Dance to Demise -- How Massive Stars May Form Dense Circumstellar Shells Before Explosion

TL;DR

This paper tackles how red supergiant (RSG) progenitors of core-collapse SNe can form dense circumstellar shells before explosion. Using MESA with pulsation-driven superwinds and post-shock dynamical ejections, the authors generate time-dependent mass-loss histories for $M_{init}=12$–$20\,M_\odot$ and construct accelerated wind CSM profiles with a $\beta$-law velocity field to compute $\rho(r)$ and the line-of-sight column density $N_H(r)$. They compare model CSM densities and $N_H$ to multi-wavelength observations of SNe 2023ixf, 2020ywx, 2017hcc, 2005ip, and 1998S, finding good agreement for plausible parameter choices (e.g., $\alpha\gtrsim 2$ and $M_{init}\gtrsim 15\,M_\odot$) and offering a physical mechanism for the observed flash-ionization, X-ray, and radio signatures. The results imply that single-star evolution with pulsation-driven mass loss and subsequent dynamical ejections can account for the diversity of SN environments and early-time CSM interactions, with important implications for dust formation and pre-explosion mass budgets. The work highlights the need to incorporate rotation, metallicity, and binarity in future models and points to computational innovations (GPU-accelerated networks, neural surrogates) to extend pre-SN yield predictions toward larger parameter spaces and higher fidelity dust estimates.

Abstract

We investigate the evolution of red supergiant (RSG) progenitors of core-collapse supernovae (SNe) with initial masses between $12$ and $20~\mathrm{M}_{\odot}$, focusing on effects of enhanced mass loss due to pulsation-driven instabilities in their envelopes and subsequent dynamical ejections during advanced stages of nuclear burning. Using time-dependent mass loss rates from detailed Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution models, including prescriptions for both pulsation-driven superwinds and shock-induced ejections, we construct the circumstellar medium (CSM) before the SN explosion. We calculate resulting CSM density profiles and column densities considering the radiation-driven acceleration of the stellar wind. Our models produce episodes of enhanced mass loss $\sim 10^{-4}-10^{-2}~ \mathrm{M}_{\odot}~\mathrm{yr}^{-1}$ in the last centuries-decades before explosion forming dense CSM ($\gtrsim10^{-15}~\mathrm{g~cm}^{-3}$ at distances $\lesssim10^{15}~\mathrm{cm}$) - consistent with multi-wavelength observations of Type II SNe such as SN 2023ixf, SN 2020ywx, SN 2017hcc, SN 2005ip and SN 1998S. The formation of such dense CS shells, as predicted by our single star RSG models, provides a natural explanation for observed flash-ionization signatures, X-ray and radio emission, and has important implications for dust formation around Type II SNe.

Figures (11)

• Figure 1: Growth rate of radial oscillations, $\eta$, as a function of stellar parameters (radius, mass, and Kelvin-Helmholtz time-scale of the envelope); the solid line represents a linear least-squares fit.
• Figure 2: (Top) Evolution of the stellar radius (black curve plotted on the left axis) in a set of hydrodynamic MESA model sequences with initial mass $M_\mathrm{init} = 15~\mathrm{M}_\odot$ in the RSG phase until shock breakout at the surface when Mach Number ($:= v_{surf}/c_{sound}$) exceeds unity (shown in red on the right axis). (Bottom) Corresponding evolution of a set of MESA models with varying initial masses between $12 - 18\ M_\odot$ in the HR diagram.
• Figure 3: Mass loss histories of two model sequences with $M_{\rm{init}}=16~\rm{M}_\odot$ for $\alpha=0.0$ (dashed blue line) which corresponds to the Dutch wind in MESA, scaled down by a factor of 0.2 (see Section \ref{['section: pulsating RSGs']}), and $\alpha=4.25$ (solid red line) which gives an enhanced "superwind" with $\dot M\sim10^{-3}$ M$_{\odot}$$\rm{yr}^{-1}$ over the last $\sim10^{3}~\rm{yrs}$.
• Figure 4: Mass-loss histories of two model sequences as described in Section \ref{['subsection : pdsw']} with $M_{\rm{init}}=16~\rm{M}_\odot$ for $\alpha=4.35$ (in dotted red) and including dynamical mass ejections (in solid red) which gives episodic enhancements in mass-loss with $\dot M\sim10^{-2}$ M$_{\odot}$$\rm{yr}^{-1}$ over the last $\sim30~\rm{yrs}$ prior to CC.
• Figure 5: Evolution of MESA model sequences with varying initial masses showing the mass-loss history due to PDSWs and dynamical ejections as described in Sections \ref{['subsection : pdsw']} and \ref{['subsection : deso']} respectively: top left panel shows the mass loss history of a sequence of MESA models with $M_{\rm{init}}=15$ M$_{\odot}$ prior to CC, showing enhanced mass-loss rates of $\dot M\gtrsim10^{-5}$ M$_{\odot}$$\rm{yr}^{-1}$ for $\alpha\ge2$, due to PDSWs. These models do not reach the regime of dynamical ejections; top right panel shows MESA models with $M_{\rm{init}}=16$ M$_{\odot}$ exhibiting episodic mass loss due to dynamical ejections for $\alpha\gtrsim4.35$ following a superwind phase, with average mass loss rates exceeding $10^{-2}$ M$_{\odot}$$\rm{yr}^{-1}$ within $100$ yrs of CC; bottom left panel shows MESA model sequences for $M_{\rm{init}}=17$ M$_{\odot}$ , showing similar episodes of elevated mass loss due to dynamical ejections occur at $\alpha\gtrsim3.6$ with earlier onset of such phases observed at higher values of $\alpha$; bottom right panel shows MESA models for $M_{\rm{init}}=18$ M$_{\odot}$ , showing onset of the dynamical ejections occuring at $\alpha\gtrsim2.8$ between $1-20$ yrs of CC.