The s-process in the Galactic halo: the fifth signature of spinstars in
  the early Universe?
  Very old halo stars were previously found to show at least four different
abundance 'anomalies', which models of fast rotating massive stars (spinstars)
can successfully account for: rise of N/O and C/O, low 12C/13C and a
primary-like evolution of Be and B. Here we show the impact of these same stars
in the enrichment of Sr and Ba in the early Universe. We study if the s-process
production of fast rotating massive stars can offer an explanation for the
observed spread in [Sr/Ba] ratio in halo stars with metallicity [Fe/H]< -2.5.
By means of a chemical inhomogeneous model we compute the enrichment of Sr and
Ba by massive stars in the Galactic halo. Our model takes into account, for the
first time, the contribution of spinstars. Our model (combining an r-process
contribution with a s-process from fast rotating massive stars) is able to
reproduce for the first time the observed scatter in the [Sr/Ba] ratio at
[Fe/H]< -2.5. Toward higher metallicities, the stochasticity of the star
formation fades away due to the increasing number of exploding and enriching
stars, and as a consequence the predicted scatter decreases. Our scenario is
again based on the existence of spinstars in the early Universe. Very old halo
stars were previously found to show at least four other abundance 'anomalies',
which rotating models of massive stars can successfully account for. Our
results provide a 5th independent signature of the existence of fast rotating
massive stars: an early enrichment of the Universe in s-process elements.
