This supernova has five faces and could solve a cosmic mystery

One explosion, two galaxies, five images

Astronomers were able to observe a rare spectacle. A distant supernova, named SN 2025wny or more commonly “SN Winny,” appeared not once, but five times in the telescopes’ field of view. What caused this phenomenon? The light from the explosion was bent by the gravitational pull of two galaxies in the foreground, creating five distinct images of the event.

This multiplication of images is not merely an optical curiosity. Each image of the supernova lights up with a slight time delay relative to the others. By precisely measuring these delays, scientists hope to calculate the rate at which the universe is expanding today. A high-resolution color image has made it possible to clearly visualize this configuration: the five bright spots of SN 2025wny encircling the pair of galaxies that act as a cosmic lens.

Dr. Sherry Suyu and her team at the Technical University of Munich (TUM) have documented the exact positions of these multiple images, confirming that the system is ideally configured for timing measurements. The arrangement is unusually clear, with two individual galaxies producing five sharp copies, whereas astronomers more commonly observe two or four images. This simplicity places the main focus on measuring the time shifts between the images—a crucial step in translating this cosmic geometry into a concrete value for the universe’s expansion rate.

The Magic of Gravitational Lensing

How is such a phenomenon possible? As the light from SN Winny traveled toward Earth, the gravity of two galaxies in its path bent its trajectory. This effect, known as gravitational lensing, occurs when very massive objects deflect and amplify light from more distant sources. The light is then forced to take several different paths to reach us.

Each of these optical paths covers a slightly different distance, causing delays in the arrival of the light. For SN 2025wny, these time delays are estimated to range from a few days to a few weeks. Measuring these differences with high precision allows us to translate the time delays into an estimate of the Hubble constant, which represents the current rate of expansion of the universe per unit of distance.

The presence of a fifth image further strengthens the analysis. Each bright spot helps map the gravitational field of the foreground galaxies from a different angle. The updated lensing models match the observed positions perfectly and confirm that this additional spot does indeed belong to SN Winny. This tightens the constraints on the system’s mass and geometry, making the model more robust.

Portrait of an Extraordinary Explosion

The explosion itself is anything but ordinary. Measurements of its light have classified it as a superluminous supernova. This is a stellar explosion much brighter than normal, making it visible even at prodigious distances. The light from SN 2025wny traveled for more than 10 billion years before reaching us, but the gravitational lensing effect kept it bright enough to be studied by today’s telescopes.

Since much of its light is emitted in the ultraviolet spectrum, the team was able to match it to rare Type I superluminous supernovae observed at similar distances. The distance of the event is thus confirmed: more than 10 billion light-years separate this explosion from our planet. It is this extreme brightness that makes the phenomenon so valuable to cosmologists.

At the Heart of the “Hubble Tension”

This discovery comes amid a bustling scientific landscape marked by what cosmologists call the “Hubble tension.” This refers to a persistent discrepancy between two estimates of the universe’s expansion rate. The first method relies on observations of nearby galaxies, using pulsating stars to calibrate supernovae that serve as distance markers and allow the expansion rate to be deduced from their recession velocities.

The second estimate comes from data collected by the Planck satellite, which mapped the faint microwave radiation in the sky—the famous cosmic microwave background. This approach relies on a comprehensive cosmological model to predict the current expansion rate. The problem is that the two values do not agree. The time measurements of SN Winny, obtained using a completely independent method, allow both approaches to be tested simultaneously.

Instead of going through numerous calibration steps, the gravitational lensing delay method directly links the expansion rate to geometry and time within a single system. It thus introduces new sources of potential error, rather than recycling those from traditional methods, offering a fresh perspective on the problem.

Constant Monitoring

The work has only just begun. To measure the delays, astronomers must track the brightness variations of each image over the course of several months. Nightly monitoring is therefore underway to record how the light fades and then reappears. Frequent observations using multiple telescopes have already made it possible to construct a clear light curve for the brightest image, and this effort is now being extended to the fainter images.

The observation presents a technical challenge. On Mount Graham in Arizona, the Large Binocular Telescope provided the necessary sharpness. An adaptive optics system—equipment that corrects for blurring caused by Earth’s atmosphere—allowed the team to separate the light from the galaxies from that of nearby supernova images. Better separation reduces the uncertainty in the lens’s mass, a key factor in determining the duration of each light path. Space observatories, which are free from atmospheric blurring, are also being utilized.

Another challenge lies in microlensing: the additional bending of light caused by individual stars within foreground galaxies. This phenomenon can alter brightness and complicate the measurement of time delays. Despite these obstacles, once the time delays are measured, the same lensing models can convert them into an estimate of the Hubble constant.

A Rare and Promising Discovery

To date, the number of supernovae significantly affected by gravitational lensing remains very low. Each new discovery therefore carries considerable weight. As Dr. Suyu points out, “The chance of finding a super-luminous supernova perfectly aligned with a suitable gravitational lens is less than one in a million.” SN Winny’s extreme brightness and slow evolution made it easier to detect, especially since the distance and the lensing effect stretched out the duration of the event.

If scientists manage to find enough similar systems, this new way of measuring the expansion of the universe could finally settle the question: Does the current discrepancy point to new physics or to hidden errors in existing methods? SN Winny combines a rare stellar explosion, a clear gravitational lens, and the promise of precise timing measurements, offering an approach that stands apart from traditional methods.

The study was published in the journal Astronomy & Astrophysics. If continuous monitoring yields precise time measurements and the lensing models remain stable, the result could resolve the debate over the expansion of the universe with a definitive figure.

Source: earth.com

This supernova has five faces and could solve a cosmic mystery