APOD: Where Your Elements Came From (2017 Oct 24)

Comments and questions about the APOD on the main view screen.
Kon Jek Toor

Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby Kon Jek Toor » Wed Oct 25, 2017 5:43 pm

neufer wrote:
MemyselfandI wrote:
Where did the matter come from in the first place?
https://en.wikipedia.org/wiki/A_Universe_from_Nothing wrote:
<<A Universe from Nothing: Why There Is Something Rather than Nothing is a non-fiction book by the physicist Lawrence M. Krauss, initially published on January 10, 2012 by Free Press. It discusses modern cosmogony and its implications for the debate about the existence of God. The main theme of the book is how "we have discovered that all signs suggest a universe that could and plausibly did arise from a deeper nothing—involving the absence of space itself and— which may one day return to nothing via processes that may not only be comprehensible but also processes that do not require any external control or direction.">>



"But this is nothing more than preposterous scientific blashphemy!!!" Signed .. the Consensus

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby ems57fcva » Wed Oct 25, 2017 6:49 pm

Ann wrote:
ems57fcva wrote:Are you all sure that the colors are labeled properly? It shows low-mass stars contributing to everything between Strontium and Lead, while the exploding massive stars are only credited for elements as heavy as Zirconium. That does not look right. I thought that it took a stellar explosion to create elements heavier than iron. And even just a switch of the yellow and green still raises questions in that regard, as the yellow also extends past iron, but the exploding white dwarfs (white) do not.


I remember seeing a Hubble (or Chandra?) picture of a supernova remnant, and the caption said that we can be sure that this is the remnant of a massive star and its core collapse. And the reason why we can be sure of that is that the remnant contains so much oxygen, and oxygen is produced in core-collapse supernovas. And indeed, today's chart says that oxygen is produced almost exclusively by such supernovas.

I also remember reading about red giants and all the chemical processes that go on in them before they shed their outer layers altogether and turn into planetary nebulas and white dwarfs. The text where I read about that said that many elements are created here because neutrons are incorporated into the nuclei of other elements.

If you check out the chart, the "green" elements (green because they were created by low-mass stars) seem kind of weird. There are few well-known elements among them, apart from lithium, carbon and nitrogen, and the highly poisonous elements mercury and lead.

Fascinatingly, though, some silver and even some gold is apparently made by dying red giants!

Ann


As I understand it, dying small stars lack the needed temperatures and pressures to create anything even as heavy as iron; and their planetary nebulas will be full of oxygen (which is not to say that supernovae do not produce a lot of oxygen themselves). In fact, in that other APOD that I referenced, Sulfur was as heavy an element as small stars could create. However, this arrangement seems to come from the LIGO-VIRGO collaboration or someone close to it. See http://growth.caltech.edu/images/gw170817/periodic-table.jpg, which is associated with http://growth.caltech.edu/news-gw170817.html. If this is a mistake, it was made by someone who should have known better.

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby MarkBour » Wed Oct 25, 2017 7:47 pm

I was thinking about what texture patterns would be nice mnemonics for this chart that would be helpful to the color-blind, and had a thought that I probably shouldn't put in print.

I don't think we need Manganese all that badly. Exploding white dwarfs is an extremely cruel practice. Let's demand that it be stopped.
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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby BDanielMayfield » Wed Oct 25, 2017 10:33 pm

ems57fcva wrote:
Ann wrote:
ems57fcva wrote:Are you all sure that the colors are labeled properly? It shows low-mass stars contributing to everything between Strontium and Lead, while the exploding massive stars are only credited for elements as heavy as Zirconium. That does not look right. I thought that it took a stellar explosion to create elements heavier than iron. And even just a switch of the yellow and green still raises questions in that regard, as the yellow also extends past iron, but the exploding white dwarfs (white) do not.


I remember seeing a Hubble (or Chandra?) picture of a supernova remnant, and the caption said that we can be sure that this is the remnant of a massive star and its core collapse. And the reason why we can be sure of that is that the remnant contains so much oxygen, and oxygen is produced in core-collapse supernovas. And indeed, today's chart says that oxygen is produced almost exclusively by such supernovas.

I also remember reading about red giants and all the chemical processes that go on in them before they shed their outer layers altogether and turn into planetary nebulas and white dwarfs. The text where I read about that said that many elements are created here because neutrons are incorporated into the nuclei of other elements.

