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Re: Elements

Dave,
Just being anal, but the orignal bounce from the core collapse
stalls out. The process of the rejuevenation is not completely
understood but it's mostly believed that neutrinos play a role. I will
try to find out more if anyone wants. Also, the core-collapse supernova
is a very fast process, less than a second (that has always impressed
me).


Sam Held


-----Original Message-----
From: David Bowman [mailto:dbowman@TIGER.GEORGETOWNCOLLEGE.EDU]
Sent: Saturday, February 27, 1999 12:44 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Elements


Where/when were the elements produced?

Hydrogen, helium, and a small smattering of lithium were produced in the
big bang. More helium, is made in the cores of main sequence stars where
hydrogen is consumed. Carbon and oxygen are made in the cores of red
giant stars where helium is consumed. Surrounding such a core is a
layer
that fuses hydrogen into helium. In very high mass stars that are
almost
about to go supernova is an onioneque layered structure that has
different
elements formed in each layer with the with the higher mass elements
formed in the inner layers and the lighter mass elements formed in the
outer layers. The highest mass element made in the highest mass stars
is
56Fe. When the core of such a star collapses (due to a shortage of the
"fuel" to make more Fe, then the iron core of the star implodes into a
core of neutrons followed by a bounce that blasts the star apart into a
type II supernova. The energy released in the supernova explosion shock
wave funds the endothermic reactions which fuses all the rest of the
heavier elements (as well as making significant quantities of highly
radioactive isotopes of all masses and kinds).

Why were not they all produced in the so called "big bang"?

Because the universe expanded too fast. The temperature and density of
matter fell below the threshold necessary for further fusion reactions
to take place quite early on before the higher mass elements had a
chance
to build up.

David Bowman
dbowman@georgetowncollege.edu