Question about origins of elements

[dangerbird]

how is it known that iron is formed in stars and not anything heavier? And how is it known that elements like uranium arent in fact formed in the cores of stars prior to supernova? answers much appreciated

 

[Vanadium 50]

Neither of those statements are true. (Hence the "how is it known" part is superfluous)

 

[leroyjenkens]

Neither of those statements are true. (Hence the "how is it known" part is superfluous)

Uranium is formed in the cores of stars prior to a supernova?

 

[Vanadium 50]

Maybe I am having trouble parsing all those negatives.

 

[dangerbird]

Neither of those statements are true. (Hence the "how is it known" part is superfluous)

so what's the evidence for the idea that elements heavier than iron don't form in the core of a star like al lthe others do? is it an assumption based on the fact that the binding energy of iron is higher than the released energy? is that all the evidence? i can't really think of how to search this through google

 

[malawi_glenn]

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...

 

[dangerbird]

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...

can solar spectra be used to determine that stars don't form heavier than iron like the rest of the elements? say if someone were to say that in fact elements heavier than iron DO form just like all the others, would there be much evidence or any to prove them wrong?

 

[malawi_glenn]

can solar spectra be used to determine that stars don't form heavier than iron like the rest of the elements? say if someone were to say that in fact elements heavier than iron DO form just like all the others, would there be much evidence or any to prove them wrong?

OMG didn't you understand that it was just an example? It was clearly linked to "how do we know that the sun is made up of mainly hydrogen?"

Clearly, one should analyse other stellar spectra as well... DUH!

 

[DecayProduct]

Elements heavier than iron do form in the cores of stars, otherwise where would they come from? I think the idea is that no self-sustaining endothermic fusion reaction will create elements heavier than iron. So, we have to wait until the core collapses and dumps copious quantities of external energy into the existing iron and other heavy elements there, before exploding.

We do the same thing in the laboratory by slamming say gold nuclei into tungsten targets. But exploding stars do it on a much grander scale.

 

[malawi_glenn]

Elements heavier than iron do form in the cores of stars, otherwise where would they come from?

Supernovae ... r-process

 

[DecayProduct]

Supernovae ... r-process

Haha! I'm not sure how to read this! I mean, that's what I said further down my post, so I'm not sure if you are correcting me, or confirming me! Haha!

 

[malawi_glenn]

Haha! I'm not sure how to read this! I mean, that's what I said further down my post, so I'm not sure if you are correcting me, or confirming me! Haha!

I could not understand the rest of that post, so I thought I just answer that question you posed ;-)

 

[DecayProduct]

I could not understand the rest of that post, so I thought I just answer that question you posed ;-)

Why? Was I that wrong? Or did I just not word it right?

What I was saying is that nuclear fusion reactions can be self-sustaining using any fuel with nuclei less than the mass of iron. Nuclear fusion using elements heavier than iron can take place, but will not be self-sustaining because they actually require that energy be input. I think the terminology is that stars fuse elements exothermically (I said endo- in the other post incorrectly), and releasing energy. So stars with iron fuel cannot keep generating energy by creating elements heavier than iron.

When a star goes supernova, some of the material is slammed into other material at energies great enough to cause elements heavier than iron to form. A sort of grand particle accelerator. Sound correct, or am I totally in the toilet?

 

[malawi_glenn]

Why? Was I that wrong? Or did I just not word it right?

What I was saying is that nuclear fusion reactions can be self-sustaining using any fuel with nuclei less than the mass of iron. Nuclear fusion using elements heavier than iron can take place, but will not be self-sustaining because they actually require that energy be input. I think the terminology is that stars fuse elements exothermically (I said endo- in the other post incorrectly), and releasing energy. So stars with iron fuel cannot keep generating energy by creating elements heavier than iron.

When a star goes supernova, some of the material is slammed into other material at energies great enough to cause elements heavier than iron to form. A sort of grand particle accelerator. Sound correct, or am I totally in the toilet?

