOT > > > OR ELSE YOU CANT MAKE REAL ADVANCE !!! > > > DO NOT SHOUT. > > > Your circlons still travel at c. They cannot be Dark > > Matter. That is my total concern. > >---------------------- > > did i say anything about the velocity of the Circlon ??!! > i said that its motion is a double motion You have not said how it knows to be one or the other. .... > how does your dark matter makes any attraction?? Via its mass, presumably. David A. Smith
From: dlzc on 13 Jul 2010 14:36 Dear Yousuf Khan: On Jul 12, 8:22 am, Yousuf Khan <bbb...(a)spammenot.yahoo.com> wrote: > On 7/6/2010 9:43 AM,dlzcwrote: > > On Jul 5, 2:32 am, Yousuf Khan<bbb...(a)yahoo.com> wrote: > >>> 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. > > Okay, I know you've corrected this in a later post: > > > 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. > > So does this change your opinion somewhat? My opinion that Dark Matter is an accounting mistake, no. > Does this mean there isn't enough regular invisible > matter inside galaxies to account for the Newtonian > galaxy rotation curves? Again, no I think it is all due to baryonic matter, with some contribution from neutrinos that cooled from the Big Bang (somehow), so that they could be gravitationally bound. > Also where are you getting your figures from? Which figures? So far, I've got a density for the Milky Way's galactic plane that is in a number of sources, including Wikipedia. The balance is units conversion. > >>>> 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. > > Well, I had recently posted a link about how on some > planets around red dwarfs, UV may actually be > producing more ozone, which blocks further UV > from penetrating the planet surface. > > Red Dwarfs May Be Safe Havens For Life : Discovery > News > "But there is one big catch. Young red dwarfs have > a petulant youth stretching over billions of years. > Titanic stellar flares erupt without warning and blast > out lethal doses of ultraviolet radiation. Ocean life > on a planet may be safe from the UV just a few feet > underwater and still extract enough light for > photosynthesis. But anything living on the > surface could get fried without a liberal coating of > Sunscreen 2000. Yes, the problem with an object that is "red", is that there is little to no UV-C or more energetic radiation to form ozone. So there would be no protective ozone layer until some seconds into a flare. > But we now have a glimmer of hope for red dwarf > planets. Astrobiologist Antigona Segura of the > Universidad Nacional Autónoma de México (UNAM) > in Mexico City, simulated how a 1985 flare from the > nearby red dwarf AD Leonis would have affected a > hypothetical Earth-like planet orbiting a dwarf. > Agular dwarf-large > > He found that UV radiation actually split molecules > of oxygen to create more ozone than it destroyed. Unfortunately, this takes time. > The simulation made a thicker ozone layer in the > planetary atmosphere such that the surface > experienced no more radiation than is typical on a > sunny day on Earth. <snip now broken link> Also, if there is nitrogen and significant water vapor, the atmosphere will become optically thick with "smog", as NOx forms instead. Water vapor prevents the formation of much ozone, since nitrogen (in our atmosphere anyway) serves to brake and temporarily hold the monatomic oxygen fragments. > >>> 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. > > So how does this ionized matter affect what you're > trying to prove here? Normal baryonic matter that is diffuse, Dark (to optical and longer wavelengths), and "anomalously" missing from the galaxy's center (and the M/L's method of establishing the center as somehow descriptive of the entire glowing galaxy). > >> 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... > > So you're saying that there's more ionized matter above > and below the galactic disk? We know from Andromeda that significant amounts of Dark Matter (as an effect) is required above and below the disk, to get the various "daughter bodys" of Andromeda to move as observed (with other assumptions, such as they are bound to Andromeda). Ionized matter might be a significant contributor to that effect, if not the entire player. David A. Smith
