A strange ‘chirp’ in a brilliant stellar blast points to a magnetar
The unusual supernova signal may reveal what powers the universe’s brightest blasts
An extreme star called a magnetar, surrounded by a wobbling accretion disk (illustrated), may have created a never-before-seen signal recently detected by astronomers.
Joseph Farah and Curtis McCully
About a billion light-years away, an extraordinary stellar explosion lit up in the night sky. The blast, detected December 12, 2024, was some 30 times the brightness of a typical supernova, putting it in a rare group of superluminous supernovas. Now, astronomers believe they know what made the explosion so bright — an extreme type of star called a magnetar, the team reports March 11 in Nature.
“Superluminous supernovae are 10 to 100 times brighter than regular supernovae,” says astrophysicist Joseph Farah of the University of California, Santa Barbara.
What makes the new superluminous supernova unique is that it appears to contain a distinct signal that scientists call a “chirp.” This is not a sound we can hear, but instead a signal astronomers can see. The chirp is a brightness fluctuation whose frequency increases over time, meaning the supernova’s light brightens and dims in cycles that come faster and faster.
“No supernova has had a chirp before, so there has to be something weird going on,” Farah says.
He was part of a team that studied the supernova with a global network of telescopes called the Las Cumbres Observatory. The team then ran computer simulations of the explosion’s light. The results suggested the supernova’s extreme light show was driven by a dense, highly magnetized object called a magnetar. When the core of a star collapses and triggers a supernova, it usually leaves behind a black hole or a dense neutron star. Magnetars are neutron stars with extreme magnetic fields.
Farah says a magnetar is the only strong explanation for the chirp in the 2024 supernova, supporting prior ideas that rotating magnetars can power these superluminous events.
“To see something brand new, and then to make a prediction as it’s happening, and then that prediction comes true — it’s like you just had a conversation with the universe,” he says.
Finding additional superluminous supernovas with a chirp signal would help confirm the team’s findings.
“I don’t think it’s the final smoking gun yet,” says astrophysicist Matt Nicholl of Queen’s University Belfast in Northern Ireland. “It’s very hard to explain a chirp any other way. It’s really just about confirming we are definitely seeing a chirp,” he says. “This is certainly the most convincing one that’s out there, but I just would like to see a few more before I declare it is indeed proof of the magnetar.”
If a magnetar did drive the 2024 event, scientists would still need to explain exactly how. Farah and colleagues suggest a disk of gas and dust from the exploded star formed around the magnetar during the supernova. This disk would have wobbled due to extreme gravitational effects, blocking or redirecting varying amounts of light at different times. As the wobbling sped up, it could have produced the chirp in the supernova’s light signal.
“The best way to imagine it is, if you were an observer trying to sit still around the magnetar, it would be really, really hard because your spacetime is literally being dragged to corotate with the magnetar,” Farah says. This effect is stronger the closer you are to the magnetar, which is what causes the disk to wobble.
Astronomers may get more opportunities to study these immense explosions soon. A new telescope in Chile called the Vera C. Rubin Observatory is expected to discover thousands of new superluminous supernovas. Only about 300 have been discovered so far.
If future stellar explosions contain chirps, and if scientists confirm the cause is a magnetar’s wobbling disk, Farah says, “that would give us new ways to test general relativity and our theories of fundamental physics.”
