There's Gold in Them Neutron Stars - or - Maybe Not

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Summary:

When humanity finally detected the collision between two neutron stars in 2017, we confirmed a long-held theory - in the energetic fires of these incredible explosions, elements heavier than iron are forged.

But a new analysis has revealed a problem. According to new galactic chemical evolution models, neutron star collisions don't even come close to producing the abundances of heavy elements found in the Milky Way galaxy today.
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  • #2
mathman
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I am under the impression that the heavy elements are produced in supernova explosions.
 
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phinds
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I am under the impression that the heavy elements are produced in supernova explosions.
My understanding is that that was the conventional wisdom for a long time but that recently the view has shifted to their being created mostly by neutron star collision explosions and by supernovae but to a lesser degree (lesser amount of the overall mass produced for each element)
 
  • #5
ORF
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Hi,

there are issues difficult to understand and explain in both sources.

It is claimed that Neutron Star Mergers (NSM) are not the main source of r-process elements because of timing: there are r-process abundance pattern in metal-poor stars in the galactic halo, which are up to 12Gyears old. That means that there was a heavy element source already working between the Big Bang and the moment of formation of those stars. In principle, stars would need more than that to evolve to a neutron star and then collide. The other problem with NSM is the ejection mechanisms: it is not clear that the amount of ejected material is enough to explain everything.

On the other hand, supernova and core-collapse supernova may not reach the conditions to form heavy nuclei by neutron capture (ie, there are not enough neutrons). The current treatment of neutrino in simulations is very simplistic. These neutrinos decrease the neutron density (which is much lower than in NSM) and prevents the formation of the heaviest elements. Only under extreme conditions of high rotation speed and very intense magnetic fields (up to 1e10 - 1e12 T) in very massive stars it is possible to achieve a full r-process in a simulation. The problem here is the number of observations which support the existence of such massive stars...

As far as I know, all of these just rely on simulations.

These are astrophysical sites where r-process may take place. But there are other processes which can synthesize heavy elements, like p-process or s-process. The problem with s-process is that we can not measure at laboratory the reaction rates (the probability of capturing a neutron) for energies which are found in stars. So, one has to invent a model and extrapolate... so, this may be another uncertainty source, which is usually disregarded.

In addition, Galactic Chemical Evolution (GCE) models rely on theoretical/simulated yields which introduce a huge uncertainty, and GCE conclusions may be misleading.

Sorry this post increase the uncertainty instead of answering the OP

Regards,
ORF
PS: this meme summarizes this post
https://media.makeameme.org/created/uncertainty-uncertainty-everywhere.jpg
 
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