magnetar

Some of the most extreme explosions in the universe are Type I superluminous supernovae. “They are one of the brightest explosions in the Universe,” says Joseph Farah, an astrophysicist at the University of California, Santa Barbara. For years, astrophysicists tried to understand what exactly makes superluminous supernovae so absurdly powerful. Now it seems like we may finally have some answers.

Farah and his colleagues have found that these events are most likely powered by magnetars, rapidly spinning neutron stars that warp the very space and time around them.

The power within

Magnetars have been a leading candidate for the engine behind superluminous supernovae. The theory says these insanely magnetized stars are born from the collapsing core of the original progenitor star and emit energy via magnetic dipole radiation. “This core is roughly a one solar mass object that gets crushed down to the size of a city,” Farah explains. As its spin slows down, a magnetar bleeds its rotational energy into the expanding material of the dead star, lighting it up.

The problem was that this theory did not quite explain observations. In a standard magnetar model, the light curve of the supernova should rise rapidly and then fade away evenly as the neutron star loses its rotational energy. “This way the light curve, in the prediction of this model, just goes up and then down quite smoothly,” Farah says. But when astronomers observe superluminous supernovae, they almost never see this smooth fade. Instead, they see bumps, wiggles, and strange modulations. The light curve flickers over months.

For a while, scientists tried to patch the magnetar engine theory to fit observations. Maybe the expanding debris was slamming into irregular shells of material shed by the star before it died. Or perhaps the magnetar engine was spitting out random, violent flares. But these explanations required highly specific, fine-tuned parameters to match what we were seeing through our telescopes.

The solution to the strange flickering problem came when the Liverpool Gravitational Wave Optical Transient Observer collaboration detected an object designated SN 2024afav on December 12, 2024. Initially, the object looked like a standard superluminous supernova. “It was as bright and it had bumps in the light curve like many other objects of this kind,” Farah says. But as the telescopes kept watching, it started doing something unprecedented: It started to chirp.

The chirping star

In physics, a chirp refers to a signal with a frequency that steadily increases over time. In the case of SN 2024afav, its emissions were bumping up and down, but the gap between these bumps was shrinking. After a second and third bump both appeared with the gaps between them reduced by roughly 35 percent, Farah and his team realized they could calculate how much the gap between the bumps would decrease next.

The team adjusted their observation schedule, pointed their instruments at SN 2024afav, and discovered the fourth bump appeared exactly when they expected it would. The fifth bump enabled the scientists to narrow down the period reduction to about 29 percent.

The fact that Farah and his colleagues could accurately predict the bumps delivered a massive blow to our existing magnetar models. While a few irregular bumps could be explained away by the supernova ejecta crashing into clouds of gas, it doesn’t explain perfectly timed, cleanly sinusoidal modulations with a steadily decaying period. Random space rubble just doesn’t work that way.

“So, we came up with the new model to describe this behavior,” Farah explains. They proposed a new physical mechanism that relied on the Lense-Thirring effect, otherwise known as frame-dragging. Frame-dragging is a prediction of General Relativity, where a massive spinning object slightly drags the spacetime around with it as it rotates. “We didn’t try this mechanism before because it had never been seen around a magnetar before,” Farah says. But when his team did try it, it turned out to perfectly match what was going on.

The flickering in the superluminous supernovae, Farah hypothesized, was caused by the extreme gravity of a newborn magnetar dragging the very spacetime around it along as it was spinning.

Twisted space

To understand Farah’s Lense-Thirring solution, imagine a bowling ball spinning in a vat of molasses. As the ball rotates, friction drags the sticky fluid along, creating a swirling vortex. According to Einstein’s General Relativity, mass and energy can warp the fabric of spacetime, so if a sufficiently large mass is spinning rapidly, it drags the space-time along in a manner similar to the molasses. Around Earth, this effect is minuscule. But around a newborn magnetar, which is far more massive and spinning hundreds of times a second, spacetime is whipped into a violent, twisting frenzy.

When the progenitor star exploded to create SN 2024afav, it didn’t eject all of its material perfectly. Some of the stellar guts failed to escape and fell back toward the newborn magnetar, forming a small accretion disk around it. Crucially, this disk was misaligned, tilted relative to the rotational axis of the magnetar. Because the disk was tilted in this aggressively twisted spacetime, the Lense-Thirring effect forced the entire disk to wobble, or precess, around the magnetar’s spin axis like a top that was spinning ever more slowly.

As this misaligned disk wobbled, it acted like a giant cosmic lampshade: it periodically blocked, reflected, or redirected the intense radiation and jets spewing from the central magnetar. The high-energy photons emitted by the magnetar had to fight their way through the expanding supernova ejecta, getting reprocessed into optical light and diffusing outward over a span of about 15 days. Observed through our telescopes on Earth, this wobbling disk created a rhythmic fluctuation in the superluminous supernova’s brightness.

After Farah and his colleagues explained the bumps in the signal with the wobbling disk around the magnetar, they moved to explaining why the signal chirped.

The shrinking disk

The answer the team proposes lies in the environment of the disk itself. The size of this accretion disk isn’t static. It’s determined by an inward ram pressure from the infalling matter and the outward radiation pressure coming from the magnetar. Over time, as the exploding star runs out of fallback material, the accretion rate of the disk drops. With less matter pushing in, the disk loses equilibrium and begins to shrink, falling inward toward the magnetar. And the closer it gets to the spinning magnetar, the stronger the Lense-Thirring effect becomes.

As the accretion disk shrinks and falls deeper into the gravity well, the twisted spacetime whips it around faster and faster. “Imagine a pirouetting figure skater pulling her arms in to accelerate the spinning movement,” Farah suggests. In consequence, the precession speeds up, the wobbles get tighter, and the light curve chirps.

Finally, by measuring the chirps, Farah and his colleagues were able to work backward to measure the properties of the magnetar powering the SN 2024afav. They constrained its spin period to 4.2 milliseconds and precisely calculated its staggeringly powerful magnetic field. The team found that the magnetar’s properties that derived solely from the chirping matched the properties required to power the overall baseline brightness of the superluminous supernova. The engine that powered the main explosion was exactly the right size and speed to cause the wobbling we observed.

But the work on the revised “magnetar+LT” model is just beginning. “This object is so rare and so new,” Farah admits. “We were scraping the bottom of the barrel for references that were even remotely related to the idea we were pitching here.”

Superluminous siblings

Farah’s team went back and looked at archival data from other bumpy superluminous supernovae such as SN 2018kyt, SN 2019unb, and SN 2021mkr. They found that their “magnetar+LT” model explains the modulations in those events as well. A whole class of exploding stars that previously required multiple mutually exclusive physical explanations could be unified by a single, elegant model.

This model, though, still has many unanswered questions. “How the accretion disk forms, how it blocks or modulates the light from the magnetar, how that light then gets to the ejecta, and finally how it gets to the observer,” Farah listed. “Basically every step along the way we made the best assumptions we could.” For each of these steps, he admits, there were at least five different ways it could happen, and the team just went with their best guess of what was going on.

To really figure it all out, Farah says, we need to wait till more objects like SN 2024afav are discovered. And this, he hopes, should become possible with new observatories like the Vera C. Rubin Observatory in Chile coming online. “The Rubin Observatory is expected to discover dozens of these chirped supernovae,” Farah says. “We will be able to test our models against many different objects. There’s definitely room for development and growth. This is just the very beginning.”

Nature, 2026. DOI: 10.1038/s41586-026-10151-0