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Bhim

Supernovae may not be the principle source of heavy elements

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Stellar evolution was never among my research interests, so maybe this is no surprise to people in that sub-field. However, for as long as I can remember the common wisdom among astrophysicists has been that while all elements in the universe lighter than (and including) iron are created via nuclear fusion inside stellar interiors, and that elements heavier than iron are produced principally by supernovae. It turns out the second part of this statement might not be true:

 

http://physicstoday.scitation.org/doi/10.1063/PT.3.3815

 

It's a rather lengthy and technical article. To summarize for you guys, let me start out by saying that the creation of the elements in the universe is quite a nontrivial process. Hydrogen, requiring no "production" beyond the creation of protons and electrons, is of course the most ubiquitous element. Everything else has to be produced by nuclear fusion. Helium was produced in the big bang, but pretty much everything else up to iron comes from nuclei fusing with each other inside stars. The reason iron is the barrier is because beyond iron, it becomes energetically unfavorable to produce a heavier element by fusion. The creation of heavier nuclei is possible by neutron capture, where a nucleus absorbs a neutron, becomes an unstable isotope, then decays (usually by beta decay) to produce a heavier, stable element. Efficient neutron capture nucleosynthesis requires a high neutron density, and since this is found in a supernova, it's thought that supernovae are predominantly responsible for the creation of everything in the universe heavier than iron.

 

According to this article though, recent observations of a satellite galaxy of the Milky Way (i.e. a smaller galaxy orbiting our own) suggests this may not be the case. Basically, the chemical composition of this satellite galaxy is not justified by the level of supernova activity we see (galaxies average 2 supernovae per century), and thus it's possible that neutron star mergers may in fact be responsible for the production of heavy elements.

 

Personally, I'm surprised that this isn't making bigger news. Don't get me wrong, Physics Today is not some arcane journal; it's intended for a technically-minded broader audience, and it's certainly a good place for an article like this. But what we have here is a contradiction of what for decades has been common wisdom among astrophysicists. It's not fundamental on the level of gravitation wave or Higgs Boson production. But I recall a few years ago that the discovery of gamma ray lobes in the core of the Milky Way made the New York Times. This seems like the sort of discovery which should break into mainstream press. Seeing as it has not, I figured I'd post it here for your consideration. It's an interesting insight into the origins of many of the commonplace chemicals found in nature on earth.

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I thought there has been a consensus among the relevant astrophysicists, for quite some time, that the heaviest elements were not formed in supernovas, but in stellar events larger than supernovas and in neutron star mergers.

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3 hours ago, sdelsolray said:

I thought there has been a consensus among the relevant astrophysicists, for quite some time, that the heaviest elements were not formed in supernovas, but in stellar events larger than supernovas and in neutron star mergers.

 

Well, in various colloquia I've attended over the years people often mention supernovae in passing as the principle source of heavy elements. Also, this paper cites a statement by Cowan and Thielemann that supernovae do contain the necessary neutron flux to create heavy elements by neutron capture. Indeed, the important result here is that the chemical composition observations of the satellite galaxy rule out supernovae as the principle source. So until this observation, I would guess supernovae were still the favored candidate source of heavy elements.

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On 1/6/2018 at 1:33 PM, Bhim said:

Stellar evolution was never among my research interests, so maybe this is no surprise to people in that sub-field. However, for as long as I can remember the common wisdom among astrophysicists has been that while all elements in the universe lighter than (and including) iron are created via nuclear fusion inside stellar interiors, and that elements heavier than iron are produced principally by supernovae. It turns out the second part of this statement might not be true:

 

http://physicstoday.scitation.org/doi/10.1063/PT.3.3815

 

It's a rather lengthy and technical article. To summarize for you guys, let me start out by saying that the creation of the elements in the universe is quite a nontrivial process. Hydrogen, requiring no "production" beyond the creation of protons and electrons, is of course the most ubiquitous element. Everything else has to be produced by nuclear fusion. Helium was produced in the big bang, but pretty much everything else up to iron comes from nuclei fusing with each other inside stars. The reason iron is the barrier is because beyond iron, it becomes energetically unfavorable to produce a heavier element by fusion. The creation of heavier nuclei is possible by neutron capture, where a nucleus absorbs a neutron, becomes an unstable isotope, then decays (usually by beta decay) to produce a heavier, stable element. Efficient neutron capture nucleosynthesis requires a high neutron density, and since this is found in a supernova, it's thought that supernovae are predominantly responsible for the creation of everything in the universe heavier than iron.

