&Bullet; physics 14, p66
New analysis of nuclear reaction data finds holes in a theory about the first stars.
Stars are dutiful recyclers. The material used and discarded by one generation of stars is taken up and reused by the next. However, this cycle process struggles to explain the surprisingly high levels of calcium in stars that formed early. Astrophysicists have suggested that these ancient stars were seeded by a first generation that ended up in “weak supernovae” producing calcium, but few other heavy elements. However, a new analysis of the nuclear reaction measurements suggests that this model may not be as solid  .
The first massive stars formed shortly after the Big Bang and burned brightly but briefly. Astronomers can infer information about this generation by looking at existing stars that were born from their remains. These ancient stars lack heavy elements, suggesting that the earliest stars ended up whimpering rather than bangs. In order for this faint supernova model to explain the calcium data, the first stars must have burned hydrogen to calcium through a series of so-called breakout reactions.
James deBoer of the University of Notre Dame in Indiana and his colleagues compiled 70 years of data on a particular breakout reaction, in which a fluorine nucleus traps a proton and creates a neon nucleus and a gamma ray. They performed a reaction network analysis that took competing reactions into account. For example, a fluorine nucleus can capture a proton but produce an oxygen nucleus and an alpha particle – a step back on the path to calcium. The analysis showed a much greater uncertainty in the fluorine burst reaction rate than previously reported, raising doubts about the fainting supernova model. The authors say that lower energy measurements are required to reduce the uncertainty in reaction rates.
Michael Schirber is the corresponding editor for physics based in Lyon, France.
- R. deBoer et al., “
Reaction rates and their effect on calcium production in Population III stars due to hot CNO eruptions ” Phys. Rev. C.103055815 (2021).