For the first time, astronomers have witnessed the birth of one of them the universe’s most powerful magnetsor magnetars, at the heart of an unusually bright supernova, thanks to an effect first predicted by Albert Einstein.
According to the researchers, this exciting discovery is the first time general relativity has been needed to describe the mechanics of an exploding star.
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For more than a decade, scientists have predicted that the formation of magnetars could help explain “superluminous supernovae,” which shine at least 10 times brighter than most other stellar explosions. In theory, these rare light shows could occur if a magnetar forms at the supernova’s center, because the supercharged magnetism of the stellar remnant can further accelerate the ejection of charged particles. But until now, no one has been able to prove this.
However, in a new study published on March 11 in the journal Natureastronomers discovered evidence that this phenomenon occurred in a superluminous supernova, called SN 2024afavwhich exploded into the night sky in December 2024.
By analyzing the light curve of SN 2024afav – which shone for more than 200 days and was observed by more than two dozen telescopes around the globe – the team found that after reaching its peak brightness, the explosion did not gradually fade as other supernovae do. Instead, the brightness brightened and dimmed at least four times, which the researchers claim is evidence of a magnetar’s involvement.
“This is definitive evidence that a magnetar forms as a result of a superluminous supernova core collapse,” study co-author Alexei Filippenkoan astronomer at the University of California (UC) Berkeley, said in a statement. It’s also the first time we’ve ever seen a magnetar being born, which is “what’s really exciting,” he added.
In the past, astronomers have witnessed other phenomena such as may have given birth to a magnetarsuch as merger of two smaller neutron stars. However, this new study is the first direct evidence of the birth of a magnetar.
The researchers also estimated the physical properties of the newborn magnetar based on the data they analyzed. They think it probably spins every 4.2 milliseconds (238 times per second) and that its magnetic field is about 300 trillion times greater than Earth’s magnetic fieldwhich shields our planet from potentially dangerous solar storms.
“Strobing Cosmic Lighthouse”
The wobbles in the light curve of SN 2024afav are likely due to an accretion disk surrounding the newborn magnetar. This disk consists of gas and dust from the exploding star that was pulled back towards the stellar remnant by its enormous gravity. This is similar to the disks that are visible around black holes but will almost certainly be asymmetric, meaning it will not be aligned with the magnetar’s spin axis.
Einstein’s general theory of relativity tells us that such a disc will be subject to an effect known as Lense-Thirring precession, which will cause it to wobble relative to the magnetar’s spin axis, causing it to brighten and dim as it passes the line of sight between the remnant star and Earth.
“A wobbly disk can periodically block and reflect light from the magnetar, turning the entire system into a cosmic beacon,” UC Berkeley representatives wrote in the statement.
The researchers discovered four bends in the supernova’s light curve, with each new one shorter and less intense than the previous one. This type of oscillation resembles the cadence of several bird calls, which led the team to call the oscillations “chirping” and is what would be expected from the Lense-Thirring effect.
“We tested several ideas, including pure Newtonian effects and precession driven by the magnetar’s magnetic field, but only Lense-Thirring precession matched the timing perfectly,” study lead author Joseph Farahan incoming research fellow at UC Berkeley and a current doctoral candidate at the Las Cumbres Observatory in California, where SN 2024afav was first discovered, said in the statement. “It is (also) the first time general relativity has been needed to describe the mechanics of a supernova.”
For the researchers who first proposed this idea, the new findings are the “smoking gun” that they were right all along, UC Berkeley representatives wrote.
“For years, the magnetar idea has felt almost like a theorist’s magic trick – hiding a powerful engine behind layers of supernova debris,” Dan Kasenan astrophysicist at UC Berkeley who was one of the first to propose the Lense-Thirring hypothesis but was not involved in the new study, said in the statement. “The chirping of this supernova signal is like the engine that pulls back the curtain and reveals that it’s really there.”
The new findings do not mean that all superluminous supernovae are linked to magnetars, because other researchers have already shown that these bright explosions can also be caused by “cocoons” of gas and dust surrounding exploding stars. But the study team now plans to investigate which of these causes are most common throughout the cosmos.
Using the newly operational Vera C. Rubin Observatory in Chile, which they expect is well suited to detect these wobbly signals.