If you check out the chart, the "green" elements (green because they were created by low-mass stars) seem kind of weird. There are few well-known elements among them, apart from lithium, carbon and nitrogen, and the highly poisonous elements mercury and lead.

Fascinatingly, though, some silver and even some gold is apparently made by dying red giants!

Ann


As I understand it, dying small stars lack the needed temperatures and pressures to create anything even as heavy as iron; and their planetary nebulas will be full of oxygen (which is not to say that supernovae do not produce a lot of oxygen themselves). In fact, in that other APOD that I referenced, Sulfur was as heavy an element as small stars could create. However, this arrangement seems to come from the LIGO-VIRGO collaboration or someone close to it. See http://growth.caltech.edu/images/gw170817/periodic-table.jpg, which is associated with http://growth.caltech.edu/news-gw170817.html. If this is a mistake, it was made by someone who should have known better.


I agree with your questions and observations. The green “dying low mass stars” contribution spread deep into the heavy elements region of this table seems wrong, but perhaps there’s an explanation. The only things I can think of is if there is an explosive transition from a low mass white dwarf into a denser neutron star or even a total stellar disruption event. This loudly begs for a clearer explanation.

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby BDanielMayfield » Wed Oct 25, 2017 11:22 pm

And here’s the explanation, I believe, from the Wikipedia article on Supernova:

Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a degenerate star or the sudden gravitational collapse of a massive star's core. In the first instance, a degenerate white dwarf may accumulate sufficient material from a binary companion, either through accretion or via a merger, to raise its core temperature enough to trigger runaway nuclear fusion, completely disrupting the star. In the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy as a supernova. While some observed supernovae are more complex than these two simplified theories, the astrophysical collapse mechanics have been established and accepted by most astronomers for some time.


This must be what is meant by “dying low mass star”, the detonation of a white dwarf.

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby BDanielMayfield » Wed Oct 25, 2017 11:40 pm

BDanielMayfield wrote:And here’s the explanation, I believe, from the Wikipedia article on Supernova:

Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a degenerate star or the sudden gravitational collapse of a massive star's core. In the first instance, a degenerate white dwarf may accumulate sufficient material from a binary companion, either through accretion or via a merger, to raise its core temperature enough to trigger runaway nuclear fusion, completely disrupting the star. In the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy as a supernova. While some observed supernovae are more complex than these two simplified theories, the astrophysical collapse mechanics have been established and accepted by most astronomers for some time.


This must be what is meant by “dying low mass star”, the detonation of a white dwarf.

Bruce


Scratch that. Looking at the table again, I see that there is already a white or grey code for the contribution from Exploding White Dwarf Stars, so the mystery remains unsolved.
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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby MemyselfandI » Thu Oct 26, 2017 8:22 am

neufer wrote:
MemyselfandI wrote:
Where did the matter come from in the first place?
https://en.wikipedia.org/wiki/A_Universe_from_Nothing wrote:
<<A Universe from Nothing: Why There Is Something Rather than Nothing is a non-fiction book by the physicist Lawrence M. Krauss, initially published on January 10, 2012 by Free Press. It discusses modern cosmogony and its implications for the debate about the existence of God. The main theme of the book is how "we have discovered that all signs suggest a universe that could and plausibly did arise from a deeper nothing—involving the absence of space itself and— which may one day return to nothing via processes that may not only be comprehensible but also processes that do not require any external control or direction.">>


The words, "suggest, plausibly, may" do not explain an answer, they merely point to one theory, probably (sic) among many. The original post was rather more definite, "Where your elements came from." My question was, where did the matter come from in the first place? An ex nihilo postulation only makes rational sense if one can argue for something (or someone) to create from nothing.

