In August 2025, astronomers found a supernova whose light reaches Earth as five separate images. It is called SN 2025wny, or SN Winny, and it sits more than 10 billion light-years away.
The discovery came after a six-year search by a group spanning the Technical University of Munich (TUM), Ludwig Maximilians University and the Max Planck Institutes. They had compiled a list of promising gravitational lenses and waited for an explosion to line up behind one. Sherry Suyu, associate professor of observational cosmology at TUM, put the chance of that alignment at lower than one in a million.
Two galaxies, five copies
Winny is a superluminous supernova, far brighter than typical stellar explosions. On its way to Earth, its light passed two foreground galaxies. Their gravity bent it into five paths of different lengths, and the result is five bluish copies of the same blast.
Most lensed supernovae seen before were magnified by galaxy clusters. “Until now, most lensed supernovae were magnified by massive galaxy clusters, whose mass distributions are complex and hard to model,” said Allan Schweinfurth, a TUM researcher. Two galaxies with smooth mass are easier. Schweinfurth and Leon Ecker built the first mass models of the lens and found the galaxies have not yet collided, which keeps the light paths regular.
The Large Binocular Telescope on Mount Graham in Arizona took the first high-resolution colour images. Its two 8.4-meter mirrors and adaptive optics cut through atmospheric blur to show the warm-toned lens galaxies and the five blue copies. Stefan Taubenberger is lead author of the identification study in Astronomy & Astrophysics.
What the delays could settle
Two methods for measuring the Hubble constant, the universe’s expansion rate, give different answers. One uses the local distance ladder, where each step relies on the one before and errors add up. The other uses the cosmic microwave background and depends on models of how the universe evolved. That split is the Hubble tension.
Because the images take routes of different lengths, they brighten at slightly different times. For Winny the expected delays are days to weeks. Combined with the lens mass, those gaps give the Hubble constant in a single step, with no ladder.
The catch is accuracy. Small stars in the lens can add microlensing that changes brightness, and the delays only translate into a number if the mass models hold up. Suyu has noted that only a handful of such lensed measurements have ever been attempted.
Follow-up observations from ground and space are under way to sharpen the delays as the supernova fades. If Winny’s result lines up with local measurements rather than early-universe data, it could mean dark energy evolves over time, or that new physics is needed.
Sources
- Five images of a supernova may reveal how fast the universe is expanding
- How Lensing Creates Multiple Supernova Images: SN Winny
