Abstract:

In this talk, I will revisit the long-standing question in
stellar astrophysics: Why do post–main-sequence stars evolve into red
giants (RGs) or red supergiants (RSGs)? By comparing stellar evolution
models that reach the RG/RSG phase with those that remain blue, we
show that envelope expansion follows a refined “mirror principle.”
Building on this result, we construct steady-state envelope models to
identify the physically realizable configurations of stellar
envelopes. These solutions verify the refined mirror principle and
clarify the physical nature of the RG/RSG phase as a limiting
configuration of stellar structure, which is consistent with the
classical Hayashi limit.