The brightest explosions in the universe remain among astronomy's most difficult puzzles. Type I superluminous supernovae outshine ordinary stellar explosions by a factor of ten or more, yet their true power source has eluded explanation for years. A team led by astrophysicist Joseph Farah at the University of California Santa Barbara has now proposed a solution that invokes one of general relativity's most exotic predictions: the dragging of spacetime itself.
Magnetars have long been the leading candidate for powering these extreme events. These rapidly spinning neutron stars possess magnetic fields so intense they warp the fabric of spacetime around them. When a magnetar forms from the collapse of a massive star's core, the theory suggests, it bleeds its rotational energy into the expanding debris, creating a spectacular explosion. Yet observations have never cleanly matched this picture. Standard magnetar models predict a smooth rise and fade in brightness, but astronomers consistently observe irregular bumps and flickering across months.
The breakthrough came in December 2024 when the Liverpool Gravitational Wave Optical Transient Observer collaboration detected a supernova designated SN 2024afav. What began as an ordinary superluminous supernova soon displayed unprecedented behaviour. Its brightness modulations accelerated over time in a pattern physicists call a chirp, where the frequency steadily increases. Farah's team realised they could predict the timing of subsequent brightness peaks with remarkable precision, a consistency that ruled out random collisions with gas clouds or irregular flares from the magnetar.
The explanation involves the Lense-Thirring effect, also known as frame-dragging. According to Einstein's general relativity, a massive spinning object drags the spacetime surrounding it, much as a spinning ball creates swirls in thick fluid. Around a newborn magnetar spinning hundreds of times per second, this effect becomes extreme. When the progenitor star exploded, some of its material fell back toward the magnetar rather than escaping entirely, forming a small misaligned accretion disk. The twisted spacetime forced this tilted disk to wobble and precess like a slowing top, periodically blocking and redirecting radiation from the magnetar. Observed from Earth, this cosmic modulation created the rhythmic brightness fluctuations.
The chirping effect emerges from the disk's evolution. As the exploding star's fallback rate decreases, the disk loses material and shrinks inward toward the magnetar. As it falls deeper into the gravity well, the frame-dragging effect intensifies, much as a figure skater spins faster when pulling in her arms. The disk precesses more rapidly, the wobbles tighten, and the light curve chirps accordingly. By measuring the chirp's properties, Farah's team determined the magnetar's spin period at 4.2 milliseconds and calculated its magnetic field strength with precision previously impossible to achieve.
The research extends beyond SN 2024afav. When the team examined archival observations of other bumpy superluminous supernovae including SN 2018kyt, SN 2019unb and SN 2021mkr, their magnetar-plus-frame-dragging model explained all of them. A diverse collection of extreme events previously requiring multiple incompatible physical explanations now yielded to a single elegant framework. This unification suggests the discovery addresses a genuine feature of superluminous supernova physics rather than describing an isolated anomaly.
The model remains incomplete. Farah acknowledges substantial uncertainties about how the accretion disk forms, exactly how it blocks magnetar radiation, and how that light propagates through the expanding debris to reach observers. Each step involves multiple competing possibilities, and the team selected their best estimates. Future observations should clarify these details. The Vera C. Rubin Observatory in Chile, expected to come online in the coming years, should discover dozens of similar chirped supernovae and allow rigorous testing of the predictions against diverse observations. As Farah notes, this represents merely the beginning of understanding how extreme gravity shapes the universe's most violent explosions.