Blue supergiants as descendants of magnetic main sequence stars

TL;DR

This study explores how magnetic fields in massive stars can influence their evolution, potentially leading to the formation of blue supergiants and altering their end-of-life outcomes.

Contribution

It introduces a new stellar evolution model incorporating magnetic suppression of convection, explaining the observed properties of blue supergiants and their evolutionary paths.

Findings

Magnetic fields can suppress convective core growth in massive stars.

Magnetic models produce blue supergiants during core helium burning.

Magnetic effects lead to lower luminosity in red supergiant phase.

Abstract

About 10$\%$ of the massive main sequence stars have recently been found to host a strong, large scale magnetic field. Both, the origin and the evolutionary consequences of these fields are largely unknown. We argue that these fields may be sufficiently strong in the deep interior of the stars to suppress convection near the outer edge of their convective core. We performed parametrised stellar evolution calculations and assumed a reduced size of the convective core for stars in the mass range 16 M$_{\odot}$ to 28 M$_{\odot}$ from the zero age main sequence until core carbon depletion. We find that such models avoid the coolest part of the main sequence band, which is usually filled by evolutionary models that include convective core overshooting. Furthermore, our `magnetic' models populate the blue supergiant region during core helium burning, i.e., the post-main sequence gap left by ordinary single star models, and some of them end their life in a position near that of the progenitor of Supernova 1987A in the HR diagram. Further effects include a strongly reduced luminosity during the red supergiant stage, and downward shift of the limiting initial mass for white dwarf and neutron star formation.