Effects of axions on Population III stars

¹ Geneva Observatory, University of Geneva, Maillettes 51, 1290 Sauverny, Switzerland
arthur.choplin@unige.ch
² Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), CNRS/IN2P3, Univ. Paris-Sud, Université Paris-Saclay, Bâtiment 104, 91405 Orsay Campus, France
³ William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
⁴ Institut d’Astrophysique de Paris, UMR-7095 du CNRS, Université Pierre et Marie Curie; Sorbonne Universités, Institut Lagrange de Paris, 98bis bd Arago, 75014 Paris, France

Received: 25 April 2017
Accepted: 3 July 2017

Abstract

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 g_aγ = 10^-10 GeV^-1. We show that for g_aγ = 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 T_c–ρ_c 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.