The Supernova That Split Into Four

Introduction: When One Star Died Four Times

Astronomers have recently witnessed an event so improbable that it reads like a misprint in the fabric of spacetime: a single superluminous supernova, designated SN 2025wny, appearing as four distinct points of light in the sky, arranged in a perfect gravitational mandala.[1] Each point is the same explosion, seen along a different bent path through the universe—four delayed echoes of one titanic death.[1]

This is the first known gravitationally lensed superluminous supernova, and the first supernova of any type whose multiple images are cleanly resolved from the ground under ordinary observing conditions.[1] Its light has travelled for over 10 billion years, originating when the universe was less than a quarter of its current age, then being split and magnified by a massive intervening galaxy.[1]

Beyond its visual strangeness, SN 2025wny offers something coveted: a new way to measure the expansion rate of the universe and to interrogate the elusive dark energy that appears to drive that expansion.[1][3] As cosmologists struggle with the growing “Hubble tension” between different measurements of cosmic expansion, this fourfold star may become one of the most incisive tools in their arsenal.[2][3]

Cosmic Background: A Hall of Mirrors in an Expanding Universe

To understand why SN 2025wny matters, it helps to recall three intertwined ideas: superluminous supernovae, gravitational lensing, and the Hubble constant.

  • Superluminous supernovae (SLSNe) are rare stellar explosions tens to hundreds of times brighter than typical core‑collapse or Type Ia supernovae.[1] They are so luminous that, in principle, they can be seen across much of the observable universe.

  • Gravitational lensing occurs when mass—such as a galaxy or cluster—bends spacetime strongly enough that light from a more distant object is deflected and magnified, sometimes producing multiple images.[1][3] In the special case where four images appear in a cross‑like pattern around the lensing galaxy, astronomers call the configuration an Einstein cross.[1]

  • The Hubble constant (H₀) describes how fast the universe is expanding today. Measurements from the early universe (cosmic microwave background) and the late universe (nearby supernovae and other distance indicators) increasingly disagree, a discrepancy known as the Hubble tension.[2][3] New, independent methods of determining H₀ are desperately sought to decide whether new physics is required.

Recent work with gravitationally lensed quasars, where the variable brightness of the background quasar is seen at different times along different lensed paths, has shown that time delays between the images can be turned into a one‑step measurement of H₀.[2][3] Now, SN 2025wny extends this technique from steadily accreting black holes to a brief, precisely‑timed stellar catastrophe.

The Discovery: A Routine Sky Patrol Finds an Impossible Beacon

SN 2025wny did not reveal itself with fanfare. It began as an unassuming alert from the Zwicky Transient Facility (ZTF) in California, a survey telescope that scans the sky nightly for short‑lived or changing objects.[1]

  • On August 29, 2025, ZTF flagged a new source, with earlier images showing a faint precursor just two days before.[1]
  • Almost simultaneously, the Gravitational-wave Optical Transient Observer (GOTO) reported the same event, underscoring how modern surveys can converge quickly on emerging transients.[1]

What first drew attention was not the brightness alone, but its location. The newborn point of light hovered near a massive red galaxy whose distance—expressed as a redshift of 0.375—had already been pinned down by the Dark Energy Spectroscopic Instrument (DESI).[1] If the supernova were physically associated with that galaxy, its observed brightness would have been wildly inconsistent with any known type of explosion.[1]

Instead, astronomers suspected a more exotic geometry:

  • The foreground galaxy might be acting as a gravitational lens.
  • The true host of the supernova would then be a more distant background galaxy, its light magnified and split on its way to Earth.[1]

Cross‑checks with the Strong Lensing Database strengthened the case, as this region had already been flagged as a lens candidate.[1] Archival images from the Legacy Survey and the Canada–France–Hawaii Telescope revealed four blue images of a remote galaxy arranged in a cross around two red galaxies—a pre‑existing gravitational stage awaiting a transient actor.[1]

When the Liverpool Telescope was trained on the object, early images showed only a single bright point.[1] As the weeks passed and observing conditions improved, data reduction revealed three clear points and a fourth fainter one, positioned exactly where the four lensed galaxy images had been seen before.[1] The inescapable conclusion:

One supernova. Four apparent suns. A natural laboratory carved out by gravity itself.

The Physics: Gravity’s Prism and an Over‑Bright Star

SN 2025wny sits at a redshift of 2.010, meaning its light has travelled more than 10 billion years before arriving at Earth.[1] At such a distance, even a superluminous supernova would usually be too faint to dissect in detail from the ground.

