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From: pfennige@uni2a.unige.ch
Newsgroups: sci.space,sci.astro
Subject: Re: Dark matter
Message-ID: <1991Jun17.093521.991@uni2a.unige.ch>
Date: 17 Jun 91 07:35:21 GMT
References: <1991Jun11.165204.6159@isc.rit.edu> <10705@suned1.Nswses.Navy.MIL>
Organization: University of Geneva, Switzerland
Lines: 16

In article <10705@suned1.Nswses.Navy.MIL>, lev@slced1.nswses.navy.mil (Lloyd E Vancil) writes:
...
> And I was wondering, why cant "dark matter" be planets, rocks, comets, etc etc?

Heavy atomic elements heavier than He are thought to have been synthesized
mainly by massive stars, because first these stars evolve in a short time
(~10^7 y), and second they eject most of their processed mass back into the
interstellar medium (such as supernovae).  So the possibility of rocky planets
such as the earth depends on the previous evolution of massive stars.  Now,
when stars form from a gas cloud, most of the mass is going into low mass
stars, which evolve very slowly (>10^9 y).  In conclusion it seems very
difficult to make dark matter by mainly heavy elements, because their
processing needs to lock even more mass in low mass stars, for a time as long
or longer than the age of the Galaxy.  

	Daniel Pfenniger