Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 beta 3/9/83; site frog.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!mtuxo!mtunh!mtung!mtunf!ariel!vax135!timeinc!phri!pesnta!amd!amdcad!decwrl!decvax!genrad!mit-eddie!cybvax0!frog!john From: john@frog.UUCP (John Woods) Newsgroups: net.astro.expert Subject: RE:Forming The Elements Message-ID: <213@frog.UUCP> Date: Sat, 29-Jun-85 16:41:38 EDT Article-I.D.: frog.213 Posted: Sat Jun 29 16:41:38 1985 Date-Received: Wed, 3-Jul-85 08:01:56 EDT References: <243@ihnet.UUCP> <776@inuxd.UUCP> Distribution: net Organization: Charles River Data Systems, Framingham MA Lines: 36 Someone: >A recent scientific American article described the explosion of a supernova. >This fascinating article gave a simplified scenario of stellar evolution, >burning hydrogen, helium, carbon, nitrogen, oxygen, silicon, finally >producing iron. Paraphrasing: "Once a central core of iron is produced, >reactions cannot continue. Larger nuclei exist, but their formation >is not favored. Iron is the lowest energy nucleus." My question is, how did >the other elements form, especially those above iron? SOMEONE ELSE: > I HAVE A FURTHER QUESTION!!WHERE DID THE; HELIUM,CARBON,NITROGEN, > OXYGEN AND SILICON COME FROM LET ALONE THE GOLD????????? > -- > First, He, C, N, O, and Si are formed "recursively" (:-) by fusing lighter nuclei (starting with hydrogen) to yield heavier nuclei and free energy. The problem with creating anything heavier than iron is that you don't get energy out of it, it costs energy (as a chemist would say, the reaction is endothermic, not exothermic). Thus, it doesn't happen spontaneously (at least, not frequently). However, in a supernova (surprise!) there is scads of energy floating around, which is more than sufficient to overcome the energy hump of slamming even heavy nuclei together to fuse them; so much energy, in fact, that the heavy fusion reactions do not noticably cool things down. It is exactly analogous to standard chemistry, where if you want to drive a reaction in reverse (from the low energy state to the high energy state), all you need do is provide lots of reactants and some energy (plus a way to extract the results before it breaks up). -- John Woods, Charles River Data Systems, Framingham MA, (617) 626-1101 ...!decvax!frog!john, ...!mit-eddie!jfw, jfw%mit-ccc@MIT-XX.ARPA This has been a public disservice announcement.