Yes it is correct, but now maybe even the OP can understand it :-)

 

[dangerbird]

so is the whole idea that stars fuse only up to iron during their lifetimes backed up by stellar spectra observations? Or does that idea only come from the fact that anything heavier than irons not a self sustaning reaction.

 

[malawi_glenn]

so is the whole idea that stars fuse only up to iron during their lifetimes backed up by solar spectra observations? Or does that idea only come from the fact that anything heavier than iron wouldn't be a self sustaning reaction.

(*sigh*) STELLAR spectra observations and of course nuclear theory, there is no such thing as "pure observation" and "pure theory" -> things always goes and in hand.

So the story goes as follows: lead is the end-point of self sustaining thermonuclear reactions, theory statement. YET observations showed that stars DO contain heavier elements, and also elements heavier than Iron was found here on Earth so.. So it was then realized that there are more mechanisms of element generation in stars, namely the s-process. And also one realized that one can have the r-process in supernovae. So one now had more theories, and those also made some sense! Of course, there are still some small unsolved problems but in total we have clear understanding on how the elements are formed in stars, it is a fine precision and delicate science.

Expert litterature:
https://www.amazon.com/dp/3527406026/?tag=pfamazon01-20
https://www.amazon.com/dp/0226724573/?tag=pfamazon01-20

Have fun

 

[Chronos]

Actually, nickel is currently believed to be the heaviest element that can be formed end of the fusion cycle in ordinary stars. See
http://helios.gsfc.nasa.gov/nucleo.html, and
http://en.wikipedia.org/wiki/Silicon_burning_process
Nucleosynthesis cannot account for elements heavier than Ni56 by current theories. The process would actually consume more energy than it produces, as already noted. Note also that once a star starts burning silicon, it is on its last legs. This process can only be sustained for a very short time before core collapse occurs.

 

[malawi_glenn]

Yes, but in almost all introductory exposures, Iron is the element being mentioned.

But as we already have discussed here, heavier elements can be synthesized in stars, via the s-process..

 

[dangerbird]

http://physicsworld.com/cws/article/news/2727
perhaps the folks here haven't heard of the s process even though it was figured out 50 years ago. They say one of the current questions in the universe is "How were the elements from iron to uranium made?" theyre physicists though. that's the thing with physics there's so much confusion about facts. what is known and how is all mixed up one persons says this another says that etc..

 

[dangerbird]

maybe those physicists feel like the s-process wouldn't produce enough. it seems like the sprocess would be very slow and not yield much mass to explain all the elements. its hard to immagine all the elements forming one atom at a time through neutron capture, especially since it has to take place after iron forms which is near the end of a stars life. so there's a brief period after the iron cores formed - supernova where a very slow process can produce all the heavier elements. is it mathematically proven to be a fast enough process to account for the amount of elements which are formed?by amount i mean mass

 

[malawi_glenn]

It's the same in all experimental sciences, but the s- and r-process etc. are very known things in both astrophysics and nuclear physics. There are several other mechanisms as well. I have no idea why they but that issue on their list... LOL sure there are some small anomalies, but those are really really minor.

(I told you about the r-process... so why have you not taken it to you yet?)

If you don't want to buy a book on nuclear physics or nuclear astrophysics (Cauldrons in the Cosmos is really cheap and good though) you can read the following wiki articles:
http://en.wikipedia.org/wiki/Nucleosynthesis
http://en.wikipedia.org/wiki/S-process
http://en.wikipedia.org/wiki/R-process
http://en.wikipedia.org/wiki/P-process

physicists does not "feel" things, one calculates things... otherwise it would not be science but religion or similar :P

yes there have been done extensive simulations and they are fairly accurate.. actually, I have done simulations myself

you should not worry... I get the impression that you are underestimating how powerful modern physics is

 

