A Strange Signal in a Supernova Finally Confirms a 16-Year-Old Theory

Astronomers have found the first clear proof that a magnetar forms during a superluminous supernova. This discovery helps us understand some of the universe's brightest explosions.

A magnetar is a neutron star that spins very fast and has an incredibly strong magnetic field. This finding confirms a theory from 16 years ago and shows a new way stars explode. Some supernovae show a "chirp" pattern in their light, which is explained by general relativity. This research was published in the journal Nature.

The Mystery of Superluminous Supernovae

Superluminous supernovae can be more than 10 times brighter than typical stellar explosions. Since they were first seen in the early 2000s, scientists have been puzzled by them. Experts thought these explosions came from the deaths of very massive stars, perhaps 25 times the size of our sun. However, their brightness lasts much longer than expected after a star's core collapses.

In 2010, Dan Kasen, a theoretical astrophysicist at UC Berkeley, suggested that a newly formed magnetar could power this long-lasting glow. His idea, also proposed by Lars Bildsten and Stanford Woosley, explains what happens when a massive star dies.

When a massive star collapses, much of its material squeezes into a super-dense neutron star. This is almost a black hole. If the original star had a strong magnetic field, the collapse could make it much stronger, forming a magnetar. This magnetar would have a magnetic field 100 to 1,000 times stronger than regular spinning neutron stars called pulsars.

Both pulsars and magnetars are only about 10 miles (16 kilometers) wide. Young ones can spin over 1,000 times per second. As a magnetar spins, its strong magnetic field speeds up charged particles. These particles hit the debris from the supernova, adding energy and making the explosion brighter. Magnetars are also thought to be a source of fast radio bursts.

A New Supernova Reveals its Engine

Joseph Farah, a graduate student, studied observations from a supernova called SN 2024afav, discovered in 2024. Farah will join Kasen's research group at UC Berkeley.

Farah confirmed the link between magnetars and Type I superluminous supernovae (SLSNe-I). In the Nature paper, he and his team suggested that unusual bumps in the supernova's light curve are due to general relativity. They call this repeating pattern a "chirp." Their analysis shows it points directly to a magnetar at the center of the explosion.

Alex Filippenko, a UC Berkeley professor and co-author, said this is clear proof that a magnetar forms from a superluminous supernova core collapse. He noted that Kasen and Woosley's model suggested the magnetar's energy deep inside would explain the extreme brightness. Farah's paper shows that a magnetar actually forms there.

Kasen added that the magnetar idea felt like a "magic trick" for years, hiding a powerful engine. He said the "chirp" in this supernova signal is like the engine pulling back the curtain to show it's real.

The Distant Discovery

After SN 2024afav was found in December 2024, the Las Cumbres Observatory, a network of 27 telescopes, tracked it for over 200 days. The exploding star was about a billion light-years away.

Farah noticed that after the supernova's brightness peaked around 50 days, it didn't just fade. Instead, its brightness slowly wobbled downward, with the wobbles getting faster. This created a series of four bumps, like a bird's chirp.

Other superluminous supernovae had shown a couple of bumps, which some thought were from the supernova shock hitting gas around the star. But no one had seen four bumps before.

A Relativistic "Chirp"

Farah's model suggests that some material from the SN 2024afav explosion fell back toward the magnetar, forming an accretion disk. Because the material around the magnetar isn't perfectly even, the accretion disk wouldn't be perfectly aligned with the magnetar's spin.

General relativity says that a spinning mass drags space-time with it. This effect, called Lense-Thirring precession, would make the misaligned disk wobble. A wobbling disk could block and reflect light from the magnetar, making the system flash like a cosmic lighthouse. As the disk moves closer to the magnetar, it wobbles faster, causing the light to oscillate more rapidly as it fades. This creates the "chirp" seen from Earth.

Farah said they tested several ideas, but only Lense-Thirring precession matched the timing perfectly. He noted it's the first time general relativity has been needed to describe a supernova's mechanics.

Astronomers also used the data to estimate the neutron star's spin period: 4.2 milliseconds. Its magnetic field was about 300 trillion times that of Earth. Both are signs of a magnetar.

Andy Howell, a senior scientist at LCO, called Farah's finding the "smoking gun." He said it ties the bumps to the magnetar model and explains everything with general relativity, calling it "incredibly elegant." Filippenko added that seeing a clear effect of Einstein's general theory of relativity in a supernova is especially rewarding.

Filippenko cautioned that this doesn't mean all superluminous supernovae are powered by magnetars. Another theory suggests the shock wave from the explosion hitting surrounding material can also increase brightness. Kasen also proposed that if a star's core collapse forms a black hole with a misaligned accretion disk, it could also power a brighter supernova and create bumps in the light curve.

Filippenko believes this discovery accounts for some Type I superluminous supernovae, meaning fewer are likely powered by surrounding material than previously thought.

Future Searches for "Chirping" Supernovae

Farah expects to find many more "chirping" supernovae when the Vera C. Rubin Observatory starts its comprehensive sky survey.

Farah called this the most exciting thing he's been part of, saying it's the universe challenging us to understand it better.

Deep Dive & References

Lense–Thirring precessing magnetar engine drives a superluminous supernova - Nature, 2026