So, I would imagine this question would have been asked here long ago but the suggested questions and Google is really letting me down now. So, as far as I can tell Plutonium is the heaviest naturally occurring element via electron-capture, but I have not found anything to suggest plutonium is formed in supernovae. So, my question is, Is Uranium really the heaviest element formed in a supernova? If so, is that a known fact or is it conjecture from observation? By that, I am asking if there are mathematical models and whatnot or some other method that it is known plutonium cannot form in supernovae. If it is known, then how is it known.

Also, is it possible that the few so-called "super-Chandraskhar" limit supernovae could possibly form heavier elements?

  • $\begingroup$ Here's a scientific American article (1998), that suggests the earth has plutonium created in a supernova. scientificamerican.com/article/do-transuranic-elements-s There's no logical reason I can think of, why a super-nova wouldn't create, at least in trace amounts, most of what we can create in a lab. $\endgroup$
    – userLTK
    Apr 30, 2015 at 6:11

1 Answer 1


Practically all the elements heavier than lead are created by neutron capture in the r-process. This requires the explosive conditions of a supernova or neutron star merger.

In terms of some limit, I'm not sure how to answer. Stuff that's heavier than Uranium has a short half life compared to the age of the Earth, so there's not much to be found. They may have been produced in supernovae, but rapidly decayed.

We do know (at least theoretically) that much heavier elements were created indirectly by a supernova, in that they exist in the crust of a neutron star. Calculations show that atomic masses of more than around 300 are possible at densities of a few $10^{16}$ kg/m$^3$, largely due to the suppression of beta decay by degenerate electrons.


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