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From: Phillip Helbig---undress to reply <hel...@astro.multiCLOTHESvax.de>
Newsgroups: sci.astro.research
Subject: Re: Cooray et al - A Possible Solution to IR/X-ray Correlation?
Date: Thu, 25 Oct 12 17:16:47 GMT
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[Note to moderator: I don't like the long lines.  I have rewrapped them 
for clarity.]

In article <mt2.0-26204-1351179...@hydra.herts.ac.uk>, "Robert L. 
Oldershaw" wrote:

> If the DM halos are mainly composed of stellar-mass and planetary-mass
> ultrcompacts, i.e., black holes, then this model might also explain the
> ARCADE-2 radio excess.

Question: Did your model PREDICT this excess?  If not, why not, since 
the identity of the DM is clear in your model?

> In the early universe galaxies were far more crowded and interactions
> were the norm.  One would expect that much more accretion was occurring
> in the DM halo and consequently the X-ray luminosity of the DM objects
> would be much higher than in the late universe. The radio excess could
> be explained as the redshifted X-ray radiation. 

> [Mod. note: !!! -- mjh]

Indeed!  X-rays have a wavelength of about 10^{-10} metres while radio
waves have a wavelength of about 10^{-1} metres.  (Definitions vary, and
both cover a few orders of magnitudes, but we don't need that precision
here.)  This corresponds to a redshift of 10^9.  Roughly speaking, the
present density of the universe is about that of a hydrogen atom per
cubic metre, so this would mean a 10^27 increase in density, or about
that of a kg per cubic metre.  The Sun has about the same density as
water, i.e. a tonne per cubic metre, i.e. 1000 times more. Thus, at this
redsfhift the density would correspond to a solar mass per 1000 solar
volumes, or per cube with sides of about 8 million km.  The radius of
the orbit of Mercury is about 60 million km.  So, yes, it would be 
crowded and there would be much more interaction.  But the redshift of 
the CMB is only 1000, or a million times less.  Since the CMB 
corresponds to the time when the universe became optically thin, 
whatever radiation, from whatever source, which existed before then 
would be part of the thermal CMB.

In other words, X-rays which are redshifted into the radio range would 
be at a redshift a million times that of the CMB and hence would not be 
visible as radio excess.  They would, essentially, be part of the CMB, 
but the CMB is not the radio excess here.  (Note, by the way, that by 
far the majority of photons in the universe are in the CMB.)