🚀 go-pugleaf

bweiner@ruhets.rutgers.edu (Benjamin Weiner) writes:
|> joe@astro.as.utexas.edu (Joe Wang) writes:
|> >Now, current estimates of the primordial helium abundance give about
|> >25%+/-10%.  It's the plus or minus 10% which is interesting.  If
|> >better measurements indicate that the early helium abundance is less
|> >than 20%, the Big Bang has big, big problems.
|> 
|> True.  On the other hand I don't think anyone has actually claimed
|> to have found an object with less than 20-some percent helium.
|> (Asteroids excluded :-)  But also, nobody has found any stars or
|> other objects with absolutely zero metallicity.  This is annoying,
|> because it means that metals have to be synthesized before globular
|> cluster stars form, which probably means during galaxy formation,
|> and I'm not sure there are any real good ideas for doing that.
|> Supercolossal stars, etc., seem somewhat contrived.  Maybe giant
|> amounts of shock heating would do it.  (The problem is that you
|> have to get some kind of hot thing to make the metals - e.g. so-
|> called Population III stars; but then you have to make it go away,
|> because we don't see it now.  If Pop III included small, slightly 
|> under solar mass stars, they would still be around.)
|> 

Just another comment on this.  Pop III or primeval galaxies usually
get invoked to ionize the intergalactic medium at high redshift and
explain the missing Gunn-Peterson trough in QSO spectra.  There really
is no question that there is an IGM; to satisfy the Gunn-Peterson
constraint, it must be hot (T > 10^5 K).  If the mechanism involved in
heating it up is stellar in origin (early galaxies, Pop III, etc.), then
you're going to get metals mixed in.