From the Wikipaedia article cited (https://en.wikipedia.org/wiki/A_Universe_from_Nothing):
"In the New York Times, philosopher of science and physicist David Albert said the book failed to live up to its title; he claimed Krauss dismissed concerns about what Albert calls his misuse of the term nothing.[7]

"Commenting on the philosophical debate sparked by the book, the physicist Sean M. Carroll asked, "Do advances in modern physics and cosmology help us address these underlying questions, of why there is something called the universe at all, and why there are things called 'the laws of physics,' and why those laws seem to take the form of quantum mechanics, and why some particular wave function and Hamiltonian? In a word: no. I don't see how they could."[8]

"Science journalist John Horgan, writing for Scientific American, characterizes the book as "...a pop-science book that recycles a bunch of stale ideas from physics and cosmology." [9]

"Physicist George F. R. Ellis characterized the book's thesis as "...presenting untested speculative theories of how things came into existence...". Referring to the entities Krauss assumes to exist, Ellis says "He does not explain in what way these entities could have pre-existed the coming into being of the universe, why they should have existed at all, or why they should have had the form they did. And he gives no experimental or observational process whereby we could test these vivid speculations of the supposed universe-generation mechanism. How indeed can you test what existed before the universe existed? You can’t. Thus what he is presenting is not tested science." [10]

"The mathematical physicist I. S. Kohli also analyzed the main technical arguments in Krauss' book, concluding that "many of the claims are not supported in full by modern general relativity theory or quantum field theory in curved spacetime".[11]"

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby BDanielMayfield » Thu Oct 26, 2017 12:54 pm

MemyselfandI wrote:Where did the matter come from in the first place?


From energy. E=mc2, so therefore m=E/c2.

The next logical questions are:
    Where did the energy come from?
    Where did the laws come from that govern that energy?

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby Chris Peterson » Thu Oct 26, 2017 2:00 pm

MemyselfandI wrote:My question was, where did the matter come from in the first place? An ex nihilo postulation only makes rational sense if one can argue for something (or someone) to create from nothing.

There is no good reason to assume that something can't come from nothing, nor to assume that effects require causes. The best answer we currently have to the origin of the Universe is that it came from nothing and had no cause. That is the answer most consistent with our understanding of physics.
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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby BDanielMayfield » Thu Oct 26, 2017 2:13 pm

Chris Peterson wrote:
MemyselfandI wrote:My question was, where did the matter come from in the first place? An ex nihilo postulation only makes rational sense if one can argue for something (or someone) to create from nothing.

There is no good reason to assume that something can't come from nothing, nor to assume that effects require causes. The best answer we currently have to the origin of the Universe is that it came from nothing and had no cause. That is the answer most consistent with our understanding of physics.

Stepped in what? “There is no good reason to assume that something can’t come from nothing,” How about human experience in which we never see an effect that didn’t also have a cause?

Bruce
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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby Chris Peterson » Thu Oct 26, 2017 2:29 pm

BDanielMayfield wrote:
Chris Peterson wrote:
MemyselfandI wrote:My question was, where did the matter come from in the first place? An ex nihilo postulation only makes rational sense if one can argue for something (or someone) to create from nothing.

There is no good reason to assume that something can't come from nothing, nor to assume that effects require causes. The best answer we currently have to the origin of the Universe is that it came from nothing and had no cause. That is the answer most consistent with our understanding of physics.

Stepped in what? “There is no good reason to assume that something can’t come from nothing,” How about human experience in which we never see a cause that didn’t also have an effect?

That is the worst possible reason. A logical fallacy of the highest order. I call it the Billiard Ball Fallacy: the belief that the Universe must work across all its scales in the same way that we evolved to sense and understand the tiny little bit we can see.

In fact, when we look beyond our primary senses, we do see things without cause (e.g. particle decay) and things that come from nothing (e.g. virtual particles). The Universe is apparently quite comfortable with these concepts.
Chris

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby neufer » Thu Oct 26, 2017 2:46 pm

BDanielMayfield wrote:
Chris Peterson wrote:
MemyselfandI wrote:
My question was, where did the matter come from in the first place? An ex nihilo postulation only makes rational sense if one can argue for something (or someone) to create from nothing.

There is no good reason to assume that something can't come from nothing, nor to assume that effects require causes. The best answer we currently have to the origin of the Universe is that it came from nothing and had no cause. That is the answer most consistent with our understanding of physics.

