SN 2025wny — "SN Winny" — is the first superluminous Type I supernova caught in the act of gravitational lensing: a massive foreground galaxy bends and amplifies its light, splitting it into five separate images. Such systems are rare and valuable, as the different arrival times of each image can be used to independently measure the Hubble constant.
All five images were resolved with the Keck telescope at a resolution of ~0.065 arcseconds. Using their precise positions as constraints, the team modelled the mass distribution of the lensing galaxy — two independent approaches agreed closely, placing its mass within the Einstein radius at roughly 4.44 × 10¹¹ solar masses, consistent with DESI spectroscopy.
One puzzle remains: image A is 2–3 times brighter than any smooth lens model can explain. The likely culprit is unseen mass along the line of sight — possibly clumps of dark matter too small and faint to detect directly.