Five-Time Supernova Discovery May Solve a Century-Old Cosmic Mystery

A rare, superluminous supernova located 10 billion light-years away has appeared five times in the sky due to gravitational lensing by two foreground galaxies. Credit: Shutterstock

An extraordinarily rare, gravitationally lensed supernova may offer a powerful new way to measure the universe’s expansion rate.

Astronomers have known for nearly a century that the universe is expanding. What remains uncertain is the exact speed of that expansion. The value, called the Hubble constant, is still fiercely debated and has even raised questions about the standard model of cosmology.

Now, researchers from the Technical University of Munich (TUM), Ludwig Maximilians University (LMU), and the Max Planck Institutes MPA and MPE have captured and analyzed an extraordinarily rare supernova. Their observations may offer a completely independent way to calculate how fast the universe is growing.

The object is a superluminous supernova located about 10 billion light-years from Earth. It shines far brighter than typical stellar explosions. What makes it even more remarkable is how it appears in the sky. Instead of a single point of light, it shows up five times, creating a pattern that resembles cosmic fireworks. This effect is caused by gravitational lensing.

As the supernova’s light travels toward Earth, it passes two massive galaxies in the foreground. Their gravity bends and redirects the light along different routes. Because each path has a slightly different length, the light from each image reaches us at a different time. By carefully measuring these time delays, scientists can determine the present-day expansion rate of the universe.

High-resolution image taken with the Large Binocular Telescope on Mount Graham in Arizona, USA, displaying the two lens galaxies in a warm tone, and the five lensed copies of SN Winny in blue. Credit: SN Winny Research Group

Sherry Suyu, Associate Professor of Observational Cosmology at TUM and Fellow at the Max Planck Institute for Astrophysics, explains: “We nicknamed this supernova SN Winny, inspired by its official designation SN 2025wny. It is an extremely rare event that could play a key role in improving our understanding of the cosmos. The chance of finding a superluminous supernova perfectly aligned with a suitable gravitational lens is lower than one in a million. We spent six years searching for such an event by compiling a list of promising gravitational lenses, and in August 2025, SN Winny matched exactly with one of them.”

High-resolution color image of unique supernova

Gravitationally lensed supernovae are exceptionally uncommon, and only a small number have been used for this kind of measurement. The reliability of the results depends on how precisely astronomers can calculate the masses of the galaxies bending the light. The mass determines how strongly the light is deflected.

To refine those measurements, researchers from MPE and LMU used the Large Binocular Telescope in Arizona, USA. Equipped with two 8.4 meter mirrors and an adaptive optics system that corrects for atmospheric distortion, the telescope delivered extremely sharp images. The team produced the first high-resolution color image of this system published so far.

The images show the two lensing galaxies at the center, surrounded by five bluish images of the same supernova, reminiscent of an exploding firework. This arrangement is unusual because galaxy-scale lens systems typically create only two or four images. Using the precise positions of all five images, Allan Schweinfurth (TUM) and Leon Ecker (LMU), junior members of the research team, developed the first detailed model of how mass is distributed in the lensing galaxies.

“Until now, most lensed supernovae were magnified by massive galaxy clusters, whose mass distributions are complex and hard to model,“ says Allan Schweinfurth. “SN Winny, however, is lensed by just two individual galaxies. We find overall smooth and regular light and mass distributions for these galaxies, suggesting that they have not yet collided in the past despite their close apparent proximity. The overall simplicity of the system offers an exciting opportunity to measure the universe’s expansion rate with high accuracy.”

Two methods, two very different results

Until now, most measurements of the Hubble constant have relied on two main techniques, and they do not agree. This disagreement is known as the Hubble tension.

The first approach focuses on the relatively nearby universe. Astronomers measure distances to galaxies step by step, similar to climbing a ladder, which is why it is called the cosmic distance ladder. They use objects with well-known brightness to determine distances and then compare those distances with how fast galaxies are moving away from us. Because this technique involves multiple stages of calibration, even small uncertainties can build up and influence the final value.

The second method looks back to the early universe. It analyzes the cosmic microwave background, the faint radiation left over from the Big Bang, and applies models of cosmic evolution to estimate the current expansion rate. While this method produces highly precise results, it depends strongly on assumptions about how the universe has changed over billions of years, and those assumptions remain under discussion.

A new, one-step approach to Hubble constant

A third strategy now offers an independent alternative: studying a gravitationally lensed supernova. Stefan Taubenberger, a key member of Professor Suyu’s team and first author of the supernova-identification study, explains that measuring the time delays between the multiple images, combined with an accurate model of the lensing galaxy’s mass distribution, allows researchers to directly determine the Hubble constant: “Unlike the cosmic distance ladder, this is a one-step method, with fewer and completely different sources of systematic uncertainties.”

Astronomers around the world are continuing to monitor SN Winny using both ground-based and space-based telescopes. The data they collect could provide valuable new evidence and help resolve one of the most persistent disagreements in modern cosmology.

References:

“HOLISMOKES XIX: SN 2025wny at z=2, the first strongly lensed superluminous supernova” by Stefan Taubenberger, Ana Acebron, Raoul Cañameras, Ting-Wan Chen, Aymeric Galan, Claudio Grillo, Alejandra Melo, Stefan Schuldt, Allan G. Schweinfurth, Sherry H. Suyu, Greg Aldering, Amar Aryan, Yu-Hsing Lee, Elias Mamuzic, Martin Millon, Thomas M. Reynolds, Alexey V. Sergeyev, Ildar M. Asfandiyarov, Stéphane Basa, Stéphane Blondin, Otabek A. Burkhonov, Lise Christensen, Frederic Courbin, Shuhrat A. Ehgamberdiev, Tom L. Killestein, Seppo Mattila, Asadulla M. Shaymanov, Yiping Shu, Dong Xu, Sheng Yang, Daniel Gruen, Justin D. R. Pierel, Christopher J. Storfer, Kim-Vy Tran, Kenneth C. Wong, Rosa L. Becerra, Damien Dornic, Jean-Grégoire Ducoin, Noémie Globus, Claudia P. Gutiérrez, Ji-an Jiang, Hanindyo Kuncarayakti, Diego López-Cámara, Peter Lundqvist, Francesco Magnani, Enrique Moreno Méndez, Benjamin Schneider and Christian Vogl, 24 October 2025, arXiv.
DOI: 10.48550/arXiv.2510.21694

“HOLISMOKES XX. Lens models of binary lens galaxies with five images of Supernova Winny” by L. R. Ecker, A. G. Schweinfurth, R. Saglia, L. Deng, S. H. Suyu, C. Saulder, J. Snigula, R. Bender, R. Cañameras, T.-W. Chen, A. Galan, A. Halkola, E. Mamuzic, A. Melo, S. Schuldt and S. Taubenberger, 18 February 2025, arXiv.
DOI: 10.48550/arXiv.2602.16620

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