The recent detection of 60Fe in the cosmic rays provides conclusive evidence
that there is a recently synthesized component (few MY) in the GCRs (Binns et
al. 2016). In addition, these nuclei must have been synthesized and accelerated
in supernovae near the solar system, probably in the Sco-Cen OB association
subgroups, which are about 100 pc distant from the Sun. Recent theoretical work
on the production of r-process nuclei appears to indicate that it is difficult
for SNe to produce the solar system abundances relative to iron of r-process
elements with high atomic number (Z), including the actinides (Th, U, Np, Pu,
and Cm). Instead, it is believed by many that the heaviest r-process nuclei, or
perhaps even all r-process nuclei, are produced in binary neutron star mergers.
Since we now know that there is at least a component of the GCRs that has been
recently synthesized and accelerated, models of r-process production by SNe and
BNSM can be tested by measuring the relative abundances of these ultra-heavy
r-process nuclei, and especially the actinides, since they are radioactive and
provide clocks that give the time interval from nucleosynthesis to detection at
Earth. Since BNSM are believed to be much less frequent in our galaxy than SNe
(roughly 1000 times less frequent, the ratios of the actinides, each with their
own half-life, will enable a clear determination of whether the heaviest
r-process nuclei are synthesized in SNe or in BNSM. In addition, the r-process
nuclei for the charge range from 34 to 82 can be used to constrain models of
r-process production in BNSM and SNe. Thus, GCRs become a multi-messenger
component in the study of BNSM and SNe.Comment: Astro2020 Science White Pape