What is considered the leading source for the creation of the very heaviest elements via the rapid neutron capture process?

Answer

Binary neutron star mergers

Binary neutron star mergers generate an environment of unparalleled density and neutron flux during the resulting kilonova, and this is now considered the leading source for $r$-process element creation.

What is considered the leading source for the creation of the very heaviest elements via the rapid neutron capture process?
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