Vibrational instability of Population III very massive main-sequence stars due to the $\varepsilon$-mechanism

TL;DR

This study investigates the vibrational stability of Population III very massive stars, revealing that only the radial fundamental mode becomes unstable due to the b5-mechanism during early core hydrogen burning, potentially affecting their evolution.

Contribution

It is the first linear nonadiabatic analysis of vibrational stability in Population III very massive stars, identifying the specific mode and mechanism of instability.

Findings

Radial fundamental mode becomes unstable due to b5-mechanism.

Instability occurs after CNO cycle activation during early hydrogen burning.

Estimated mass loss due to instability suggests potential evolutionary impact.

Abstract

Very massive stars are thought to be formed in the early Universe because of a lack of cooling process by heavy elements, and might have been responsible for the later evolution of the Universe. We had an interest in vibrational stability of their evolution and carried out the linear nonadiabatic analysis of radial and nonradial oscillations for population III very massive main-sequence stars with $500-3000M_{\sun}$. We found that only the radial fundamental mode becomes unstable due to the $\varepsilon$-mechanism for these stars. The instability appears just after the CNO cycle is activated and the nuclear energy generation rate becomes large enough to stop the pre--main-sequence contraction, and continues during the early stage of the core hydrogen burning. Besides, we roughly estimated amount of mass loss due to the instability to know its significance.