The lensing galaxy at redshift 0.375 changes everything.[1] Its mass curves spacetime so steeply that:

  • The light from the distant host galaxy and its exploding star is bent into four separate paths.
  • These paths intersect our telescopes at four distinct angles, forming an Einstein cross around the lens.[1]
  • Each path has a different length and traverses slightly different gravitational potentials, so the light from each image arrives at a different time—a built‑in cosmic stopwatch.[1]

Even before lensing corrections, the supernova’s ultraviolet brightness was anomalous. After accounting for distance but not magnification:

  • SN 2025wny appeared extraordinarily luminous in the UV, challenging existing models of SLSNe.[1]
  • Astrophysicist Daniel Perley and colleagues outlined three broad possibilities:
    • The lensing magnification is extreme—perhaps a factor of 20 to 50 or more.[1]
    • The event is intrinsically unusually bright in the UV compared with known SLSNe.[1]
    • We are seeing the supernova at a particularly early, hot phase that has rarely been captured in such detail, hinting that many SLSNe may be more UV‑luminous early on than previously recognized.[1]

Untangling which combination of these explanations is correct will require long‑term monitoring and intricate lens modelling, but even the uncertainty is valuable. It forces theorists to revisit their assumptions about:

  • The energy budget and powering mechanisms of SLSNe.
  • The structure and orientation of the lensing galaxy.
  • The statistical likelihood of such extreme magnifications in current and future surveys.

A New Cosmological Ruler: Time Delays and the Hubble Tension

The cosmological significance of SN 2025wny lies in its time structure. Because each lensed image corresponds to light that has travelled along a slightly different path through the cosmic web, the brightness of the four points does not rise and fall in unison.[1] Minute differences in:

  • Path length, and
  • The gravitational potential encountered along those paths

translate into measurable time delays between the light‑curve peaks of each image.[1]

In gravitationally lensed quasars, such time delays have already been exploited by projects like TDCOSMO and related collaborations.[2][3] There, the stochastic flickering of accretion disks around supermassive black holes provides a naturally variable signal whose echoes arrive at different times. By combining these delays with precise mass models of the lensing galaxy, researchers can infer cosmological distances and thus H₀, nearly independent of traditional distance ladders.[2][3]

Recent analyses of lensed quasars have delivered “late universe” Hubble constant values that align with local supernova measurements but clash with early‑universe inferences from the cosmic microwave background, deepening the Hubble tension and suggesting that the discrepancy is not a mere artifact of one technique.[2][3]

SN 2025wny extends this framework into new territory:

  • Unlike quasars, supernovae have well‑defined, single‑shot light curves with sharp features that can be timed precisely.
  • A superluminous event at high redshift, especially one magnified by lensing, yields a clean, high‑signal light curve in all four images.[1]
  • Time delays between images can be linked directly to cosmological distances, underpinned by independent lens mass constraints from spectroscopy and imaging of the lens galaxy and host.[1][3]

If the derived H₀ from SN 2025wny’s time delays matches the lensed quasar results, it will further solidify the case that late‑universe expansion is faster than what early‑universe physics alone predicts.[2][3] If it diverges, it may point to systematic biases specific to either quasars or supernovae—or to more intricate behaviour in dark energy.

Experts Weigh In: A Laboratory for Dark Energy

Astrophysicist Daniel Perley, a reader at Liverpool John Moores University and a leading figure in the follow‑up of SN 2025wny, emphasized how unprecedented the system is:

“No one has found a supernova like this before, and the nature of the system means it may be able to help solve some big problems in astrophysics, such as the nature of the force that drives the expansion of the universe.”[1]

His remark is not hyperbole. Dark energy, often modelled as Einstein’s cosmological constant, is under intense scrutiny. Recent work has raised the possibility that the data may be better explained if dark energy evolves over time, potentially tied to exotic fields such as ultra‑light axion‑like particles.[3]

Studies of evolving dark energy models show that they can, in some scenarios, ease the tension between early‑ and late‑universe measurements—but only within tight constraints.[3] Every new, independent measurement of H₀ and distance–redshift relations adds a crucial piece to this puzzle.

At the same time, a separate line of research uses time delays in gravitationally lensed quasars to test cosmological models.[2][3] A recent analysis employing updated lens modelling techniques reports H₀ values that reinforce the existence of genuine Hubble tension, rather than merely statistical noise or modelling artifacts.[2][3]

By introducing lensed supernovae into this ecosystem, SN 2025wny creates a bridge between:

  • Local distance ladder calibrations using nearby supernovae.
  • High‑redshift superluminous events visible across cosmic time.
  • Gravitational lensing–based cosmography with quasars and galaxies.

