Scientists have known for nearly a century that the universe is expanding, but the precise rate of that expansion remains to be uncertain. This ongoing debate has even raised questions on the usual 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 a particularly rare variety of supernova that might provide a brand new and independent method to measure how briskly the universe is growing.
The article at the middle of this discovery is a superluminous supernova positioned about 10 billion light-years away. It shines much brighter than typical stellar explosions. What makes it especially remarkable is the way it appears within the sky. As a substitute of a single point of sunshine, it shows up five separate times, making a striking cosmic display brought on by gravitational lensing.
Because the supernova’s light travels toward Earth, it passes by two galaxies within the foreground. Their gravity bends the sunshine and sends it along multiple paths. Because each path is barely different in length, the sunshine from each image arrives at different times. By rigorously measuring these delays, scientists can calculate the present expansion rate of the universe, often known as the Hubble constant.
Sherry Suyu, Associate Professor of Observational Cosmology at TUM and Fellow on the Max Planck Institute for Astrophysics, explains: “We nicknamed this supernova SN Winny, inspired by its official designation SN 2025wny. It’s a particularly rare event that might play a key role in improving our understanding of the cosmos. The prospect of finding a superluminous supernova perfectly aligned with an acceptable gravitational lens is lower than one in one million. We spent six years trying to find such an event by compiling a listing of promising gravitational lenses, and in August 2025, SN Winny matched exactly with one among them.”
High-resolution imaging reveals a novel system
Gravitationally lensed supernovae are extremely unusual, which suggests only a small variety of these measurements have been made thus far. Their reliability depends heavily on how accurately scientists can determine the masses of the galaxies bending the sunshine, since those masses control the strength of the lensing effect.
To enhance 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 primary high-resolution color image of this method.
The image shows two lensing galaxies at the middle, surrounded by five bluish points of sunshine that represent the supernova’s multiple images. This configuration is unusual, since most similar systems produce only two or 4 images. By analyzing the positions of all five images, Allan Schweinfurth (TUM) and Leon Ecker (LMU), junior members of the team, created the primary detailed model of how mass is distributed within 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, nevertheless, is lensed by just two individual galaxies. We discover overall smooth and regular light and mass distributions for these galaxies, suggesting that they’ve not yet collided prior to now despite their close apparent proximity. The general 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 depend on two important approaches to measure the Hubble constant, but they don’t agree with one another. This disagreement is often known as the Hubble tension.
One method focuses on nearby galaxies and builds up distance measurements step-by-step, much like climbing a ladder. Because each step depends upon the previous one, this approach is named the cosmic distance ladder. It uses objects with known brightness to estimate distances, then compares those distances to how briskly galaxies are moving away. Nevertheless, since it involves many calibration steps, small uncertainties can construct up and affect the end result.
The second method looks on the early universe by studying the cosmic microwave background, the faint radiation left over from the Big Bang. Using models of how the universe evolved, scientists can calculate the present expansion rate. While this method could be very precise, it depends heavily on assumptions in regards to the universe’s history, that are still being examined and debated.
A brand new one-step method to measure the Hubble constant
A 3rd technique is now emerging based on gravitationally lensed supernovae like SN Winny. Stefan Taubenberger, a key member of Professor Suyu’s team and lead writer of the supernova identification study, explains that measuring the time delays between the multiple images, combined with knowledge of the lensing galaxies’ mass, allows scientists to directly determine the Hubble constant: “Unlike the cosmic distance ladder, it is a one-step method, with fewer and completely different sources of systematic uncertainties.”
Astronomers world wide are continuing to watch SN Winny using each ground-based and space-based telescopes. These observations are expected to supply essential recent data that might help resolve the long-standing disagreement over how briskly the universe is expanding.