The r-Process in Metal Poor Stars and Black Hole Formation

TL;DR

This paper proposes the 'truncated r-process' hypothesis, suggesting that black hole formation in massive stars halts heavy element synthesis, explaining observed variations in metal-poor stars' abundance patterns.

Contribution

It introduces the concept of a truncated r-process caused by black hole collapse, providing a new explanation for the diversity in metal-poor stars' nucleosynthesis signatures.

Findings

Qualitative agreement between observations and truncated r-process models.

The observed fraction of tr-process stars aligns with initial mass function predictions.

Sharp truncation at mass 160 may result from black hole formation and observational biases.

Abstract

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.