In effect, it transforms a single dying star into an instrument for cross‑validating cosmic measurements that were previously only loosely connected.

Alternative Views and Open Questions

While excitement around SN 2025wny is high, several points of caution and contention remain, reflecting the complexity of the underlying physics.

  • Lens modelling degeneracies: Deriving H₀ from time delays is notoriously sensitive to details of the lens mass distribution and to line‑of‑sight structures. Different assumptions about the mass profile of the lens galaxy can yield different inferred values of H₀.[2][3] Critics argue that unless these degeneracies are tightly controlled, lensed systems might not provide as clean a cosmological probe as advertised.

  • Supernova standardization: Unlike Type Ia supernovae, which have been honed into relatively well‑behaved “standard candles,” superluminous supernovae exhibit significant diversity in light‑curve shapes and intrinsic luminosities.[1][3] Some researchers question whether SLSNe can ever be standardized to the precision required for precision cosmology, while others contend that lensing plus time delays sidestep the need for perfect standard candles, relying instead on geometry and general relativity.

  • Dark energy models: Advocates for evolving dark energy or alternative gravity theories see SN 2025wny as a potential arbiter, but it is equally plausible that additional complexity will only expand the parameter space rather than pinpoint a simple resolution.[3] It is conceivable that the Hubble tension could stem from a combination of small systematics and subtle new physics, a scenario that would demand a broad portfolio of independent probes—including events like SN 2025wny.

Despite these debates, there is broad agreement on one point: more such systems are needed. A single fourfold supernova can demonstrate feasibility and hint at answers, but only a population of lensed supernovae, spanning different redshifts and lens configurations, can transform this technique into a precision cosmological tool.

Broader Implications: From Hidden Galaxies to the Fate of the Cosmos

Beyond the Hubble constant, SN 2025wny offers several far‑reaching implications for astrophysics and cosmology.

  • Microscale mapping of distant galaxies: The immense magnification provided by the lens turns the host galaxy into an unusually bright, spatially stretched target.[1] This allows astronomers to probe the star‑forming regions and interstellar medium of a tiny, high‑redshift galaxy that would otherwise be invisible or unresolved. In some cases, such lenses act as cosmic telescopes, revealing sub‑kiloparsec structure in the early universe.

  • Testing the physics of extreme explosions: If SN 2025wny is confirmed to be intrinsically brighter or hotter in the UV than standard SLSNe, models of their power sources—whether magnetar spin‑down, interaction with dense circumstellar material, or pair‑instability mechanisms—will need recalibration.[1] Lensing boosts the signal enough to discriminate between subtle features in the light curve and spectrum that would otherwise be lost.

  • Calibration of next‑generation surveys: Upcoming facilities, such as the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST), are expected to discover millions of transients and vast numbers of strong gravitational lenses.[3] SN 2025wny serves as an early proof of concept for what will become increasingly common: multi‑image, time‑delayed transients sprinkled across survey data. Understanding this system now will guide search algorithms, follow‑up strategies, and cosmological analyses in the decade ahead.[3]

  • Refining dark energy constraints: As other probes—galaxy clustering, weak lensing, baryon acoustic oscillations—tighten the allowed parameter space for dark energy’s behaviour, lensed supernovae will add orthogonal constraints. Should multiple systems like SN 2025wny consistently favor a particular class of models—static cosmological constant, slowly evolving field, or more exotic alternatives—they will help decide the long‑term fate of cosmic expansion: gentle acceleration, runaway expansion, or eventual slowdown.[3]

In this way, the four small points of light mapped by mid‑sized telescopes become levers acting on the largest scales imaginable.

Conclusion: Four Mirrors, One Question

SN 2025wny is more than a photogenic curiosity. It is a 10‑billion‑year‑old question refracted into four simultaneous versions of the sky, each carrying slightly different information about the universe it crossed.[1] By reading the time delays and magnifications etched into those paths, astronomers hope to refine how fast the universe is expanding, how dark energy behaves, and whether our current cosmological model is complete.[1][2][3]

In the coming years, continued monitoring of SN 2025wny and the discovery of additional lensed supernovae will either:

  • Strengthen the case that the Hubble tension is real and demands new physics, or
  • Reveal subtle biases in one or more existing measurement techniques, nudging the data back toward concordance.[2][3]

Either outcome would be profound. For now, the universe has offered a rare and meticulously arranged experiment: a single stellar death, split into four, silently timing our cosmic expansion. The task ahead is as straightforward as it is daunting—measure carefully, model honestly, and listen to what those four echoes say about the shape of everything.