Astronomers hunted for nearly six years before the Zwicky Transient Facility in California caught the flash in late August 2025. A distant star had died in one blast, and its light was showing up in five places at once.
The object is SN 2025wny, nicknamed SN Winny. It is a superluminous supernova about 10 billion light-years away, far brighter than an ordinary stellar explosion. Two galaxies sit between it and Earth, and their gravity bends the light along five paths of different lengths. Most lensed systems throw up two or four images. Five is uncommon.
“The chance of finding a superluminous supernova perfectly aligned with a suitable gravitational lens is lower than one in a million,” said Dr. Sherry Suyu of the Technical University of Munich (TUM).
How the images were pinned down
Other telescopes joined in quickly. The Nordic Optical Telescope took early spectra, the Liverpool Telescope supplied extra images, and Keck Observatory added the next night’s data that completed the five-point picture. The Large Binocular Telescope on Mount Graham in Arizona then produced the first high-resolution colour image, using adaptive optics, which corrects for blur from Earth’s atmosphere, to separate the lens galaxies from the supernova copies.
Teams from TUM and Ludwig Maximilians University modelled the lens. Most earlier lensed supernovae were magnified by massive galaxy clusters with messy mass layouts. Winny is lensed by just two galaxies. Allan Schweinfurth pointed out that their light and mass profiles are smooth, which suggests they have not collided. Suyu said that geometry could allow a high-precision measurement of the Hubble constant.
A third way to measure expansion
The Hubble constant gives the universe’s expansion rate in kilometers per second per megaparsec. Two main methods disagree by several percent. One builds a distance ladder out of nearby objects, and small errors pile up at each rung. The other reads the cosmic microwave background and depends on assumptions about how the universe unfolded. The mismatch is called the Hubble tension.
Lensing offers a check that avoids both. Light on the longer paths arrives later, so the gaps between the five images depend on the lens mass and the expansion rate. For Winny those gaps are expected to run from days to weeks. Astronomers are tracking how each image brightens and fades to get them.
Microlensing from individual stars can nudge the brightness and muddy the timing. The lens galaxies’ mass also has to be modelled well, since the delays depend on it.
An earlier lensed supernova, Refsdal, found in 2014 and seen again in 2015, gave a value of about 66.6 km/s/Mpc in research published in Science in May 2026. Kelly, another researcher, stressed that several systems are needed before the disagreement can be settled.
The team’s identification study appeared in the journal Astronomy & Astrophysics. The timing measurements, and with them the Hubble constant, are still to come.
Sources
- Astronomers Stunned by One-in-a-Million Cosmic Event
- Five images of a supernova may reveal how fast the universe is expanding
- Astronomers spent six years chasing a cosmic miracle until they found a supernova so rare it appeared five times at once in the same sky
