BERLIN — A supernova that exploded roughly 10 billion light‑years away and whose light has been split into five separate images may provide an independent measurement of the universe’s expansion rate, potentially easing the long‑standing “Hubble tension.” The phenomenon, dubbed SN Winny, was identified after six years of searching by teams from the Technical University of Munich, Ludwig Maximilian University, and the Max Planck Institutes. The Hubble constant, which quantifies how fast space expands, can be derived in two principal ways.
One approach analyses the cosmic microwave background—the afterglow of the Big Bang—while the other builds a “distance ladder” using nearby exploding stars. Both methods are built on extensive data and decades of refinement, yet they yield conflicting values, leaving cosmologists uncertain whether the discrepancy stems from unknown systematic errors or from physics beyond the current model. SN Winny presents a third, purely geometric technique. As its photons traveled toward Earth, they passed close to two massive foreground galaxies.
The intense gravity of these galaxies warped spacetime, bending the light and creating five distinct paths of different lengths. Because light travels at a constant speed, each path results in a separate arrival time, producing five observable copies of the same explosion—much like echoes of a single clap.
The intervals between the five images are the crucial data. By measuring these time delays and modeling the mass distribution of the intervening galaxies, researchers can directly calculate the Hubble constant for the epoch when the supernova exploded, without invoking early‑universe physics or local distance calibrations. This yields a value that reflects the expansion rate about 10 billion years ago, offering a midpoint between the early‑universe and local measurements.
The odds of encountering such an ideal alignment are exceedingly slim—estimated at less than one in a million. Yet the collaborative effort persisted, and the discovery of SN Winny now opens a pathway to test whether the Hubble constant truly varies over cosmic time or whether one of the existing methods contains hidden biases.
Three outcomes are possible once the delays are precisely measured and the lens model refined. If the derived constant aligns with the cosmic‑microwave‑background result, the discrepancy would point to an error in the local distance‑ladder technique. Conversely, agreement with the local measurement would challenge aspects of the standard cosmological model that predict the early‑universe value.
A result that falls between or outside both established values could signal the need for new physics or a revision of the current framework. Beyond its immediate cosmological implications, SN Winny exemplifies the power of gravitational lensing as a tool for precision astronomy.
The simple physics—light’s fixed speed combined with spacetime curvature—allows astronomers to translate observed time delays into a direct probe of cosmic expansion, bypassing many of the assumptions required by other methods. With the supernova now identified, the next phase involves detailed monitoring of the five images to capture the exact delay intervals, followed by sophisticated modeling of the lensing galaxies’ mass distribution. The outcome will either reinforce one of the existing Hubble constant determinations or carve out a new, independent value that could help reconcile the long‑standing tension.
In essence, SN Winny is not merely a rare astronomical curiosity; it is a potential key to testing the consistency of the standard cosmological model across billions of years. As the universe’s own geometry provides the measurement, the result will carry weight in the ongoing debate over how we understand cosmic expansion.
