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Topic: This Week's Finds in Mathematical Physics (Week 238)
Replies: 7   Last Post: Aug 30, 2006 7:43 AM

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Phillip Helbig---remove CLOTHES to reply

Posts: 33
Registered: 12/13/04
Re: Dark Matter, QSOs and Microlensing
Posted: Aug 29, 2006 6:00 AM
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In article <1156736105.638769.183650@74g2000cwt.googlegroups.com>,
"rloldershaw@amherst.edu" <rloldershaw@amherst.edu> writes:

> For a while I had hoped that QSO variability might be a good route to
> elucidating the nature of the dark matter, based upon the work of
> Hawkins, Schild, Burud and many others who monitored QSOs, blazars,
> radio galaxies, etc. This observational strategy may yet yield crucial
> evidence on the dark matter issue, but I now think microlensing
> observations within the Local Group are a more dependable route to the
> desired goal.


I think it is fair to point out that while Hawkins's first papers on
this, in Nature and MNRAS, were interesting, well written and put
forward a good, falsifiable hypothesis (and also that many of the early
rebuttals attacked a straw-man caricature of his ideas, perhaps
disproving a specific scenario but not the idea in general), the idea
really doesn't stand up to a quantitative statistical analysis. I don't
think Hawkins has accepted this and sees himself as somewhat of a
misunderstood genius (see his popular book HUNTING DOWN THE UNIVERSE
(which I purchased by chance at a music festival in Oxfordshire some
years ago!)). Also, Rudy Schild's ideas on QSO variability are, to put
it nicely, not accepted in general by the astronomical community. I
don't think they stand up too well myself, either. His observations,
though, are fine.

The problem with the Local Group in this context is that it is small
relative to the universe, so it is difficult to extrapolate any density
of compact objects to get a fraction of dark matter on the cosmological
scale.

> We are making progress. Experiments have shown that dark matter
> unambigously exists. Experiments have also shown that a significant
> portion of the dark matter is composed of stellar-mass objects, and
> that the dark matter mass function parallels the SMF in a most
> provocative way.


Dark matter on a galactic scale, i.e. that necessary to explain rotation
curves, or dark matter in the sense of the difference between the
cosmological Omega value (0.3 or so) and the small fraction accounted
for by luminous matter (or, in a slightly different definition, the
fraction in baryonic matter)?




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