Numerical experiments to help understand cause and effect in massive star evolution

The evolution of massive stars is affected by a variety of physical processes, including convection, rotation, mass-loss, and binary interaction. Because these processes modify the internal chemical abundance profiles in multiple ways simultaneously, it can be challenging to determine which properties of the stellar interior are primarily driving the overall evolution. Building on previous work, we develop a new modelling approach called snapshot that allows us to isolate the key features of the internal abundance profile that drive the evolution of massive stars. Using our approach, we compute numerical stellar structure models in thermal equilibrium covering key phases of stellar evolution. For the main sequence, we demonstrate that models with the same mass and very similar surface properties can have different internal distributions of hydrogen and convective core masses. We discuss why massive stars expand after the main sequence and the fundamental reasons for why they become red, blue or yellow supergiants. For the post-main sequence, we demonstrate that small changes in the abundance profile can cause very large effects on the surface properties. We also discuss the effects that produce blue supergiants and the cause of blue loops. Our models show that massive stars with lower metallicity tend to be more compact due to the combined effect of lower CNO abundances in the burning regions and lower opacity in the envelope.

Automated summary

The evolution of massive stars is influenced by various physical processes, and the abundance distribution plays a crucial role. A new modelling approach called snapshot is developed to identify the key features of the abundance profile. It is found that massive stars with the same mass and similar surface properties can have different internal distributions of hydrogen and convective core masses. Small changes in the abundance profile can have significant effects on the surface properties. Lower metallicity leads to more compact massive stars.