A remarkable discovery has emerged from the depths of space, centering on a superluminous supernova located approximately 10 billion light-years away. This extraordinary stellar explosion, known as SN Winny, shines with an intensity far exceeding that of typical supernovae. What sets this cosmic phenomenon apart is its unique appearance; rather than manifesting as a single point of light, it is observed five distinct times in the night sky, a spectacular effect attributed to gravitational lensing.
As the light from SN Winny journeys toward Earth, it encounters two foreground galaxies whose gravitational forces bend the light, creating multiple pathways. Each path varies slightly in length, resulting in the light reaching us at different intervals. By meticulously measuring these time delays, scientists can derive the current expansion rate of the universe, known as the Hubble constant.
Sherry Suyu, an Associate Professor of Observational Cosmology at TUM and a Fellow at the Max Planck Institute for Astrophysics, notes, "We affectionately call this supernova SN Winny, derived from its official designation SN 2025wny. The likelihood of finding a superluminous supernova perfectly aligned with an appropriate gravitational lens is less than one in a million. After six years of investigation and compiling a list of potential gravitational lenses, we finally found the perfect match in August 2025."
High-Resolution Imaging Unveils a Unique Cosmic System
Gravitationally lensed supernovae are exceedingly rare, resulting in limited measurements thus far. The precision of these measurements heavily relies on accurately determining the masses of the galaxies responsible for the lensing effect.
To enhance these measurements, researchers from MPE and LMU utilized the Large Binocular Telescope in Arizona, USA. This advanced telescope, featuring two 8.4-meter mirrors and an adaptive optics system to mitigate atmospheric distortion, produced the first high-resolution color image of the system.
The resulting image showcases two lensing galaxies at the center, encircled by five bluish points of light representing the supernova's multiple appearances. This configuration is quite rare, as most similar systems typically yield only two to four images. By analyzing the positions of these five images, team members Allan Schweinfurth (TUM) and Leon Ecker (LMU) developed the first detailed model of mass distribution within the lensing galaxies.
"Previously, most lensed supernovae were magnified by massive galaxy clusters, which present complex mass distributions that are challenging to model," explains Schweinfurth. "In contrast, SN Winny is lensed by just two individual galaxies, revealing smoother light and mass distributions, indicating they have not collided despite their close proximity. This simplicity offers an exciting opportunity for highly accurate measurements of the universe's expansion rate."
Emerging Techniques for Measuring the Hubble Constant
Astronomers currently employ two primary methods to measure the Hubble constant, which have led to a discrepancy known as the Hubble tension. One method, the cosmic distance ladder, involves stepwise distance measurements using objects with known brightness. The second approach examines the cosmic microwave background radiation from the early universe. However, a new technique is evolving, leveraging gravitationally lensed supernovae like SN Winny to provide a direct measurement of the Hubble constant.
Stefan Taubenberger, a prominent member of Suyu's team, emphasizes that measuring time delays between the multiple images, paired with knowledge of the lensing galaxies' mass, allows for a straightforward determination of the Hubble constant. This method reduces systematic uncertainties, offering a promising path forward.
As astronomers globally continue to observe SN Winny with both ground-based and space telescopes, the insights gained could play a pivotal role in resolving the longstanding debate regarding the universe's expansion rate, potentially reshaping our understanding of cosmic evolution.