Unusual supernova signal could reveal what powers the universe’s brightest explosions
About a billion light years away, an extraordinary stellar explosion lit up the night sky. The explosion, detected on December 12, 2024was about 30 times greater than the luminosity of a typical supernova, placing it in a rare group of superluminous supernovas. Today, astronomers think they know what made the explosion so bright… an extreme type of star called a magnetarreports the team on March 11 in Nature.
“Superluminous supernovae are 10 to 100 times brighter than ordinary supernovae,” explains 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.” It’s not a sound we can hear, but rather a signal that astronomers can see. Chirping is a fluctuation in brightness that increases in frequency over time, meaning that the light from the supernova brightens and dims in increasingly rapid cycles.
“No supernova has chirped before, so there must be something weird going on,” says Farah.
He was part of a team that studied the supernova with a global network of telescopes called Las Cumbres Observatory. The team then performed computer simulations of the light from the explosion. The results suggest that the supernova’s extreme light show was driven by a dense, highly magnetized object called a magnetar. When a star’s core collapses and triggers a supernova, it usually leaves behind a black hole or dense neutron star. Magnetars are neutron stars with extreme magnetic fields.
Farah says a magnetar is the only solid explanation for the 2024 supernova chirp, supporting previous ideas that rotating magnetars can power these superluminous events.
“Seeing something completely new, and then making a prediction as it happens, and then that prediction comes true, it’s like you’ve just had a conversation with the universe,” he says.
Finding additional superluminous supernovas with a chirpy signal would help confirm the team’s findings.
“I don’t think it’s smoking gun yet,” says astrophysicist Matt Nicholl of Queen’s University in Belfast, Northern Ireland. “It’s very difficult to explain a chirp in any other way. It’s just a matter of confirming that we actually see a chirp,” he says. “It’s certainly the most convincing one out there, but I’d just like to see a few more before I declare this to be evidence of the magnetar.”
If a magnetar was indeed causing the 2024 event, scientists would still have to explain exactly how. Farah and his colleagues suggest that 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 oscillation accelerated, it could have produced the warble of the supernova’s light signal.
“The best way to imagine it is if you were an observer trying to sit around the magnetar, it would be really, really difficult because your spacetime is literally being trained to co-rotate with the magnetar,” says Farah. This effect is stronger the closer you get to the magnetar, which causes the disk to oscillate.
Astronomers may soon have more opportunities to study these huge explosions. A new telescope in Chile called the Vera C. Rubin Observatory is expected to discover thousands of new superluminous supernovas. So far, only about 300 have been discovered.
If future stellar explosions contain chirps and scientists confirm that the cause is a magnetar’s wobbly disk, Farah says, “it would give us new ways to test general relativity and our theories of fundamental physics.”
