Quote:
Originally Posted by Peter Wilson
[snip]
And Yes, Nereid, dust is transparent to gamma and radio waves. Every substance has its “absorption spectrum.” Dust just happens to be particularly absorbent near the peak emission range of most stars, and hydrogen particularly transparent.
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As good an example of the pitfalls of 'word salad' physics if ever there was one.
First, H is most certainly NOT transparent, blue-ward of the Lyman limit.
Second, 'most stars' is irrelevant (or, if you prefer, marginally relevant); what counts is the integrated SED of a galaxy ... to which 'most stars' contribute little (they're too dim), and where they do contribute (in the infrared), 'most dust' is transparent.
Third, at least in rich clusters, stars (and dust, and all the mass in galaxies) is pretty much irrelevant ... the known mass of inter-galactic gas (actually plasma) far exceeds that of the mass in galaxies.
Fourth, in terms of numbers of photons, the CMB outnumbers all the emissions from all the stars, dust, galaxies, hot plasma, cold gas, ... combined (and dust is essentially transparent to the CMB .... except, of course, that it radiates in this waveband!)
Fifth, outside of spiral and (some) irregular galaxies, there is (essentially) no dust.
(and so on).
So if dust is so important, then why doesn't DEILE work ONLY on spiral (and some irregular) galaxies? And why isn't hydrogen gas far more important in star-burst galaxies (where the SED is dominated by UV, from the massive stars in the star-bursts)?
Quote:
But all-and-everything makes some contribution, at some wavelength, at some distance. It is said that it would take 10 light-years of lead to stop neutrinos. Well, between here and infinity lies 10 lys of lead. The neutrinos the sun spews forth make an impact…though it be far, far away. Space is nearly transparent to many types of radiation, but it is not perfectly so to any. Every part of the 70 trillion pounds of force the sun puts out makes an impact somewhere, sometime.
For DEILE model, the effect of this outward-directed radiation pressure is crucial.
[snip]
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IIRC, we had a look at this, earlier in this thread, and concluded that it holds no water ... "
this outward-directed radiation pressure" can be relevant only where it is absorbed ... which is by dust, which occurs only in spiral (and some irregular) galaxies ....
