Question about origins of elements

[sathearn]

I just joined the forum, so excuse me if I'm late to the discussion. But thanks to dangerbird for posing the question about how we know that the heaviest elements are produced in supernovae. Malawi_glenn provided an obvious answer regarding how we might now this, without referring to actual results of observations of supernovae:

one can measure spectrum of stars and supernovae and find out which and how much elements there are.. how do we know that the sun is made up of mainly hydrogen? Well we look at and analyse the solar spectra...

Now consider the following statement:

"The relative abundance of these [heavy] elements in the supernova is not very different from their abundance in the sun. If the supernovae sythesize heavy elements out of lighter ones in the course of their explosion, none of that material is initially seen in the rapidly expanding debris."
(Robert P. Kirschner, Scientific American, Dec., 1976, as quoted in Dewey B. Larson, Universe of Motion, Portland: North Pacific, 1984, p. 34; see also web version at http://library.rstheory.org/books/uom/03.html )

So my question is, what is the actual evidence from supernovae spectra telling us? Has the observational situation changed materially since Kirschner and Larson wrote?

 

[Scientus]

As long as we are on the subject, how do we know that heavy elements weren't created in the early universe ? Weren't temperatures and pressures as high as in a supernova?

 

[Chronos]

Extreme temperatures are necessary to fuse heavy elements. It is essentially a matter of forcing enough protons together long enough to acquire the electons necessary to form a stable nucleus. The temperatures necessary to fuse elements heavier than iron/nickel can only be achieved in supernova. While the very early universe was indeed very hot, it lacked one essential ingredient - protons. This is why hydrogen was not formed until the latter stages of the big bang,

 

[Nabeshin]

Extreme temperatures are necessary to fuse heavy elements. It is essentially a matter of forcing enough protons together long enough to acquire the electons necessary to form a stable nucleus. The temperatures necessary to fuse elements heavier than iron/nickel can only be achieved in supernova. While the very early universe was indeed very hot, it lacked one essential ingredient - protons. This is why hydrogen was not formed until the latter stages of the big bang,

From what I understand, it is not so much a lack of protons that caused the lack of synthesis of heavier elements but more the lack of time. Namely, since heavier elements are built, essentially, out of multiples of helium nuclei, you need to fuse helium first to get anything heavier. There simply wasn't enough time to fuse a substantial quantity of helium in order to build up the chain to heavier elements (and, quite possibly, a lack of helium during the early phase of nucleosynthesis where temperatures were still very hot).

 

[sathearn]

Thanks for these elaborations of the theory. To restate my question, does the theory not lead to predictions about supernovae spectra (as the quote from malawi_glenn implied)? And what is the current state of the observational evidence on supernovae spectra, given Kirschner's statement that heavier elements are not seen?

 

[Chronos]

Doppler broadening and line blending in supernova spectra makes identification of heavy elements observationally challenging. Isolating their spectral lines from the bright glow of more abundant lighter elements is an issue.

 

[Chronos]

Good clarification, Nabeshin. By the time protons froze out of the chaotic mess left over from the big bang, there was only enough time left to fuse elements up to around the atomic weight of lithium.

 

[sathearn]

Thanks for the clarification, Chronos.