Heavy elements from neutron star collisions?

  • #1
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Main Question or Discussion Point

I have seen it claimed online that the recently announced observation of a neutron-star merger by LIGO provides strong support for the hypothesis that heavy elements - gold and platinum were mentioned in particular - are mostly created in neutron-star collisions rather than in supernovas. Is this correct? Where can I find reliable information about this story?

In fact, where can I read about this hypothesis at all? Until today supernovas were the only source I heard mentioned for elements not created in the normal stellar fusion reactions.
 

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  • #2
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In fact, where can I read about this hypothesis at all? Until today supernovas were the only source I heard mentioned for elements not created in the normal stellar fusion reactions.
I have no source, but I heard about that mechanism many years ago. Thus it is not really new.
 
  • #3
phyzguy
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Wikipedia is always a good place to start. I think until about 2000 or so, it was thought that supernovae were the main source of all heavy elements. However, there were problems with getting enough of the "r-process" elements, which are neutron rich elements heavier than iron. The hypothesis that most of these elements come from decompressed neutron star material flung into interstellar space during neutron star mergers has been gaining favor. This recent Nature paper claims support for that hypothesis.
 
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A key piece of evidence for this scenario emerged recently with the discovery of extremely high levels of r-process elements in the Reticulum II dwarf galaxy, which orbits the Milky Way. "This implies that a single rare event produced the r-process material in Reticulum II. The r-process yield and event rate are incompatible with ordinary core-collapse supernovae, but consistent with other possible sites, such as neutron star mergers." Link: ArXiv
 
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  • #5
stefan r
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This article claims around 1% of the combined mass was ejected as heavy elements. Anyone know how they got that number. Does it eject iron too? Why not?

How much can rotation in the original neutron stars change the mass ejected?
 
  • #6
PAllen
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This article claims around 1% of the combined mass was ejected as heavy elements. Anyone know how they got that number. Does it eject iron too? Why not?

How much can rotation in the original neutron stars change the mass ejected?
I would think that what is emitted is initially Neutron star matter, which is mostly dense neutrons. This decays into heavy neutron rich isotopes. Within the neutron star, there are no atomic nuclei except perhaps in an outer skin.
 
  • #7
phyzguy
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As PAllen said, what is ejected is dense neutron star matter, which rapidly decays into a whole host of heavy elements. below is Figure 4 from this Arxiv paper, which shows the distribution of elements that result. One of the reasons people favor this model is that it seems to reproduce the observed abundances of heavy elements in the Solar System.

NS_Elements.png
 
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