eklhad@ihnet.UUCP (K. A. Dahlke) (06/27/85)
< H He C N O Si Fe > A recent scientific American article (May i believe) described the explosion of a super nova. This fascinating article gave a simplified scenario of stellar evolution, burning hydrogen, helium, carbon, nitrogen, oxygen, silicon, and 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? Are intermediate elements produced by radioactive decay of iron, silicon, etc? Are higher elements produced in very small quantity, due to equilibrium reactions in the stellar core, similar to N2+3h2 <> 2NH3? Gold atoms must have come from somewhere, and I don't believe in a creator. Any help appreciated. -- Is it time to go home yet? Karl Dahlke ihnp4!ihnet!eklhad
rcf@inuxd.UUCP (R Fitch) (06/27/85)
*** REPLACE THIS LINE WITH YOUR MESSAGE *** <A recent scientific American article (May i believe) <described the explosion of a super nova. <This fascinating article gave a simplified scenario of stellar evolution, <burning hydrogen, helium, carbon, nitrogen, oxygen, silicon, <and 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? <Are intermediate elements produced by radioactive decay of iron, silicon, etc? <Are higher elements produced in very small quantity, due to equilibrium <reactions in the stellar core, similar to N2+3h2 <> 2NH3? <Gold atoms must have come from somewhere, and I don't believe in a creator. <Any help appreciated. I HAVE A FURTHER QUESTION!!WHERE DID THE; HELIUM,CARBON,NITROGEN, OXYGEN AND SILICON COME FROM LET ALONE THE GOLD????????? --
andrew@alberta.UUCP (Andrew Folkins) (06/28/85)
In article <243@ihnet.UUCP> eklhad@ihnet.UUCP (K. A. Dahlke) writes: >< H He C N O Si Fe > > A recent scientific American article (May i believe) >described the explosion of a super nova. >My question is, how did the other elements form; >especially those above iron? The elements up to iron are created by a process called nucleosynthesis, in which smaller atoms fuse together to produce larger ones. The fusion of elements up to iron produces energy, while the fusion of atoms heavier than iron absorbs energy. Thus, silicon fusion will produce enough energy to keep the star going (for a day or two, I think the figure was), while iridium fusion would suck up energy and cause the star to collapse under it's own weight (it's normally supported by radiation pressure from the fusion processes in the core). Elements heavier than iron require extra energy to produce, energy not normally present in the core of a star. The energy is found, however, in supernova explosions, where the temperatures and pressures of the collapsing core are sufficient to produce the remaining natural elements. When the core rebounds, producing the actual explosion, some of these 'impurities' are blasted out into space, where, after billions and billions of years, they condense to form ingots in bank vaults :-). I think I'll go re-read that article, it _was_ quite interesting. -- Andrew Folkins ihnp4!alberta!andrew Underlying Principle of Socio-Genetics : Superiority is recessive.
rh@mit-eddie.UUCP (Randy Haskins) (06/29/85)
About forming the elements heavier than Fe: It turns out that in its dying days (years, whatever), a star will actually form the heavier elements by fusion. The problem is, this is an endothermic sort of thing; it requires more energy than it produces. As time goes on, the situation in the star is going to head for its lowest energy state. A supernova, on the other hand, is a situation where a large amount of energy is liberated in a short time, and the heavier elements will be formed more than they would be inside the star. Also, when the supernova does its thing, it blows a lot of the material (including the heavier elements it has formed) out into space, so they won't be around it the star any more to be decayed by fission. A real astronomer could probably explain this better than I did, but this is the gist of the situation as I understand it. Hope it helps. -- Randwulf (Randy Haskins); Path= genrad!mit-eddie!rh
john@frog.UUCP (John Woods) (06/29/85)
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.
jeff@utastro.UUCP (Jeff Brown the Scumbag) (06/30/85)
> >My question is, how did > >the other elements form, especially those above iron? > > > 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. Pretty much right. To be monotonously complete about it, here's more. Hydrogen, helium, and some lithium were produced in the Big Bang. (Helium is also made in the "common" hydrogen fusion reactions that power the stars most of their lives, but there's a neat calculation first done by Hoyle which shows that most helium atoms are primordial -- i.e., from the Big Bang.) Li, Be, and B are thought to arise principally in the interstellar medium by spallation processes with cosmic rays; that is, cosmic ray particles smack into other nuclei, shattering them and producing small amounts of these light-element nuclei (the whole process is very much like a collision in a terrestrial particle accelerator). Things from carbon to nickel are made principally by fusion of helium, and things produced by fusing helium. The first step is the "famous" triple- alpha process: three He's -> one C. Another He nucleus onto this gives one oxygen nucleus. Fuse two oxygen nuclei and you can get lots of things (the reaction chains get messy at this kind of energy), but often it's one silicon or a magnesium plus other a helium, etc. This works up to about iron and nickel. > 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. > Sort of. Heavy element synthesis is a fascinating web of sites and processes, but not all of it can be blamed on supernovae. Even there, though, you don't continue to make things by standard fusion of regular nuclei (a side note is that "regular nuclei" get scarce in a pre-supernova core -- it's a pretty messed-up little volume). Past the "iron peak" (Fe, Co, Ni) things are produced by neutron capture, for the most part. There are a couple of reactions in the chain which produce lots of neutrons. Neutron capture can go on at lower temperatures than other things (neutrons, being neutral, don't have to overcome the charge barrier that works against regular fusion reactions), and many heavy nuclei are made by feeding iron nuclei one neutron at a time for a few million years. (This is the slow neutron capture process, or "s-process" in the business.) If you generate huge numbers of neutrons in one shot -- and this is where supernovae enter the picture, since doing this is very tough on the local architecture -- you can dump scads of neutrons on one nucleus in one shot (the rapid or "r-process") and make nuclei that way. This is where the actinides (uranium and its daughters) come from. Details of nuclear physics determine whether a nucleus (I don't say "element" here because different isotopes of the same element can have different origin!) is of s- or r- (or other! there's a lot more to it) process origin. To get specific, gold has one stable isotope which is generally considered to be an r-product, so the gold in your teeth (or mine, if you've taken better care of yours than I have) did come from some obliging supernova.
paul@uiucuxc.Uiuc.ARPA (07/02/85)
The energy released in a supernovae explosion provides the energy
necessary to drive the endothermic (energy absorbing) fusion reactions
that produce elements heavier than iron. These elements are formed
and then thrown out into interstellar space. Later stellar evolution
incorporates these elements into new stars and planets.
Paul Pomes
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ARPANET: paul%uiucuxc@uiuc.arpa
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