Pulsations of red supergiant pair-instability supernova progenitors leading to extreme mass loss

TL;DR

This paper explores how pulsations in very massive, metal-free red supergiant stars can cause extreme mass loss before they explode as pair-instability supernovae, affecting their brightness, detectability, and circumstellar environment.

Contribution

It introduces a model for pulsationally induced mass loss in pair-instability supernova progenitors, highlighting its role in creating dense circumstellar media and influencing supernova observables.

Findings

Pulsations can induce mass-loss rates of 1e-4 to 1e-2 Msun/yr.

Dense circumstellar media may form around these stars before explosion.

Mass loss ceases when the star becomes more compact and stops pulsating.

Abstract

Recent stellar evolution models show consistently that very massive metal-free stars evolve into red supergiants shortly before they explode. We argue that the envelopes of these stars, which will form pair-instability supernovae, become pulsationally unstable and that this will lead to extreme mass-loss rates despite the tiny metal content of the envelopes. We investigate the pulsational properties of such models and derive pulsationally induced mass-loss rates, which take the damping effects of the mass loss on the pulsations selfconsistently into account. We find that the pulsations may induce mass-loss rates of ~ 1e-4 - 1e-2 Msun/yr shortly before the explosions, which may create a dense circumstellar medium. Our results show that very massive stars with dense circumstellar media may stem from a wider initial mass range than pulsational-pair instability supernovae. The extreme mass loss will cease when so much of the hydrogen-rich envelope is lost that the star becomes more compact and stops pulsating. The helium core of these stars therefore remains unaffected, and their fate as pair-instability supernovae remains unaltered. The existence of dense circumstellar media around metal-free pair-instability supernovae can make them brighter and bluer, and they may be easier to detect at high redshifts than previously expected. We argue that the mass-loss enhancement in pair-instability supernova progenitors can naturally explain some observational properties of superluminous supernovae: the energetic explosions of stars within hydrogen-rich dense circumstellar media with little 56Ni production and the lack of a hydrogen-rich envelope in pair-instability supernova candidates with large 56Ni production.