Astronomers discover the first gravitationally lensed superluminous supernova

An international team of astronomers led by Oskar Klein Centre (OKC) researcher Joel Johansson has discovered SN 2025wny, the first spatially resolved, gravitationally lensed superluminous supernova ever observed. The discovery provides a striking confirmation of Einstein’s theory of General Relativity and a rare window into a powerful stellar explosion from the early Universe.

A cosmic magnifying glass reveals a record-distant explosion

The supernova SN 2025wny lies at an extraordinary distance – its light has travelled around 10 billion years to reach us. At the time the light was emitted, the Universe was only about 4 billion years old.

A supernova this distant would normally be far too faint to discover from earth. However, thanks to two foreground galaxies, acting as a gravitational lens, the supernova appears about 50 times brighter, making it visible to ground-based telescopes.

“This is nature’s own telescope,” says Joel Johansson, lead author and researcher at the Oskar Klein Centre, Stockholm University. “The magnification lets us study a supernova at a distance where detailed observations would otherwise be impossible.”

A new method to probe the expansion of the Universe

The gravitational lensing effect does more than magnifying the supernova – it produces several distinct, spatially separated images of the same explosion. Each lensed image of the supernova takes a slightly different path around the deflecting galaxies, reaching Earth at different times. These time differences offer an independent, highly promising method to measure the Hubble constant, which describes how fast the Universe is expanding. 

A current hot topic in modern cosmology is the so called “Hubble tension”, which refers to the growing discrepancy between two precise and independent measurements of how fast the Universe is expanding; one based on observations of the early cosmos and the other on nearby objects. This may suggest that our current cosmological model is incomplete, or that one of the methods currently used is flawed.

Ariel Goobar, group leader at the OKC and part of Joel Johansson’s research team considers this new approach to be a technical breakthrough: 
“A lensed supernova with multiple, well-resolved images, provides one of the cleanest ways to measure the expansion rate of the Universe. SN 2025wny is an important step toward resolving one of cosmology’s most significant challenges,” Ariel Goobar says.

A surprising and exceptionally hot explosion

Superluminous supernovae are a relatively newly discovered class of cosmic explosions, which are extremely energetic and rare in nature. Because the Universe is expanding, ultraviolet light emitted by SN 2025wny is “redshifted” to optical wavelengths, and can be detected with telescopes on the ground. The team’s observations show that SN 2025wny is unusually hot and bright, even for a superluminous supernova in its early stages.

The supernova is so bright that it lit up its host galaxy, allowing researchers to study its composition from narrow absorption lines in the spectrum. It appears to be a low-density, low-metallicity, star-forming dwarf galaxy, consistent with the kind of environments thought to produce superluminous supernovae. Seeing such a system at this early cosmic epoch provides rare insight into how stars and galaxies evolved in the young Universe.

How the Discovery Was Made

The discovery relied on a chain of cutting-edge observatories working together:
Zwicky Transient Facility (ZTF) – a wide-field survey telescope at Palomar Observatory in California – first detected the explosion during its nightly monitoring of the sky.
While scanning through the daily list of new transients found by ZTF, Joel Johansson noticed that one of them was particularly promising. The Dark Energy Spectroscopic Instrument (DESI) had already provided the distance of the nearest galaxy to SN 2025wny, and archival images suggested that the surrounding galaxies could be lensed background galaxies. This immediately signalled that any associated transient must be either exceptionally bright and/or strongly lensed.

Early spectroscopy with the Nordic Optical Telescope (NOT) on La Palma in the Canary Islands showed that the transient was indeed a supernova, but the spectrum was difficult to match with more common supernova types the team had seen before.
On the same mountain, the Liverpool Telescope (LT) – somewhat larger than ZTF and with sharper imaging – delivered the crucial breakthrough: the team was able to resolve four separate images of SN 2025wny.

Jacob Wise, a PhD student at Liverpool John Moores University (LJMU) and lead of the LT programme, was the first to recognise the multiple-image nature of SN 2025wny: 
“I couldn’t believe my eyes when I saw the data, I thought that it must have been an artefact from the camera. However, when I carefully looked at our data from previous nights, I could still clearly see the multiple lensed images of the supernova. The realisation of what we had just discovered was by far the most exciting moment of my career so far,” he says.

His PhD advisor, Professor Dan Perley (LJMU), confirmed the detection and says: 
“The instant Jacob sent me the images I knew we had found something big - no one had ever seen multiple images of a supernova with a ground-based telescope before, and there it was in front of us, clear as day.”

Finally, the Keck Observatory (10-m telescopes) on Hawaii provided decisive spectra, confirming both the supernova type and its extreme distance. Yu-Jing Qin, a postdoctoral researcher at Caltech, led a series of spectroscopic observations targeting each of the individual supernova images and the lensing galaxies. 
The Keck spectra revealed a forest of narrow absorption lines from the supernova’s host galaxy – the fingerprints of elements such as carbon, iron and silicon – which nailed down the redshift and nature of the event.

What Comes Next?

SN 2025wny demonstrates that strongly lensed supernovae at very high redshifts can be found and resolved with existing ground-based surveys.

The cosmology community is eager to measure the expansion rate of the Universe, and SN 2025wny provides an essential proof of concept for future discoveries from the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST). Hundreds of lensed supernovae should be within reach in LSST, following the technique pioneered by the SN 2025wny discovery team. 

Follow-up observations with the Hubble and James Webb Space Telescopes are already underway. These data will refine the lens model, map the positions of the multiple images with exceptional precision, and ultimately measure the time delays needed for a new, independent determination of the Hubble constant.

The magnification also gives astronomers a chance to study the explosion mechanism of a distant superluminous supernova and its surrounding environment in unprecedented detail.

The Team

The work was led by researchers at:

• Oskar Klein Centre, Stockholm University: Joel Johansson, Ariel Goobar, Cameron Lemon, Edvard Mörtsell and Jacob Osman Hjortlund at the Physics department. Claes Fransson, Anjasha Gangopadhyay, Ragnhild Lunnan, Avinash Singh, Jesper Sollerman and Konstantinos Tsalapatas at the Astronomy department.
• Liverpool John Moores University: Dan Perley, Jacob Wise and Zoë McGrath
• with contributions from the global ZTF Collaboration

Learn more about how Supernova are identified:
Explaining supernova Zwicky with watercolours

The article

The article “Discovery of SN 2025wny: A Strongly Gravitationally Lensed Superluminous Supernova at z = 2.01” is published in The Astrophysical Journal Letters. DOI: 10.3847/2041-8213/ae1d61