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#31
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Galaxies without dark matter halos?
"g" == greywolf42 writes:
g Your original argument was that EM forces could not affect neutral g hydrogen significantly -- directly or indirectly. I provided you g with two physical mechanisms that can equalize the motion of g neutral hydrogen with EM-driven motion of ionized hydrogen (which g you apparently don't have a problem with). Yes, you have "provided [...] two physical mechanisms that can equalize the motion of neutral hydrogen with EM-driven motion of ionized hydrogen." You have not shown that these physical mechanisms operate or are important in the interstellar medium. * You've asserted that there are plasma filaments with "typical widths on the order of AU to thousands of AU," but you've provided no observational evidence for them. * You continue to confuse hydrogen atoms (from which rotation curves are measured commonly) with hydrogen molecules. (See the response to John Park on 2003-08-30, as well as various postings by me.) * You continue to rely on pressure equilibrium, even though this is widely known to be true only on average (for a striking demonstration of the existence of pressure non-equilibrium in the interstellar medium, see the massive work by Jenkins & Tripp in the ApJS) and there are clear examples of shock waves in the ISM. -- Lt. Lazio, HTML police | e-mail: No means no, stop rape. | http://patriot.net/%7Ejlazio/ sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html |
#32
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Galaxies without dark matter halos?
greywolf42 ) writes:
Joseph Lazio wrote in message * You continue to confuse hydrogen atoms (from which rotation curves are measured commonly) with hydrogen molecules. (See the response to John Park on 2003-08-30, as well as various postings by me.) I'm not at all confused. The motion of ionized hydrogen (atoms) and the motion of neutral hydrogen (molecules) are both measured. Hence, the reference I gave you to Tayler. Ionised hydrogen isn't an atom; it's a proton or, at best, a molecular ion. Neutral H atoms are paramagnetic. H2 molecules are diamagnetic and don't produce the 21 cm line; so how is their motion measured? --John Park |
#33
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Galaxies without dark matter halos?
greywolf42 ) writes:
Joseph Lazio wrote in message * You continue to confuse hydrogen atoms (from which rotation curves are measured commonly) with hydrogen molecules. (See the response to John Park on 2003-08-30, as well as various postings by me.) I'm not at all confused. The motion of ionized hydrogen (atoms) and the motion of neutral hydrogen (molecules) are both measured. Hence, the reference I gave you to Tayler. Ionised hydrogen isn't an atom; it's a proton or, at best, a molecular ion. Neutral H atoms are paramagnetic. H2 molecules are diamagnetic and don't produce the 21 cm line; so how is their motion measured? --John Park |
#34
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Galaxies without dark matter halos?
"g" == greywolf42 writes:
g Joseph Lazio wrote in message g ... g Your original argument was that EM forces could not affect neutral g hydrogen significantly -- directly or indirectly. I provided you g with two physical mechanisms that can equalize the motion of g neutral hydrogen with EM-driven motion of ionized hydrogen (which g you apparently don't have a problem with). Yes, you have "provided [...] two physical mechanisms that can equalize the motion of neutral hydrogen with EM-driven motion of ionized hydrogen." You have not shown that these physical mechanisms operate or are important in the interstellar medium. g I gave you the standard text by Tayler, and excerpts from same. I finally had the chance to look at Tayler. I'll confess, I don't understand why you reference it. In Chapter 2 he discusses rotation velocities of stars and gas within the Galaxy. He cites a couple of different estimates of stellar rotational velocities, which are between 200 and 300 km/s. He also provides rotation curves derived from gas motions, which are in the range 220--240 km/s. No major discrepancy here, as Steve Willner has already pointed out. * You've asserted that there are plasma filaments with "typical widths on the order of AU to thousands of AU," but you've provided no observational evidence for them. g What type of secondary 'observational' evidence would you accept, g since we can't directly observe such without an interstellar probe? Why can't you just provide what you think to be the evidence? Moreover, Tayler describes magnetic fields in Chapter 6, citing values similar to what John Park assumed (length scales ~ 100 pc and field strengths ~ few microGauss). You've objected to both of these values, arguing for much smaller length scales and higher field strengths, but I'll have to confess I don't understand why. * You continue to confuse hydrogen atoms (from which rotation curves are measured commonly) with hydrogen molecules. (See the response to John Park on 2003-08-30, as well as various postings by me.) g I'm not at all confused. The motion of ionized hydrogen (atoms) g and the motion of neutral hydrogen (molecules) are both measured. g Hence, the reference I gave you to Tayler. This sounds like a "Yes, you do. No, I don't" argument. I can't do any more than say that, after re-reading your posts on Google, I continue to think you do not make this distinction. Perhaps if you were to supply a succinct summary of your idea it would clear up some confusion. * You continue to rely on pressure equilibrium, even though this is widely known to be true only on average (...) and there are clear examples of shock waves in the ISM. g You asked for evidence that pressure could equalize the rotation g rates of ionized and non-ionized gas. If -- as discussed in Tayler g -- "ionized gas clouds and non-ionized gas clouds roughly maintain g equal pressures between region boundaries," then the time scale for g maintaining these equal pressures must be far less than the time to g orbit the center of the galaxy. Otherwise, there wouldn't *be* g different regions. g Yes, it is the 'average' situation. And the average situation is g what we look at when we measure overall galactic rotation curves. The "average" that Tayler forms is over kiloparsec scales. You seem to assert that pressure equilibrium continues to hold even on sub-parsec scales. That's a huge extrapolation, and one for which we have some evidence to the contrary. Admittedly, I was browsing through Tayler's text after midnight last night. I could have missed something. Perhaps you might provide a succinct summary of your idea (and the evidence supporting it?) to clear up the confusion? -- Lt. Lazio, HTML police | e-mail: No means no, stop rape. | http://patriot.net/%7Ejlazio/ sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html |
#35
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Galaxies without dark matter halos?
