The first stars in the Universe formed about 400 million years after the Big Bang. Inside of these stellar furnaces, nuclear processes fused the hydrogen and helium made by the primordial nucleosynthesis into heavier elements. Each of these stars left ashes with a unique abundance pattern signature after their death. It is vital to our understanding of the properties of the first stars and the formation of the first galaxies to verify the predicted composition of stellar ashes by comparing to observational data. Hence proper modeling of the stars and their nuclear reactions is required. One reaction having a potentially large influence on key properties of the abundance pattern is the fusion of two 12C nuclei into 23Mg and one neutron. The measurement of stellar reaction rates in the laboratory is difficult because the processes typically have very low probabilities making a successful reaction quite rare.
Recently, an international nuclear astrophysical team led by Dr. Xiaodong Tang (IMP, CAS) and Dr. Bucher (LLNL, US) has successfully measured this carbon fusion reaction at stellar energies for the first time using a laboratory accelerator. With this new measurement, they have significantly improved the precision of this rate inside stars. Their new result is crucial to the identification of the signature of the Universe’s elusive first generation of stars and their supernovae.
This work was jointly supported by funding agencies such as National Science Foundation (US), Chinese Academy of Sciences, National Natural Science Foundation of China. Other institutions involved in the research include the University of Notre Dame (US), Lawrence Livermore National Laboratory (US), Monash University (Australia), Shanghai Jiao-Tong University (China), University of Minnesota (US), China Institute of Atomic Energy, Konkoly Observatory (Hungary), University of Basel (Switzerland) and University of California, Santa Cruz (US).
This work was published in Physical Review Letter (Phys. Rev. Lett. 114, 251102 (2015)).
The article can be linked as follows: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.251102
Fig. 1 First stars after their death left ashes with a unique abundance pattern. Verification of the existence of such a remnant is vital to our understanding of the properties of the first stars and the formation of the first galaxies. Proper modeling of the stars and their nuclear reactions is essential for providing a reliable prediction. The 12C(12C,n)23Mg reaction rate is important for the production of odd-Z elements, such as Na and Al. Image above is composed by IMP based on a picture from NASA.
Fig. 2 modified astrophysical S* factors for the 12C(12C,n)23Mg reaction; Lower figure: the corresponding Gamow yield calculated at a typical carbon shell burning temperature (1.1 billion degree). Before this work, experimental measurement (purple open circles) was limited at energies above the astrophysical energies (2.6 MeV<Ecm<3.7 MeV) with large uncertainty. The deviation of the old theoretical prediction (red line) from the experimental result is as large as 400%. In this work, the 12C(12C,n)23Mg reaction cross section has been measured for the first time within the important astrophysical energy range (black points). A new resonance at Ecm=3.4 MeV has been found. What’s more, a novel extrapolating method has been developed to significantly improve the systematic error below Ecm=3.1 MeV (blue points). The new result is crucial to the identification of the signature of the Universe’s elusive first generation of stars and their supernovae.(Image by IMP)