From: Spike Jones (spike66@attglobal.net)
Date: Sun Dec 10 2000 - 22:16:35 MST
Spike Jones wrote:
> Is there a way to calculate an upper bound on the density
> of dust between stars? Does the degree of polarization of the
> spectrum from a distant star allow some upper bound? Is
> there a way to lower bound the problem? spike
Wait, I think I can upper bound the density knowing that
there is no more than 10 times the amount of matter in the
universe than is visible in the stars. Otherwise the universe
would be obviously closed. Right?
So if the sun is about 2E30 kg and there are 1E11 solar
masses of stars in the galaxy and all the dark matter is
in the form of interstellarlopers, then that is 2E41 kg
stars and so 2E42 kg dust. If the galaxy is approximately an
oblate spheroid with an effective maximum radius of 50
thousand light years, then its volume is about 1E53 cubic
kilometers, and that gives us an upper bound density of
2E-8 kg per cubic kilometer or 20,000 nanograms per
cubic kilometer. Please someone check my reckons.
Nowthen, I think we can lower bound the problem
by estimating the probability of a hit on a detector.
If the density is way less than a nanogram per
cubic kilometer, it is unlikely we would have ever
detected any of the stuff. Looks like we are within
5 orders of magnitude of the answer, unless I goofed
the lower bound, which is entirely possible since I did
not account for the concentrating effect of the sun's
gravity well. spike
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