Pulsations change the structures of massive stars before explosion: interpreting SN 2023ixf and SN 2024ggi

TL;DR

This study shows that pulsations in massive red supergiants significantly influence their pre-supernova properties and observable features, challenging the common assumption of hydrostatic equilibrium in supernova progenitor models.

Contribution

It introduces hydrodynamical models of pulsating RSGs, demonstrating their impact on supernova observations and questioning traditional static progenitor assumptions.

Findings

Pulsations cause large variations in pre-SN luminosity and temperature.

Pulsations can explain early-excess emission in SN light curves.

Models match observations of SN 2023ixf better than static models.

Abstract

Massive red supergiants (RSGs) are known to become hydrodynamically unstable before they explode. Still, the vast majority of supernova (SN) models assume RSG progenitors in hydrostatic equilibrium. Here, we follow the hydrodynamic evolution of RSGs with different masses and the development of radial envelope pulsations. Pulsations significantly alter the observable pre- and post-SN properties, and their importance increases substantially as a function of initial mass. We demonstrate that inferring core masses, let alone initial masses, from a single pre-SN luminosity and effective temperature of high-mass RSGs is inadvisable, as these can vary by an order of magnitude during the pulsation. We find that pulsations can naturally lead to "early-excess" emission in SN light curves and to variations in early photospheric velocities, which can help break degeneracies in type-II SNe. We compare to SN 2023ixf and SN 2024ggi, for which pulsating RSG progenitors were reported. We demonstrate that the pre- and post-SN characteristics of SN 2023ixf agree very well with our exploding pulsating RSG model and exhibit meaningful differences from hydrostatic models. The data coverage is insufficient to break all degeneracies. We find insufficient evidence for the claimed pulsation period of the SN 2024ggi progenitor, as it matches Spitzer's orbital period. This study underscores the importance of hydrodynamical pre-SN stellar models, in particular for massive stars from $\gtrsim 15\,\rm{M}_{\odot}$. It implies an important shift in our understanding of the last stages of massive star evolution, the interpretation of pre-SN properties, the connection between SNe and their progenitors, and the missing RSG problem.