Stepped in what? “There is no good reason to assume that something can’t come from nothing,” How about human experience in which we never see an effect that didn’t also have a cause?

https://en.wikipedia.org/wiki/Unmoved_mover#First_cause wrote:
<<In book VIII of his Physics, Aristotle examines the notions of change or motion, and attempts to show by a challenging argument, that the mere supposition of a 'before' and an 'after', requires a first principle. He argues that in the beginning, if the cosmos had come to be, its first motion would lack an antecedent state, and as Parmenides said, "nothing comes from nothing". The Cosmological argument, later attributed to Aristotle, thereby draws the conclusion that God exists. However, if the cosmos had a beginning, Aristotle argued, it would require an efficient first cause, a notion that Aristotle took to demonstrate a critical flaw. The purpose of Aristotle's cosmological argument, that at least one eternal unmoved mover must exist, is to support everyday change.>>
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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby BDanielMayfield » Thu Oct 26, 2017 3:31 pm

Chris Peterson wrote:
BDanielMayfield wrote:“There is no good reason to assume that something can’t come from nothing,” How about human experience in which we never see a cause an effect that didn’t also have an effect a cause?

That is the worst possible reason. A logical fallacy of the highest order. I call it the Billiard Ball Fallacy: the belief that the Universe must work across all its scales in the same way that we evolved to sense and understand the tiny little bit we can see.

In fact, when we look beyond our primary senses, we do see things without cause (e.g. particle decay) and things that come from nothing (e.g. virtual particles). The Universe is apparently quite comfortable with these concepts.


One can call black white or vice versa but it doesn’t make it so, just as one can call common sense “a logical fallacy of the highest order.”

Partical decay is without cause? The timing of one particle’s decay is unpredictable, but reason for (or in other words, cause of) its decay are laws governing the behavior of subatomic particles. I would also argue that virtual particles are coming from something that caused them to come into existence.

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby Chris Peterson » Thu Oct 26, 2017 4:13 pm

BDanielMayfield wrote:
Chris Peterson wrote:
BDanielMayfield wrote:“There is no good reason to assume that something can’t come from nothing,” How about human experience in which we never see a cause an effect that didn’t also have an effect a cause?

That is the worst possible reason. A logical fallacy of the highest order. I call it the Billiard Ball Fallacy: the belief that the Universe must work across all its scales in the same way that we evolved to sense and understand the tiny little bit we can see.

In fact, when we look beyond our primary senses, we do see things without cause (e.g. particle decay) and things that come from nothing (e.g. virtual particles). The Universe is apparently quite comfortable with these concepts.


One can call black white or vice versa but it doesn’t make it so, just as one can call common sense “a logical fallacy of the highest order.”

Indeed, in most contexts, invoking common sense most certainly is a logical fallacy.

Partical decay is without cause? The timing of one particle’s decay is unpredictable, but reason for (or in other words, cause of) its decay are laws governing the behavior of subatomic particles.

The fact that we can apply a statistical rule to something does not create a cause. The fact is, nobody has been able to identify a cause for particle decay. The event happens, but no precipitating factor appears to exist.

I would also argue that virtual particles are coming from something that caused them to come into existence.

You may argue that all you want, but it doesn't change our physical understanding of the process, which is that there is neither a cause, nor a "something" that they came from.
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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby jajohnson51 » Thu Oct 26, 2017 6:26 pm

ems57fcva wrote:
Ann wrote:
ems57fcva wrote:Are you all sure that the colors are labeled properly? It shows low-mass stars contributing to everything between Strontium and Lead, while the exploding massive stars are only credited for elements as heavy as Zirconium. That does not look right. I thought that it took a stellar explosion to create elements heavier than iron. And even just a switch of the yellow and green still raises questions in that regard, as the yellow also extends past iron, but the exploding white dwarfs (white) do not.


I remember seeing a Hubble (or Chandra?) picture of a supernova remnant, and the caption said that we can be sure that this is the remnant of a massive star and its core collapse. And the reason why we can be sure of that is that the remnant contains so much oxygen, and oxygen is produced in core-collapse supernovas. And indeed, today's chart says that oxygen is produced almost exclusively by such supernovas.

I also remember reading about red giants and all the chemical processes that go on in them before they shed their outer layers altogether and turn into planetary nebulas and white dwarfs. The text where I read about that said that many elements are created here because neutrons are incorporated into the nuclei of other elements.

If you check out the chart, the "green" elements (green because they were created by low-mass stars) seem kind of weird. There are few well-known elements among them, apart from lithium, carbon and nitrogen, and the highly poisonous elements mercury and lead.

Fascinatingly, though, some silver and even some gold is apparently made by dying red giants!