"g" == greywolf42 writes:
g Joseph Lazio wrote in message g ... g Your original argument was that EM forces could not affect neutral g hydrogen significantly -- directly or indirectly. I provided you g with two physical mechanisms that can equalize the motion of g neutral hydrogen with EM-driven motion of ionized hydrogen (which g you apparently don't have a problem with). Yes, you have "provided [...] two physical mechanisms that can equalize the motion of neutral hydrogen with EM-driven motion of ionized hydrogen." You have not shown that these physical mechanisms operate or are important in the interstellar medium. g I gave you the standard text by Tayler, and excerpts from same. I finally had the chance to look at Tayler. I'll confess, I don't understand why you reference it. In Chapter 2 he discusses rotation velocities of stars and gas within the Galaxy. He cites a couple of different estimates of stellar rotational velocities, which are between 200 and 300 km/s. He also provides rotation curves derived from gas motions, which are in the range 220--240 km/s. No major discrepancy here, as Steve Willner has already pointed out. * You've asserted that there are plasma filaments with "typical widths on the order of AU to thousands of AU," but you've provided no observational evidence for them. g What type of secondary 'observational' evidence would you accept, g since we can't directly observe such without an interstellar probe? Why can't you just provide what you think to be the evidence? Moreover, Tayler describes magnetic fields in Chapter 6, citing values similar to what John Park assumed (length scales ~ 100 pc and field strengths ~ few microGauss). You've objected to both of these values, arguing for much smaller length scales and higher field strengths, but I'll have to confess I don't understand why. * You continue to confuse hydrogen atoms (from which rotation curves are measured commonly) with hydrogen molecules. (See the response to John Park on 2003-08-30, as well as various postings by me.) g I'm not at all confused. The motion of ionized hydrogen (atoms) g and the motion of neutral hydrogen (molecules) are both measured. g Hence, the reference I gave you to Tayler. This sounds like a "Yes, you do. No, I don't" argument. I can't do any more than say that, after re-reading your posts on Google, I continue to think you do not make this distinction. Perhaps if you were to supply a succinct summary of your idea it would clear up some confusion. * You continue to rely on pressure equilibrium, even though this is widely known to be true only on average (...) and there are clear examples of shock waves in the ISM. g You asked for evidence that pressure could equalize the rotation g rates of ionized and non-ionized gas. If -- as discussed in Tayler g -- "ionized gas clouds and non-ionized gas clouds roughly maintain g equal pressures between region boundaries," then the time scale for g maintaining these equal pressures must be far less than the time to g orbit the center of the galaxy. Otherwise, there wouldn't *be* g different regions. g Yes, it is the 'average' situation. And the average situation is g what we look at when we measure overall galactic rotation curves. The "average" that Tayler forms is over kiloparsec scales. You seem to assert that pressure equilibrium continues to hold even on sub-parsec scales. That's a huge extrapolation, and one for which we have some evidence to the contrary. Admittedly, I was browsing through Tayler's text after midnight last night. I could have missed something. Perhaps you might provide a succinct summary of your idea (and the evidence supporting it?) to clear up the confusion? -- Lt. Lazio, HTML police | e-mail: No means no, stop rape. | http://patriot.net/%7Ejlazio/ sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html |
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