For the first time, astronomers have found compelling evidence of a magnetar being born inside a supernova. A magnetar is a neutron star with one of the strongest magnetic fields known in nature. Fields of this scale are behind the often-repeated estimate that a magnetar placed halfway between Earth and the Moon could erase magnetic-strip cards on Earth.
Until now, however, astronomers had never identified such a clear observational signature of one forming.
The clue came from a dying star about a billion light-years away. Its explosion, an unusually bright event called SN 2024afav, peaked roughly 50 days after it began and then should have faded relatively smoothly. It did not. Its light dipped and rose, then dipped and rose again, while the gaps between those fluctuations became progressively shorter. Previous explosions of this kind had shown one or two such bumps. This one showed four prominent post-peak bumps, each following the previous one more quickly.
That speeding-up pattern is called a chirp, similar in form to the rising-frequency signal astronomers detect when two black holes spiral together. Coming from a single exploding star, it had no established explanation. Joseph Farah said there was “just no existing model that could explain a pattern of bumps that get faster in time.”
The answer proposed in a study published in Nature on 11 March 2026 was a newborn magnetar hidden inside the expanding remains of the star.
What a magnetar is, and why one had never been caught being born
A magnetar is a type of neutron star: the exceptionally dense collapsed core that can remain after a massive star dies. What sets a magnetar apart is its extreme magnetic field.
These objects are only about ten miles across. The magnetar inferred inside SN 2024afav appears to rotate once every 4.2 milliseconds, or about 238 times per second. The modelling suggests that its magnetic field is roughly 300 trillion times stronger than Earth’s.
Neither of those properties was measured directly. Astronomers inferred them by fitting the supernova’s overall brightness and its accelerating pattern of bumps to a physical model.
The problem had always been visibility. Researchers had suspected for years that newborn magnetars might power some of the brightest supernovae, but the compact star itself would be buried beneath expanding layers of debris. As UC Berkeley theorist Dan Kasen put it, “For years the magnetar idea has felt almost like a theorist’s magic trick — hiding a powerful engine behind layers of supernova debris.”
The engine was thought to be present, but astronomers had lacked a signal that could be clearly connected to its physical properties.
How a wobbling disk could make a chirp
The proposed explanation relies on an effect predicted by Einstein’s theory of general relativity. According to Farah’s model, some material from the explosion fell back towards the newborn magnetar and formed an accretion disk around it.
The disk was probably uneven and tilted, meaning that its axis did not line up with the spin axis of the neutron star beneath it.
A rapidly spinning mass drags the surrounding fabric of spacetime slightly around with it. This phenomenon, known as the Lense–Thirring effect or frame-dragging, can make a tilted disk precess, or wobble, around the magnetar.
As the disk gradually moves inwards, its precession speeds up. That wobbling could periodically block, reflect or redirect radiation from the magnetar, or alter the rate at which material fell onto it. Each cycle would therefore change how much energy reached and illuminated the expanding supernova debris.
As the wobble accelerated, the observed fluctuations in brightness arrived closer together, producing the chirp.
The researchers considered several other explanations. Farah said they “tested several ideas, including purely Newtonian effects and precession driven by the magnetar’s magnetic fields, but only Lense-Thirring precession matched the timing perfectly.”
More precisely, among the mechanisms tested, only Lense–Thirring precession reproduced both the approximate period of the fluctuations and the rate at which that period shortened. The model did not reproduce every detail of the bumps perfectly, particularly some aspects of their amplitudes, but it successfully connected the chirp’s timing to a physically plausible magnetar.
From that fit came the object’s estimated properties: a rotation period of about 4.2 milliseconds and a magnetic field approximately 300 trillion times stronger than Earth’s.
Why this matters for a 16-year-old theory
Astronomers have long searched for the hidden engines behind superluminous supernovae because ordinary radioactive-supernova models struggle to explain both their brightness and how long they remain luminous. These explosions can shine ten or more times brighter than ordinary supernovae and remain bright for months.
In 2010, Kasen and Lars Bildsten, and separately Stan Woosley, proposed that a rapidly spinning magnetar could supply the additional energy. As the magnetar slowed down, some of its rotational energy would be transferred into the surrounding debris and radiated as light.
The idea remained a leading explanation for about 16 years, but several competing mechanisms could also reproduce the broad shape of a superluminous supernova’s light curve.
SN 2024afav allowed the magnetar theory to be tested against an unusual repeating signal rather than the explosion’s overall brightness alone. The same model independently connected the supernova’s luminosity and the accelerating bumps to consistent estimates of the magnetar’s spin and magnetic field.
Co-author Alex Filippenko called it “definitive evidence for a magnetar forming as the result of a superluminous supernova core collapse.”
Kasen, who was not an author of the study, said: “The chirp in this supernova signal is like that engine pulling back the curtain and revealing that it’s really there.”
Why there is still room for caution
The observations provide unusually strong evidence for a newborn magnetar, but they may not tell the entire story of SN 2024afav.
A separate spectroscopic analysis of the same supernova found evidence that its expanding ejecta were also colliding with material previously expelled by the progenitor star. The researchers detected unusual hydrogen, helium and oxygen features whose appearance coincided with the light-curve bumps.
That circumstellar interaction may therefore have contributed to at least some of the changes in brightness. The Nature team argues, however, that collisions with irregular shells of surrounding material would struggle on their own to produce such smooth fluctuations with a period that shortened so systematically.
The magnetar interpretation is therefore strongly supported, but parts of the event may have had more than one physical cause.
Nor does this single event establish that magnetars power every superluminous supernova. The researchers themselves caution that other explosions may receive much of their energy from collisions between the supernova ejecta and surrounding material.
The chirp provides strong evidence for one magnetar birth, not a universal rule for the entire class.
What astronomers look for next
The discovery gives observers a new signature to hunt for. A sequence of brightness fluctuations that accelerates smoothly over time could point towards another tilted disk precessing around a newborn compact object.
Farah expects astronomers to find dozens more as major surveys such as the Vera C. Rubin Observatory expand their observations of the changing night sky. A larger collection would help reveal how frequently magnetars power superluminous explosions and whether their properties vary from one event to another.