Ann


As I understand it, dying small stars lack the needed temperatures and pressures to create anything even as heavy as iron; and their planetary nebulas will be full of oxygen (which is not to say that supernovae do not produce a lot of oxygen themselves). In fact, in that other APOD that I referenced, Sulfur was as heavy an element as small stars could create. However, this arrangement seems to come from the LIGO-VIRGO collaboration or someone close to it. See http://growth.caltech.edu/images/gw170817/periodic-table.jpg, which is associated with http://growth.caltech.edu/news-gw170817.html. If this is a mistake, it was made by someone who should have known better.


One of the people who put the graphic together here. The heavy elements (=beyond the iron peak) are made by capturing neutrons onto "seed" nuclei, such as iron. Neutron capture is needed because the electric repulsion between a nucleus like iron (26 protons) and an additional proton is very strong, but between a neutron and an iron nucleus there is none. Dying low-mass stars can make heavier elements not because they reach very high temperatures, like those needed to fuse silicon towards iron, but because nuclear reactions happen in these stars that create free neutrons. These neutrons can then be captured by iron (for example) nuclei that are in the star not because they were formed in the star but because those seed nuclei were in the gas out of which the star was born. The Sun has iron nuclei in it for this reason.

These neutron-capture reactions are not important for creating energy in the star, so when we discuss nuclear fusion in stars, this process is rarely mentioned. For the origin of the elements it matters! And it has been spectacularly demonstrated to be correct, as we have seen newly-minted technetium in these dying low-mass stars. Because the longest-lived technetium isotope has a half-life of 4.2 million years, much, much shorter than the lives of these stars, any technetium in these stars must be made there, rather than being in the natal gas.

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby MarkBour » Thu Oct 26, 2017 7:21 pm

jajohnson51 wrote: One of the people who put the graphic together here ...

Thanks for your reply, Dr. Johnson. You focused on Technetium, I think because it is a tell-tale element that had to have been created there, and indeed created near the end of the star's life. But I gather then that most anything else from Iron on up to Technetium and probably a ways beyond is made by this same process. Thanks to your naming of the process, I'm led to a Wikipedia article on it:
https://en.wikipedia.org/wiki/Neutron_capture
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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby terpsucka » Thu Oct 26, 2017 8:26 pm

BDanielMayfield wrote:
BDanielMayfield wrote:And here’s the explanation, I believe, from the Wikipedia article on Supernova:

Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a degenerate star or the sudden gravitational collapse of a massive star's core. In the first instance, a degenerate white dwarf may accumulate sufficient material from a binary companion, either through accretion or via a merger, to raise its core temperature enough to trigger runaway nuclear fusion, completely disrupting the star. In the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy as a supernova. While some observed supernovae are more complex than these two simplified theories, the astrophysical collapse mechanics have been established and accepted by most astronomers for some time.


This must be what is meant by “dying low mass star”, the detonation of a white dwarf.

Bruce


Scratch that. Looking at the table again, I see that there is already a white or grey code for the contribution from Exploding White Dwarf Stars, so the mystery remains unsolved.


I came here looking for the answer to this question as well. In fact, I've found references to this and similar periodic table efforts, with some level of explanation for every grouping except for this one!

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby MarkBour » Thu Oct 26, 2017 8:54 pm

terpsucka wrote: ...
I came here looking for the answer to this question as well. In fact, I've found references to this and similar periodic table efforts, with some level of explanation for every grouping except for this one!

So, did the post just above, from jajohnson51, help?
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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby terpsucka » Thu Oct 26, 2017 9:16 pm

MarkBour wrote:
terpsucka wrote: ...
I came here looking for the answer to this question as well. In fact, I've found references to this and similar periodic table efforts, with some level of explanation for every grouping except for this one!

So, did the post just above, from jajohnson51, help?


They sure do! Thanks!!

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby terpsucka » Thu Oct 26, 2017 9:21 pm

jajohnson51 wrote:
ems57fcva wrote:
Ann wrote:
I remember seeing a Hubble (or Chandra?) picture of a supernova remnant, and the caption said that we can be sure that this is the remnant of a massive star and its core collapse. And the reason why we can be sure of that is that the remnant contains so much oxygen, and oxygen is produced in core-collapse supernovas. And indeed, today's chart says that oxygen is produced almost exclusively by such supernovas.

I also remember reading about red giants and all the chemical processes that go on in them before they shed their outer layers altogether and turn into planetary nebulas and white dwarfs. The text where I read about that said that many elements are created here because neutrons are incorporated into the nuclei of other elements.

