  Nucleosynthesis of heavy nuclei in metal-poor stars is generally thought to
occur via the r-process because the r-process is a primary process that would
have operated early in the Galaxy's history. This idea is strongly supported by
the fact that the abundance pattern in many metal-poor stars matches well the
inferred Solar r-process abundance pattern in the mass range between the second
and third r-process abundance peaks. Nevertheless, a significant number of
metal-poor stars do not share this standard r-process template. In this Letter
we suggest that the nuclides observed in many of these stars are produced by
the r-process, but that it is prevented from running to completion in more
massive stars by collapse to black holes before the r-process is completed,
creating a "truncated r-process," or "tr-process." We find that the observed
fraction of tr-process stars is qualitatively what one would expect from the
initial mass function, and that an apparent sharp truncation observed at around
mass 160 could result from a combination of collapses to black holes and the
difficulty of observing the higher mass rare earths. We test the tr-process
hypothesis with r-process calculations that are terminated before all r-process
trajectories have been ejected. We find qualitative agreement between
observation and theory when black hole collapse and observational realities are
taken into account.
