The r-process in Metal-poor Stars and Black Hole Formation

• Published in: Astrophysical journal. Letters Vol. 744; no. 1; pp. L14 - 4
• Main Authors: Boyd, R. N, Famiano, M. A, Meyer, B. S, Motizuki, Y, Kajino, T, Roederer, I. U
• Format: Journal Article
• Language: English
• Published: United States IOP Publishing 01.01.2012
• Subjects: Abundance; ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; Black holes (astronomy); Collapse; ELEMENT ABUNDANCE; GALAXIES; GRAVITATIONAL COLLAPSE; HEAVY NUCLEI; MASS; Massive stars; Mathematical analysis; Metallicity; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; R PROCESS; Rare earth metals; RARE EARTHS; Running; STARS
• ISSN: 2041-8205; 2041-8213
• DOI: 10.1088/2041-8205/744/1/L14

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-earth elements. 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.