NetNews Usenet Archive 1992 #18/NN_1992_18.iso/spool/sci/physics/13019

Internet Message Format | 1992-08-18 | 3.3 KB

Path: sparky!uunet!cis.ohio-state.edu!rutgers!dziuxsolim.rutgers.edu!ruhets.rutgers.edu!bweiner
From: [e-mail] (Benjamin Weiner)
Newsgroups: sci.physics
Subject: Re: Hubble constant?
Message-ID: <[e-mail]>
Date: 19 Aug 92 01:15:05 GMT
References: <[e-mail]> <[e-mail] <[e-mail]> <[e-mail]>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 53

John Baez writes:
>Okay, my curiosity is piqued: what's a Pop III star remnant?  After a
>star pops 3 times all that's left is remnants?  :-)

Hope no one minds a little astro-essay.  This post comes with no
implied warranty of reliability or fitness for advertised use.

As Ted Bunn said, population III stars are (hypothetically) formed
early and would now all be essentially invisible collapse remnants.
In defense of the tortured notation, pop I and pop II stars were named
that a long time ago before the relation was known.  It's not quite
true that pop II are just predecessors of pop I though.  Pop II stars
are old, hence the big short-lived ones have all died, sending
enriched gas out into the galaxy, out of which condense new stars;
our sun is considerably younger than the galaxy.  However there are
plenty of old stars still around, especially in the globular clusters;
these are the smaller, redder Pop II stars which are much longer lived
(and give us problems by seemingly being older than the universe :-)

Clearly there is a whole continuum of star ages, beginning at the
formation of the galaxy, so why the division into only two categories?
Well, although there are stars of all ages around, the most light
comes from essentially two classes of stars: bright old red giant stars
(which despite the name are only about one solar mass), and bright
young blue stars.  Hence, Pop II, and Pop I.  Globular clusters and
elliptical galaxies are red, almost all Pop II stars; the light from
spiral arms is mostly from Pop I bluish stars even though there are
plenty other stars in the arms.  In fact the beautiful photos of
spiral galaxies exaggerate the density of the arms relative to the
rest of the disk, because 1) there are more young bright stars in the
arms and 2) the photographic plates are usually more sensitive to blue
than red.  As usual in astronomy, appearances are deceiving.

>Photinos don't sound dull to me, unless like all superpartners they are
>designed to be utterly indetectible.

They'd be great for physics, but they wouldn't do anything interesting
other than gravitate for astronomy.  For example there's a certain lowest
metallicity (= % of elements above H and He) for all measured galactic
stars.  There are no stars known to have zero metallicity.  One way to
explain this is to invoke a now-invisible generation of Pop III stars
which pre-enriches the protogalactic gas to some nonzero metallicity.
Photinos can't do that (especially if they don't exist heh heh).

>I have a theory that everyone here on usenet has a superpartner: an evil
>twin that looks just like them but is 1000 times heavier.  The reason
>why nobody has ever seen one of these superpartners is that they never
>make their appointments.  :-)

I'm Dale Bass's evil twin.  Or maybe I'm Dale Bass.  Have you ever
seen me and Dale in the same room at the same time?

Ben Weiner