 

According to this article though, recent observations of a satellite galaxy of the Milky Way (i.e. a smaller galaxy orbiting our own) suggests this may not be the case. Basically, the chemical composition of this satellite galaxy is not justified by the level of supernova activity we see (galaxies average 2 supernovae per century), and thus it's possible that neutron star mergers may in fact be responsible for the production of heavy elements.

 

Personally, I'm surprised that this isn't making bigger news. Don't get me wrong, Physics Today is not some arcane journal; it's intended for a technically-minded broader audience, and it's certainly a good place for an article like this. But what we have here is a contradiction of what for decades has been common wisdom among astrophysicists. It's not fundamental on the level of gravitation wave or Higgs Boson production. But I recall a few years ago that the discovery of gamma ray lobes in the core of the Milky Way made the New York Times. This seems like the sort of discovery which should break into mainstream press. Seeing as it has not, I figured I'd post it here for your consideration. It's an interesting insight into the origins of many of the commonplace chemicals found in nature on earth.

 

Hi Bhim,

 

Yeah I also  think that this is a good new theory IMO, but it does not discount supernovae as also being a source of creation for the heaviest elements. As you know

theoretical Neutron stars are supposedly created in the aftermath of supernova explosions and implosions as their cores collapse, with the protons and electrons theoretically merging together. However this may not be the whole story. Some of the heavier nuclei of heavier elements created by the supernova could be carried into the neutron star and end up being on its surface because of the lower density of these nuclei compared to the neutron star. Upon collision with anything, such surface elements might be shaken loose. If this were so then these heavier nuclei would still have been created by the supernova in the first place.  Because of the abundance of heavier elements that we observe here on Earth and probably equally in the solar system, I suspect there is a much more abundant creation mechanism for these elements.  I believe the central black holes of galaxies play a part in this. In any event IMO it shows that we are still a long ways away from having a complete understanding concerning the workings of the cosmos.
 
Happy New Year to you  --  I just submitted our "no dark matter" paper to the Astrophysical Journal this week. I traveled for a couple of months near the end of 2017 so I am  back now and have submitted the paper and now waiting for their response. Thanks again for the reference. cheers :)

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On 1/8/2018 at 11:13 PM, pantheory said:

 

Hi Bhim,

 

Yeah I also  think that this is a good new theory IMO, but it does not discount supernovae as also being a source of creation for the heaviest elements. As you know

theoretical Neutron stars are supposedly created in the aftermath of supernova explosions and implosions as their cores collapse, with the protons and electrons theoretically merging together. However this may not be the whole story. Some of the heavier nuclei of heavier elements created by the supernova could be carried into the neutron star and end up being on its surface because of the lower density of these nuclei compared to the neutron star. Upon collision with anything, such surface elements might be shaken loose. If this were so then these heavier nuclei would still have been created by the supernova in the first place.  Because of the abundance of heavier elements that we observe here on Earth and probably equally in the solar system, I suspect there is a much more abundant creation mechanism for these elements.  I believe the central black holes of galaxies play a part in this. In any event IMO it shows that we are still a long ways away from having a complete understanding concerning the workings of the cosmos.
 
Happy New Year to you  --  I just submitted our "no dark matter" paper to the Astrophysical Journal this week. I traveled for a couple of months near the end of 2017 so I am  back now and have submitted the paper and now waiting for their response. Thanks again for the reference. cheers :)

 

Hi Pantheory, happy New Year to you as well.

