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Title: What drives heavy mass loss in the final years before collapse?
Plain: Many supernovae explode into thick gas that the star shed only years to decades before dying, far more than normal stellar winds can explain.
Precise: Early spectra with narrow, short-lived emission lines (flash ionization) show dense circumstellar material within $\sim 1\mathrm{e}15\,\mathrm{cm}$ in a large fraction of Type II supernovae, implying mass-loss rates ~1e-4 to 1e-2 M_sun/yr in the last years, far above steady red supergiant winds of ~1e-6 M_sun/yr. Identify the mechanism (wave energy transport from core convection in the last burning stages, binary interaction, pulsation-driven winds) and whether it also produces observed pre-explosion outbursts. Answer: a mechanism predicting circumstellar mass and extent versus progenitor mass and evolutionary stage.
Settled by: Pre-explosion monitoring of many nearby supernova progenitors combined with early spectra, compared with predicted outburst timing and circumstellar masses.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: 2023: SN 2023ixf in M101, the nearest Type II supernova in a decade, showed dense, confined circumstellar material.
Posed since: (empty)