From: Steve Willner on 13 Jul 2010 18:38 > > I realise I don't understand enough about bremsstrahlung--the resulting > > energy spectrum for instance. In article <i1akt7$2em$1(a)news.eternal-september.org>, eric gisse <jowr.pi.nospam(a)gmail.com> writes: > It is proportional to the acceleration felt by the protons/electrons upon > collision, but I have no idea how to determine from my current knowledge of > particle physics. Menzel worked out the basics in the 1930's. You can consider the protons as standing still because the electrons are so much less massive. So consider one electron encountering one proton with a given speed and impact parameter. The electron's acceleration gives the radiated energy from Maxwell's equations. (I think one actually uses a different equation derived from Maxwell's equations, but I've forgotten its name.) Integrate this over all impact parameters, then put in the Maxwell distribution and integrate over velocities to get the radiation as a function of electron temperature. All that is strictly classical, and you need a quantum correction called the "Gaunt factor." I had a quick scan around for the actual numbers for X-ray wavelengths and didn't find them, but the emission at any given energy <<kT goes approximately at T^-0.1. (The classical dependence is T^-0.5, but the Gaunt factor goes roughly as T^0.4 in this regime.) The energy distribution is approximately E^-0.4 exp(-E/kT), again valid only at X-ray energies and if E is near kT. What this means is that for any gas density you choose, you can make the X-ray emission small by making the temperature high. The trouble is, high temperature means high pressure (thus effects on the observed ISM) and also the gas escapes very quickly. I haven't put in numbers, as I wrote earlier, but from comparison with typical ISM and intra- cluster values, I'd be astonished if there's any temperature regime hot enough not to be directly detectable and cold enough that the gas doesn't profoundly affect the ISM and/or blow away. > > But I just found that with the assumed plasma temperature of 25 > > megakelvin, the protons (not even the electrons) have a a thermal speed > > almost three times that of the sun's rotation about the galactic centre or > > about twice the local escape velocity... Sounds right. Essentially the hot gas expands at the sound speed unless something stops it. These energies are still far below the relativistic speeds needed for synchrotron radiation, but if one were to pursue this hypothesis, one would have to show that cyclotron radiation (radio wavelengths) isn't detectable. You could probably do that by postulating a low magnetic field strength outside the Galactic disk. As I wrote earlier, this whole idea appears to be a non-starter. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 swillner(a)cfa.harvard.edu Cambridge, MA 02138 USA
From: John Park on 14 Jul 2010 06:59
Steve Willner (willner(a)cfa.harvard.edu) writes: >> > I realise I don't understand enough about bremsstrahlung--the resulting >> > energy spectrum for instance. > > In article <i1akt7$2em$1(a)news.eternal-september.org>, > eric gisse <jowr.pi.nospam(a)gmail.com> writes: >> It is proportional to the acceleration felt by the protons/electrons upon >> collision, but I have no idea how to determine from my current knowledge of >> particle physics. > > Menzel worked out the basics in the 1930's. You can consider the > protons as standing still because the electrons are so much less > massive. So consider one electron encountering one proton with a > given speed and impact parameter. The electron's acceleration gives > the radiated energy from Maxwell's equations. (I think one actually > uses a different equation derived from Maxwell's equations, but I've > forgotten its name.) Integrate this over all impact parameters, then > put in the Maxwell distribution and integrate over velocities to get > the radiation as a function of electron temperature. All that is > strictly classical, and you need a quantum correction called the > "Gaunt factor." I had a quick scan around for the actual numbers for > X-ray wavelengths and didn't find them, but the emission at any given > energy <<kT goes approximately at T^-0.1. (The classical dependence > is T^-0.5, but the Gaunt factor goes roughly as T^0.4 in this > regime.) The energy distribution is approximately E^-0.4 exp(-E/kT), > again valid only at X-ray energies and if E is near kT. > [see below] > What this means is that for any gas density you choose, you can make > the X-ray emission small by making the temperature high. The trouble > is, high temperature means high pressure (thus effects on the > observed ISM) and also the gas escapes very quickly. I haven't put > in numbers, as I wrote earlier, but from comparison with typical ISM > and intra- cluster values, I'd be astonished if there's any > temperature regime hot enough not to be directly detectable and cold > enough that the gas doesn't profoundly affect the ISM and/or blow away. > >> > But I just found that with the assumed plasma temperature of 25 >> > megakelvin, the protons (not even the electrons) have a a thermal speed >> > almost three times that of the sun's rotation about the galactic centre or >> > about twice the local escape velocity... > > Sounds right. Essentially the hot gas expands at the sound speed > unless something stops it. If I did the arithmetic right, a realistic kinetic velocity for a stable plams would give a mean thermal energy less than 100 eV . . . so only very soft x-rays, if any? --John Park |