The universality of the rapid neutron-capture process revealed by a
  possible disrupted dwarf galaxy star
  The rapid neutron-capture process or r-process is thought to produce the
majority of the heavy elements (Z > 30) in extremely metal-poor stars. The same
process is also responsible for a significant fraction of the heavy elements in
the Sun. This universality of the r-process is one of its characteristic
features as well as one of the most important clues to its astrophysical
origin. We report the discovery of an extremely metal-poor field giant with
[Sr,Ba/H] $\approx$ -6.0 and [Sr, Ba/Fe] $\approx$ -3.0, the lowest abundances
of strontium and barium relative to iron ever observed. Despite its low
abundances, the star 2MASS J151113.24-213003.0 has [Sr/Ba] = -0.11 +/- 0.14 and
therefore its neutron-capture abundances are consistent with the main solar
r-process pattern that has [Sr/Ba] = -0.25. It has been suggested that
extremely low neutron-capture abundances are a characteristic of dwarf
galaxies, and we find that this star is on a highly-eccentric orbit with
apocenter $\gtrsim$100 kpc that lies in the disk of satellites in the halo of
the Milky Way. We show that other extremely metal-poor stars with low [Sr,Ba/H]
and [Sr,Ba/Fe] plus solar [Sr/Ba] tend to have orbits with large apocenters,
consistent with a dwarf galaxy origin for this class of object. The
nucleosynthesis event that produced the neutron-capture elements in 2MASS
J151113.24-213003.0 must produce both strontium and barium together in the
solar ratio. We exclude contributions from the s-process in intermediate-mass
AGB or fast-rotating massive metal-poor stars, pair-instability supernovae, the
weak r-process, and neutron-star mergers. We argue that the event was a Pop III
or extreme Pop II core-collapse supernova explosion.
