Effects of axions on Population III stars

TL;DR

This study investigates how axion-induced energy loss influences the evolution of Population III stars, revealing notable effects on their internal structure and evolution, especially in stars with masses between 80 and 130 solar masses.

Contribution

It extends previous stellar evolution models by analyzing zero-metallicity stars and their interaction with axion energy loss, highlighting effects not seen in solar metallicity stars.

Findings

Axion losses affect the evolution of Population III stars in specific mass ranges.

Significant differences observed in internal composition and evolutionary tracks for 80-130 M$_\odot$ stars.

Confirmation of the disappearance of the blue loop phase at certain axion-photon couplings.

Abstract

Following the renewed interest for 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 supposed to be massive, more compact, and hotter than subsequent generations. It is hence important to extend previous studies restricted to solar metallicity stars. Our analysis first compares the evolution of solar metallicity 8, 10 and 12 M$_\odot$ 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$_\odot$. For the solar metallicity models, we confirm the disappearance of the blue loop phase for a value of the axion-photon coupling, $g_{a\gamma}=10^{-10} {\rm GeV}^{-1}$. Regarding the Pop. III stars, we show that for $g_{a\gamma}=10^{-10} {\rm GeV}^{-1}$, their evolution is not much affected by axion losses except within the range of masses 80$-$130 M$_\odot$. Such stars show significant differences both in their tracks within the $T_c$-$\rho_c$ diagram and in their central composition (in particular $^{20}$Ne and $^{24}$Mg). We discuss the origin of these modifications from the stellar physics point of view, and their potential observational signatures.