Aims. Following the renewed interest in axions as a dark matter component, we revisit the effects of energy loss by axion emission on the evolution of the first generation of stars. These stars with zero metallicity are assumed to be massive, more compact, and hotter than subsequent generations. It is hence important to extend previous studies, which were restricted to solar metallicity stars. Methods. Our analysis first compares the evolution of solar metallicity 8, 10, and 12 M stars to previous work. We then calculate the evolution of 8 zero-metallicity stars with and without axion losses and with masses ranging from 20 to 150 M. Results. For the solar metallicity models, we confirm the disappearance of the blue-loop phase for a value of the axion-photon coupling of gaγ = 10-10 GeV-1. We show that for gaγ = 10-10 GeV-1, the evolution of Population III stars is not much affected by axion losses, except within the range of masses 80-130 M. Such stars show significant differences in both their tracks within the Tc-ρc diagram and their central composition (in particular 20Ne and 24Mg). We discuss the origin of these modifications from the stellar physics point of view, and also their potential observational signatures.
Bibliographical noteFunding Information:
Acknowledgements. We would like to thank Jordi Isern for useful discussions during the early stage of this project. The work of K.A.O. was supported in part by DOE grant DE-SC0011842 at the University of Minnesota. The work of E.V. has been carried out at the ILP LABEX (under the reference ANR-10-LABX-63) supported by French state funds managed by the ANR within the Investissements d’Avenir programme under reference ANR-11-IDEX-0004-02.
© ESO, 2017.
- Elementary particles
- Stars: Population III
- Stars: evolution
- Stars: massive