 

I'm following everything you said, except for the bit about "collision with anything." Are you referring to accretion of matter onto the post-supernova neutron star by some passing star which becomes a binary companion? Do you suspect that you could probe for these heavier nuclei by measuring the spectra of candidate neutron stars. I realize that may be difficult due to the surrounding supernova remnant which will have swept out a lot of the ISM in most cases, but just a thought.

 

Anyway, good luck on your submission!

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1 hour ago, Bhim said:

 

Hi Pantheory, happy New Year to you as well.

 

I'm following everything you said, except for the bit about "collision with anything." Are you referring to accretion of matter onto the post-supernova neutron star by some passing star which becomes a binary companion? Do you suspect that you could probe for these heavier nuclei by measuring the spectra of candidate neutron stars. I realize that may be difficult due to the surrounding supernova remnant which will have swept out a lot of the ISM in most cases, but just a thought.

 

Anyway, good luck on your submission!

 

Yes, such fully ionized heavy nuclei on the surface of the neutron star would not produce any EM radiation without electrons, but I would suspect that some would be in orbit partly or wholly reionized, and if there were enough of them maybe their spectra might be detectable. Of course when I said "upon collision with anything" I meant collision with a massive star, black hole or other neutron star big enough for a close pass or collision to knock some of these heavy nuclei off the surface of the neutron star if in fact there were any there, and in large enough numbers to be detectable after being blown off the surface. Yes, the supernova would have cleared the surrounding ISM but I would expect that there would be some orbital materials from the explosion and back-fall of plasma and heavy nuclei, between the explosion and implosion.

 

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On ‎09‎/‎01‎/‎2018 at 6:13 PM, pantheory said:
Happy New Year to you  --  I just submitted our "no dark matter" paper to the Astrophysical Journal this week. I traveled for a couple of months near the end of 2017 so I am  back now and have submitted the paper and now waiting for their response. Thanks again for the reference. cheers :)

 

Pantheory - it seems there are a number of papers surrounding 'No dark matter' - this one for instance... unless this one is yours?

 

https://www.sciencedaily.com/releases/2017/11/171122113013.htm

https://phys.org/news/2017-11-dark-energy.html

 

(Two links, same paper, different publications)

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On 1/16/2018 at 4:49 PM, LogicalFallacy said:

 

Pantheory - it seems there are a number of papers surrounding 'No dark matter' - this one for instance... unless this one is yours?

 

https://www.sciencedaily.com/releases/2017/11/171122113013.htm

https://phys.org/news/2017-11-dark-energy.html

 

(Two links, same paper, different publications)

 

Yes, there have been a number of "no dark matter" papers, as well as a number of no dark energy papers. The one you have posted in not my paper.I have written both types of papers but have only got our "no dark energy" paper published. Here is the link to that paper, and second the link to one of the press releases. Both published in 2014.

 

http://www.ccsenet.org/journal/index.php/apr/article/view/32603

http://revolution-green.com/new-research-study-concluded-dark-energy-probably-exist/

 

The "no dark matter" paper has been more difficult to get published. I wrote the first version of the paper in 2015 but couldn't find a well-known scientific publisher willing to publish it at that time. I redid the paper a number of times and also had it criticized many times. I finally have a better version of it now that I submitted just this month, January. It presently seems that it will be accepted in this high impact journal that has many readers, and hopefully many responses to this paper. Upon the formal acceptance of the paper after peer review, I will write a press release and post both on this board for those who may be interested.

 

As to neutron star collisions creating most of the heavy elements in the universe, I think the theory is good but IMO neither neutron stars nor supernovae are the primary producers of the heavy elements in the universe. Right now my proposed alternative mechanism is either too speculation or is a weak hypothesis depending upon whether the idea can be tested or not. If in time I can come up with some feasible way to test this alternative proposal then at that time I expect to write a paper on the possibility. Time will tell.

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