Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: amalia on 13/12/2019 14:25:29
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Scott got in touch with a question:
They say that heavier elements are created by high energy events (supernovae, merging neutron stars, etc.). Were any of these heavier elements created by the Big Bang?
Do you know the answer?
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Most of what I know about this, I learned here: https://en.wikipedia.org/wiki/Nucleosynthesis
Very interesting stuff indeed!
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Everything we see was created by the big bang, so in that sense yes.
There were no atomic nuclei right at the big bang. It wasn't until about 3-20 minutes later that atomic nuclei were first formed (and a third of a million years before atoms), little that was larger than lithium, but odds are a few isolated heavy elements were created around that time. Not sure if that counts as being created by the big bang more than the other ones.
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odds are a few isolated heavy elements were created around that time
In this context, "heavy" would mean Beryllium or Carbon.
I suspect that if protons and neutrons were equally common in the Big Bang, the BB would have produced a lot of heavy elements: iron and beyond.
- However, we don't see this, which leads me to think that the BB composition was mostly electrons and protons (nobody really knows what it was before energies dropped low enough for these to form...).
- Initially, energies were too high for electrons and protons to bond
- And two colliding protons is not stable
- So the rate-limiting step is two protons colliding and one of them turning into a neutron in the instant before they fly apart. This produces Deuterium.
- Deuterium combines very readily into Helium; Helium is extremely stable (measured as binding energy per nucleon). This leaves very little Deuterium, but a fair amount of Helium.
- Any larger nuclei are less stable than Helium (measured as binding energy per nucleon).
- Elements larger Calcium need an excess of neutrons to remain stable, which means they are subject to the same rate-limiting step as Deuterium, in addition to the rate-limiting step of growing above Helium.
See: https://en.wikipedia.org/wiki/Neutron%E2%80%93proton_ratio#/media/File:Isotopes_and_half-life.svg
The above discussion assumes that nuclei just "grow"., in a hot, dense environment But I suspect that there are also processes tearing large nuclei apart.
A Chemistry Analogy
In chemistry, if you heat up a complex molecule, it tend to shake itself apart
- The least stable bonds break first
- The more stable bonds break at higher temperatures
- If you go higher, it breaks into individual atoms
- And if you go to high enough temperatures, you don't have atoms, but a plasma (different building blocks)
Application to Nucleosynthesis
If you did heat up a mixture of light and heavier nuclei (< Oxygen), at extreme temperatures and pressures (such as occurred in the BB)...
- The larger and more unstable nuclei would tend to be smashed apart
- Leaving only the most stable ones - Protons and Helium
- The trace of Lithium remaining represents the dying gasp of nucleosynthesis as the BB fireball expanded and cooled
- It is thought that traces of Beryllium-7 would have been produced, but this is unstable, and decays by itself into smaller nuclei.
See: https://en.wikipedia.org/wiki/Nuclear_binding_energy#Nuclear_binding_energy_curve
The reactions occurring between light nuclei are easily studied in particle accelerators, and by measuring the charge/mass ratio of isotopes.
- These reactions are vital to the study of stellar fusion and fusion bombs, so they have been well studied.
- So when astrophysicists expect that Hydrogen, Deuterium, Helium and Lithium remained after the BB, you could assume it is quite well studied
- Of course, detecting primordial neutrinos, black holes and Dark Matter is an ongoing challenge...
https://en.wikipedia.org/wiki/Nucleosynthesis#Big_Bang_nucleosynthesis
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The simple answer amalia is No.
Only a few more complex nuclei were created during the big bang. Mostly helium, a smaller quantity of Duterium and a tiny quantity of lithium.
The reason for this is that there is an unstable gap in stable nuclei in that two helium nuclei cannot fuse to form a beryllium nucleus it needs another neutron to hold them together and to get beyond this impasse requires the high temperatures densities and pressures that are found in the cores of stars to normal stars make all the elements from beryllium to iron that are common on our planet. They cannot get beyond this because nuclear fusion energy runs out at this point. anf the formation of all the elements beyond iron are formed using violent stellar core collapses and supernovas.
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the formation of all the elements beyond iron are formed using violent stellar core collapses and supernovas.
It is true that elements slightly heavier than iron can be created during a supernova.
- This builds up from iron by adding protons (Hydrogen nuclei), an endothermic process
But the more modern idea is that most heavy elements (gold, uranium and above) are formed in neutron star collisions.
- This was confirmed by optical observation of a neutron star collision detected by LIGO
- This is caused by decay of the super-nucleus that is a neutron star, once (parts of) it is in free-fall, and the constraining compression of its enormous gravity is removed
See: https://en.wikipedia.org/wiki/Nucleosynthesis#Neutron_star_collision