[dangerbird]

http://en.wikipedia.org/wiki/S-process
"Because of the relatively low neutron fluxes expected to occur during the S-process (on the order of 105 to 1011 neutrons per cm2 per second), this process does not have the ability to produce any of the heavy radioactive isotopes such as Thorium or Uranium. "

so if this process doesn't explain elements heavier than bismuth is it the r-process which does the rest alone? i think that the physicists probably meant to put on the list how heavier elements than bismuth were created since the s-process doesn't do those. it seems like the r-process wouldn't be able to account for all the heavier elements because of the rapid expanding supernova debris would cool as it expands. cool too fast for enough fusion of heavier elements to take place

 

[dangerbird]

http://www.nscl.msu.edu/science/nuclearastrophysics/rprocess
heres another page that's saying the making of heaviest elements is still a mystery.
it seems like this is still a mystery malawi but not a total mystery like youre saying

 

[malawi_glenn]

http://www.nscl.msu.edu/science/nuclearastrophysics/rprocess
heres another page that's saying the making of heaviest elements is still a mystery.
it seems like this is still a mystery malawi but not a total mystery like youre saying

I mean it depends on what level of accuracy you are after and how many of the elements you want to describe. Of course there is a lot of things yet to discover, but the expression "making the elements heavier than Iron is a mystery" can be quantified further as one did on the page you just referred to. The lack of understanding and failure can also be due to incorrect input nuclear data, that is why one needs to do high precision experiments of these very short lived intermediate state nuclei to improve the input data to the models.

But it is clearly a difference in stating "making the elements heavier than Iron is a mystery" and "making of Isotope XYZ is a mystery". When I say it is not a mystery, I am referring to the first statement, that it is false. And then I told you about these minor anomalies, which are isotope specific.

And statements as "we don't know where in the universe this process occurs" means that we have many candidates and several models etc but needs more. This why one can become confused, that one quite often uses a simplified language in popular descriptions of a field, statements which very often are left without references and figures.

Also these descriptions of research activities are often over-exaggerated in order to make it sound more interesting and important :-)
(c.f. with the Higgs boson conquest -> "we don't know where the particles masses comes from".. but there are several theories and ways to find answers, and also one KNOW that 98% of the mass are from the strong interaction, what the Higgs boson does is that it gives mass to the W and Z bosons and the leptons and quarks, thus the popular description above is very over-exaggerated and sounds like we have NO CLUE)

 

[DecayProduct]

I know nothing of the calculations involved in these theories, I'm not there yet. But what is the mass of the core of a collapsing star (going supernova)? What is the predicted amount of uranium and other super heavy elements on our own solar system? What I'm driving at is that the total amount of energy involved, under the conditions inside the cores of such stars, during the time frames involved, even the smallest rates of neutron capture would produce huge (relatively speaking) amounts of the heavy stuff.

Also, it seems like those articles spoke of neutron capture or proton capture, but surely heavy nuclei are colliding with other nuclei. What is the outcome of such events? I know here on Earth we have slammed gold nuclei into tungsten targets and had some pretty heavy elements result from it.

 

[flatmaster]

Semi-emperical mass formula
s-process
r-process
That's all folks

 

[Chronos]

The abundance of nickel in our own solar system indicates it is readily produced by ordinary stellar fusion processes. The scarcity of heavier elements indicates extraordinary processes are necessary for their production [e.g., supernova].

 

[chemisttree]

Read the B²FH paper http://prola.aps.org/pdf/RMP/v29/i4/p547_1"

 

[anonymoussome]

The ordinary stars would generally not form elements heavier than iron. It is because Iron is the most stable (in terms of binding energies) in the whole periodic table. So if we were to analyse the spectra of a normal star it wouldn't show heavy elements. Every heavier element and also the lighter element than iron tend to achieve the iron like state for maximum stability. So for a star to fuse iron into some heavier element, it would require energy. This energy is generated during a supernova when all the fusions take place.

 

[dangerbird]

Speculation and confusion makes me frustrated...

 

[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.