Giant outbursts of clumpy material preceding Type II supernova 2024qiw

Observations of core-collapse supernovae (CCSNe) suggest that some massive stars undergo intense mass loss shortly before explosion, but the underlying mechanisms remain unknown. Here, we report evidence of giant outbursts of clumpy material from a massive star in the final decades before explosion. Photometric, spectroscopic, and polarimetric data of SN 2024qiw reveal a bumpy light curve, a broad Hα profile, and variable polarization, all consistent with interactions taking place between SN ejecta and clumpy circumstellar material, implying a mass-loss rate of ≳10⁻² M_⊙ yr⁻¹. Taken together, the most likely explanation is multiple major eruptions, similar to those of luminous blue variables (LBVs), but occurring shortly before explosion. This challenges standard stellar evolution theory by requiring either that LBVs explode terminally or that other evolutionary phases produce eruptive episodes. In spite of very high pre-SN mass loss, the resulting SN is classed as Type II, rather than Type IIn, highlighting diverse and previously unrecognized late-stage mass-loss processes.