Thursday, September 28, 2017, 16:00
WHGA Auditorium
Friedrich-Karl Thielemann, Basel University and GSI Darmstadt
Abstract:
The rapid neutron-capture process (r-process) is responsible for making
about half of all heavy elements beyond Fe and is the only source of
elements beyond Pb and Bi. Despite all remaining uncertainties in
nuclear properties far from stability, the r-process is reasonably well
understood in terms of its nuclear reaction flow and necessary
environment conditions (neutron densities and temperatures).
However, the astrophysical site where it occurs is still highly
uncertain. We review the required nuclear physics input and address the
sites which have been suggested so far (among others): supernovae from
the core collapse of massive stars (CCSNe), compact binary (neutron
star) mergers, and magneto-rotational (MHD-jet) supernovae/magnetars.
The early "chemical" evolution of galaxies as well as recent additions
of radioactive species to the solar system require to attribute the
origin of the heavy r-process elements to very rare events. These must
occur with a frequency being smaller by about a factor of 1/100 compared
to regular CCSNe, thus excluding the latter as a major source. While
neutron star mergers are a clear source of heavy r-process elements
(plus gravitational waves and "electromagnetic" counterparts),
observations of low-metallicity stars indicate the existence of an
additional r-process source related to massive (and therefore fast
evolving) stars. Magneto-rotational supernovae, resulting in neutron
stars with extremely strong magnetic fields (magnetars), are the most
probable candidates for this site.