From: schinder@leprss.gsfc.nasa.gov (Paul J. Schinder)
Newsgroups: talk.origins,sci.astro
Subject: Re: stars & carbon
Date: 21 Jul 92 18:41:43 GMT
Reply-To: schinder@leprss.gsfc.nasa.gov
Organization: Goddard Space Flight Center

In <btd.711738938@pv7413.vincent.iastate.edu> btd@iastate.edu (Benjamin T Dehner) writes:

>In <1992Jul21.152437.3950@linus.mitre.org> m23364@mwunix (James Meritt) writes:

>>Given a preference for carbon-based life, I started wondering...

>>carbon is a product of a massive stellar event (boom!), right?  If so,

>Not quite.  Any moderately heavy star is capable of forming carbon without
>going supernova.  It is part of a natural fusion sequence which can go clear

True, but getting it into the interstellar medium so it can form new
stars isn't so easy.  I believe (I could be wrong, I'm not up to date
on stellar nucleosynthesis) that supernovae are the major contributors
to the heavy element abundance (stuff formed in stars that don't SN
mostly just stays there).

>up to iron.  Above iron is where you need a supernova to form things, since
>these elements require more energy to form than can be given off in a fusion
>process -- energy available in supernova.

>>is the locale from which OUR heavy elements were fused known?  Where?

>Yeah -- right here.  (Sorry :).  No.  The original source is not known, at
>least to my knowledge.  It is believed the solar system was formed from an
>interstellar gas cloud coalesced by a combination of self-gravity and pertur-
>bations from nearby stars.  The gas cloud is assumed to have come from the
>remnants of old stars/nova/supernova, but the actual location of these objects
>is unknown.  

Right.  There's considerable mixing and diffusion going on in the ISM,
as I recall, so the answer is probably "lots of places".

>>And given that some such event has too occur first, how old would the
>>universe (heavy in H, HE & a touuch of Li) have to be for a star to
>>form, age, zap, then a new reform from the waste (i.e. how long ago COULD
>>life-as-we-know-it form someplace?)

>A supermassive star can form and go boom in about 10-20 million years.  This
>number is stronly dependant on the metalicity (percent of stuff heavier than
>helium) present.  I would hazard a guess that a couple of billion years may
>suffice to form a region of heavy elements that may work for forming life.
>As an oblique answer to your question, "long, long ago, in a galaxy ..".
>In this neck of the woods, life forming somewhere else a few million years ago
>would not be unreasonable, I think.

I think you mean "a few billion years after the galaxy formed", which
sounds about right.  In this neck of the woods we know at least one
place where life formed 4 billion or so years ago :-)

>>--
>>James W. Meritt:  m23364@mwunix.mitre.org - or - jmeritt@rod.mitre.org
>>The opinions above are mine.  If anyone else wants to share them, fine.
>>They may say so if they wish. The facts "belong" to noone and simply are.

>-----------------------------------------------------------------------------
>Benjamin T. Dehner          Department of Physics and Astronomy 
>btd@iastate.edu             Iowa State University 
>                            Ames, IA 50011

>Campus Crusade for Cthulhu  -- Smile, Cthulhu loathes you.
--
--------
Paul J. Schinder
NASA Goddard Space Flight Center
schinder@leprss.gsfc.nasa.gov
Newsgroups: talk.origins