If you check out the chart, the "green" elements (green because they were created by low-mass stars) seem kind of weird. There are few well-known elements among them, apart from lithium, carbon and nitrogen, and the highly poisonous elements mercury and lead.

Fascinatingly, though, some silver and even some gold is apparently made by dying red giants!

Ann


As I understand it, dying small stars lack the needed temperatures and pressures to create anything even as heavy as iron; and their planetary nebulas will be full of oxygen (which is not to say that supernovae do not produce a lot of oxygen themselves). In fact, in that other APOD that I referenced, Sulfur was as heavy an element as small stars could create. However, this arrangement seems to come from the LIGO-VIRGO collaboration or someone close to it. See http://growth.caltech.edu/images/gw170817/periodic-table.jpg, which is associated with http://growth.caltech.edu/news-gw170817.html. If this is a mistake, it was made by someone who should have known better.


One of the people who put the graphic together here. The heavy elements (=beyond the iron peak) are made by capturing neutrons onto "seed" nuclei, such as iron. Neutron capture is needed because the electric repulsion between a nucleus like iron (26 protons) and an additional proton is very strong, but between a neutron and an iron nucleus there is none. Dying low-mass stars can make heavier elements not because they reach very high temperatures, like those needed to fuse silicon towards iron, but because nuclear reactions happen in these stars that create free neutrons. These neutrons can then be captured by iron (for example) nuclei that are in the star not because they were formed in the star but because those seed nuclei were in the gas out of which the star was born. The Sun has iron nuclei in it for this reason.

These neutron-capture reactions are not important for creating energy in the star, so when we discuss nuclear fusion in stars, this process is rarely mentioned. For the origin of the elements it matters! And it has been spectacularly demonstrated to be correct, as we have seen newly-minted technetium in these dying low-mass stars. Because the longest-lived technetium isotope has a half-life of 4.2 million years, much, much shorter than the lives of these stars, any technetium in these stars must be made there, rather than being in the natal gas.


Thank you Dr Johnson for your help in understanding this process, and your work on this excellent graphic!!

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby BDanielMayfield » Fri Oct 27, 2017 1:10 am

jajohnson51 wrote:One of the people who put the graphic together here. The heavy elements (=beyond the iron peak) are made by capturing neutrons onto "seed" nuclei, such as iron. Neutron capture is needed because the electric repulsion between a nucleus like iron (26 protons) and an additional proton is very strong, but between a neutron and an iron nucleus there is none. Dying low-mass stars can make heavier elements not because they reach very high temperatures, like those needed to fuse silicon towards iron, but because nuclear reactions happen in these stars that create free neutrons. These neutrons can then be captured by iron (for example) nuclei that are in the star not because they were formed in the star but because those seed nuclei were in the gas out of which the star was born. The Sun has iron nuclei in it for this reason.

These neutron-capture reactions are not important for creating energy in the star, so when we discuss nuclear fusion in stars, this process is rarely mentioned. For the origin of the elements it matters! And it has been spectacularly demonstrated to be correct, as we have seen newly-minted technetium in these dying low-mass stars. Because the longest-lived technetium isotope has a half-life of 4.2 million years, much, much shorter than the lives of these stars, any technetium in these stars must be made there, rather than being in the natal gas.


Thank you so much for clearing this up for us. Of course, each answer often leads to further questions. Can you point us to papers and/or articles that give more details re this dying low-mass star heavy element production pathway?

Bruce
"Happy are the peaceable ... "

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby BDanielMayfield » Fri Oct 27, 2017 8:28 pm

With the aid of jajohnson’s, Ann’s and MarkBour’s comments I’ve been given enough clues to find the info I wanted. It’s in the Wikipedia article on s-process, for slow neutron capture:

The slow neutron capture process or s-process is a series of reactions in nuclear astrophysics which occur in stars, particularly AGB stars. The s-process is responsible for the creation (nucleosynthesis) of approximately half the atomic nuclei heavier than iron.

In the s-process, a seed nucleus undergoes neutron capture to form an isotope with one higher atomic mass. If the new isotope is stable a series of increases in mass can occur, but if it is unstable then beta decay will occur, producing an element of the next highest atomic number. The process is slow (hence the name) in the sense that there is sufficient time for this radioactive decay to occur before another neutron is captured. A series of these reactions produces stable isotopes by moving along the valley of beta-decay stable isobars in the chart of isotopes.

