A one-in-a-million supernova seen five times could reveal the Universe’s true speed
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A one-in-a-million supernova seen five times could reveal the Universe’s true speed
A once-in-a-million “cosmic fireworks” supernova could finally reveal how fast the universe is expanding.
Date:
April 29, 2026
Source:
Technical University of Munich (TUM)
Summary:
A spectacular cosmic event nicknamed “SN Winny” could help solve one of astronomy’s biggest mysteries: how fast the universe is expanding. This rare superluminous supernova, located 10 billion light-years away, appears five times in the sky thanks to gravitational lensing, creating a dazzling “cosmic fireworks” effect. By measuring the slight delays between each appearance—caused by light taking different paths around two foreground galaxies—scientists can directly calculate the universe’s expansion rate.
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A rare supernova appearing five times in the sky is offering a powerful new way to measure the universe’s expansion. By tracking the timing differences between these cosmic echoes, scientists may finally resolve the long-standing Hubble tension. Credit: AI/ScienceDaily.com
Scientists have known for nearly a century that the universe is expanding, but the exact rate of that expansion is still uncertain. This ongoing debate 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 identified and analyzed an extremely rare type of supernova that could provide a new and independent way to measure how fast the universe is growing.
The object at the center of this discovery is a superluminous supernova located about 10 billion light-years away. It shines much brighter than typical stellar explosions. What makes it especially remarkable is how it appears in the sky. Instead of a single point of light, it shows up five separate times, creating a striking cosmic display caused by gravitational lensing.
As the supernova's light travels toward Earth, it passes by two galaxies in the foreground. Their gravity bends the light and sends it along multiple paths. Because each path is slightly different in length, the light from each image arrives at different times. By carefully measuring these delays, scientists can calculate the current expansion rate of the universe, known as the Hubble constant.
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 imaging reveals a unique system
Gravitationally lensed supernovae are extremely uncommon, which means only a small number of these measurements have been made so far. Their reliability depends heavily on how accurately scientists can determine the masses of the galaxies bending the light, since those masses control the strength of the lensing effect.
To improve 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 reduces atmospheric distortion, the telescope produced the first high-resolution color image of this system.
The image shows two lensing galaxies at the center, surrounded by five bluish points of light that represent the supernova's multiple images. This configuration is unusual, since most similar systems produce only two or four images. By analyzing the positions of all five images, Allan Schweinfurth (TUM) and Leon Ecker (LMU), junior members of the team, created 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
Currently, astronomers rely on two main approaches to measure the Hubble constant, but they do not agree with each other. This disagreement is known as the Hubble tension.
One method focuses on nearby galaxies and builds up distance me