MPE and LMU Scientists Confirm Five-Image Gravitationally Lensed Supernova – Key Step Toward Measuring the Hubble Constant
A rare gravitationally lensed system showing a superluminous supernova in five distinct images has now been definitively characterized. With observations at the Large Binocular Telescope (LBT) in November 2025, scientists from the Max Planck Institute for Extraterrestrial Physics (MPE) and Ludwig-Maximilians-University (LMU) confirmed the existence of the fifth image and laid the foundation for precise cosmological measurements.
Since September 2025, the system SN Winny—a superluminous stellar explosion located 10 billion light-years away—had been identified as a candidate for a strongly lensed supernova. Analysis of images from the Canada-France-Hawaii Telescope (CFHT) had suggested the presence of a fifth image. However, two critical questions remained: Is the fifth image real? And does it represent a genuine copy of the same supernova?
These questions were answered only through observations at the Large Binocular Telescope (LBT) in Arizona in November 2025. A team of MPE and LMU scientists, led by Ralf Bender (director of MPE and LMU Professor) — Leon Ecker, Christoph Saulder, Jan Snigula, — conducted a dedicated observing campaign.
The analysis of 59 sharp near-infrared images, taken with the J and K filters and adaptive optics, was carried out by Roberto Saglia (MPE/LMU). “The results clearly confirm that the fifth image is real and has the same color as the other four,” says Saglia. “The positions of the five SN Winny images are now sufficiently precise to serve as the basis for a detailed mass model.”
Two Galaxies as Lens – A Simple System for Complex Measurements
The system is lensed by two individual galaxies that show no clear signs of past interaction. Their mass distribution is smooth and regular—unlike the complex, difficult-to-model galaxy clusters that typically magnify other lensed supernovae.
“The relative simplicity of this system makes it particularly well-suited for precise cosmological modeling,” says Saglia. “The smooth mass distribution allows for reliable modeling, enabling a high-precision determination of the Hubble constant.”
Mass Model and Future Observations
Leon Eckard in collaboration with Allan Schweinfurth (Master’s student at TUM, supervised by Sherry Suyu from the Technical University Munich and the Max Planck Institute for Astrophysics), determined the total mass of the two lensing galaxies. A combined mass of 600 billion solar masses is required to explain the observed lensing configuration. The supernova is magnified by a factor between 1.5 and 10.
The fully characterized system now enables the measurement of time delays between the five images. These measurements will be crucial for determining the Hubble constant H₀ directly—without relying on the multi-step calibration of the traditional cosmic distance ladder.
Leon Ecker is the first author of the paper submitted to Astronomy & Astrophysics describing these results. Ralf Bender points out that “The Observatory of the LMU group is well-positioned to carry out the necessary follow-up observations, with the Hobby–Eberly Telescope and the Wendelstein Observatory, we already have instruments capable of delivering time-domain data.”
A Rare Event – A Major Contribution
“The chance of finding a superluminous supernova so well aligned with a suitable gravitational lens is on the order of one in a million,” says Leon Ecker. “The fact that this system is one of the few known strongly lensed superluminous supernovae makes it particularly unique. The LBT observations were a decisive step in confirming the fifth image and establishing the foundation for future measurements.”
