Why stars inflate to and deflate from red giant dimensions, II: replies to critics

TL;DR

This paper defends the authors' previous explanation of stellar evolution phenomena, reaffirming the importance of opacity-driven thermal instabilities in star inflation and contraction, and addresses criticisms that questioned their earlier work.

Contribution

It clarifies and reaffirms the role of thermal instabilities in stellar evolution, countering criticisms and emphasizing their significance in star size changes.

Findings

Thermal instabilities are central to star inflation and deflation.

Criticisms of previous models are shown to be insubstantial.

The importance of opacity-driven processes in stellar evolution is reaffirmed.

Abstract

In a 1992 paper of ours the role of opacity-driven thermal instabilities in shaping the course of stellar evolution was amply illustrated. This included the classical issue of ``{\it why stars become red giants"} as well as the subsequent formation of extended ``Cepheids" {\it blue loops} during the helium burning phases. Our explanation of these evolutionary phenomena has been occasionally dismissed with just a few words in refereed or not refereed publications. In a most recent case, the fact that, through the years, I did not reply to these criticisms is interpreted as evidence that they were well founded. In this paper it is made clear that this is not at all the case, the leading role of such instabilities is instead reaffirmed and the criticisms are shown to be insubstantial.