A range of elements and isotopes can be produced by the s-process, because of the intervention of alpha decay steps along the reaction chain. The relative abundances of elements and isotopes produced depends on the source of the neutrons and how their flux changes over time. Each branch of the s-process reaction chain eventually terminates at a cycle involving lead, bismuth, and polonium.

The s-process contrasts with the r-process, in which successive neutron captures are rapid: they happen more quickly than the beta decay can occur. The r-process dominates in environments which have a higher flux of free neutrons; it produces heavier elements and more neutron-rich isotopes than the s-process. Together the two processes account for the majority of abundance evolution of elements heavier than iron.

...

The s-process is believed to occur mostly in asymptotic giant branch stars, seeded by iron nuclei left by a supernova during a previous generation of stars. In contrast to the r-process which is believed to occur over time scales of seconds in explosive environments, the s-process is believed to occur over time scales of thousands of years, passing decades between neutron captures. The extent to which the s-process moves up the elements in the chart of isotopes to higher mass numbers is essentially determined by the degree to which the star in question is able to produce neutrons. The quantitative yield is also proportional to the amount of iron in the star's initial abundance distribution. Iron is the "starting material" (or seed) for this neutron capture – beta-minus decay sequence of synthesizing new elements.


The article went on to state that the two main neutron source reactions are C13+He4->O16+n and Ne22+He4->Mg25+n.

Therefor only stars massive enough to fuse carbon and helium into oxygen can start the s-process.

Also, Mark, have you taken in any Magnesium today? All life as we know it needs it, and it helps stars crank out heavy elements to boot. :wink:

Bruce
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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby neufer » Fri Oct 27, 2017 9:49 pm

BDanielMayfield wrote:
Also, Mark, have you taken in any Magnesium today?

All life as we know it needs it, and it helps stars crank out heavy elements to boot. :wink:

Bruce
https://en.wikipedia.org/wiki/Brucite wrote:
<<Brucite is the mineral form of magnesium hydroxide: Mg(OH)2. Magnesium hydroxide is a common component of antacids, such as milk of magnesia, as well as laxatives. Brucite was first described in 1824 and named for the discoverer, American mineralogist, Archibald Bruce (1777–1818). It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites. Brucite is often found in association with serpentine, calcite, aragonite, dolomite, magnesite, hydromagnesite, artinite, talc and chrysotile.>>
Art Neuendorffer

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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby BDanielMayfield » Fri Oct 27, 2017 11:35 pm

neufer wrote:
BDanielMayfield wrote:
Also, Mark, have you taken in any Magnesium today?

All life as we know it needs it, and it helps stars crank out heavy elements to boot. :wink:

Bruce
https://en.wikipedia.org/wiki/Brucite wrote:
<<Brucite is the mineral form of magnesium hydroxide: Mg(OH)2. Magnesium hydroxide is a common component of antacids, such as milk of magnesia, as well as laxatives. Brucite was first described in 1824 and named for the discoverer, American mineralogist, Archibald Bruce (1777–1818). It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites. Brucite is often found in association with serpentine, calcite, aragonite, dolomite, magnesite, hydromagnesite, artinite, talc and chrysotile.>>


I’ve often wondered how I received the name Bruce. My dad’s youngest sibling was named Daniel, but no relatives on either side of my family tree are known to have been named Bruce. Mom simply said she liked it. I think the rather unusual label helped toughen my skin a little, which could have contributed to my rather non-conformist, contrarian personally. (For a more extreme but fictional example of this phenomena please see Johnny Cash’s hit song A boy named Sue.)

Back to the much more interesting nucleosynthesis, futher reading has informed me that of the two neutron sources for the S-process, only the one starting with Carbon 13 is the source for low mass stellar fusion of heavy elements. The S-process pathway involving magnesium only happens in high mass stars destined to blow up as core collapse supernovae.

Bruce
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Re: APOD: Where Your Elements Came From (2017 Oct 24)

Postby MarkBour » Sat Oct 28, 2017 7:57 pm

BDanielMayfield wrote:Also, Mark, have you taken in any Magnesium today? All life as we know it needs it, and it helps stars crank out heavy elements to boot. :wink:
Bruce

Thanks for the dietary reminder, Bruce. I probably haven't had enough. I'd better go eat some nuts and bananas.
Mark Goldfain


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