Once believed to be rare, strong magnetic fields actually exist around the majority of stars, an international team of astronomers revealed in Monday’s edition of the journal Nature—and their discovery could radically alter our understanding of how stars evolve.

The researchers, led by astrophysicist Dennis Stello of the University of Sydney, reviewed data from NASA’s Kepler mission and found that stars only slightly more massive than our own sun have internal magnetic fields as much as 10 million times stronger than the Earth’s.

“This is tremendously exciting, and totally unexpected,” Stello, an associate professor, said in a statement. “Because only 50 percent of stars were previously thought to host strong magnetic fields, current models of how stars evolve lack magnetic fields as a fundamental ingredient. Such fields simply been regarded insignificant for our general understanding of stellar evolution.”

The new findings, which build upon previous research led by experts at the Californian Institute of Technology (Caltech) that found that sound waves within stars could be used to detect strong magnetic fields, “clearly shows this assumption needs to be revisited,” Stello added.

One-fifth of stars found to possess strong magnetic fields

The researchers looked at measurements of these sound waves, also known as stellar oscillations, in 3,600 red giant stars, which are stars with roughly the same mass as the sun but are in the final stages of their lives. They discovered that 20 percent of these stars (more than 700) showed signs of having strong magnetic fields that suppressed some of those oscillations.

“Because our sample is so big,” Stello said, “we have been able to dig deeper into the analysis and can conclude that strong magnetic fields are very common among stars that have masses of about 1.5-2.0 times that of the Sun. In the past we could only measure what happens on the surfaces of stars, with the results interpreted as showing magnetic fields were rare.”

He and his colleagues used a technique known as asteroseismology, which allowed them to look beneath the surface of a star and find whether or not it possessed a strong magnetic field near its core. These magnetic fields can alter the physical processes that take place in the stellar core, the study authors explained, including internal rotation rates that determine how the stars age.

Most stars have sound waves that bounce back and forth, essentially ringing like a bell on their interior, Stello said. The resulting sound can be used to reveal their physical properties, and the researchers measured slight variations in brightness caused by this so-called ringing. They found that magnetic fields suppressed specific oscillation frequencies in 60 percent of the stars.

As a result, they will now be able to directly test theories of how these magnetic fields form and evolve inside stars, and their work could shed new light on the processes that control the 22-year magnetic cycle of the sun. Stello and his colleagues now plan to find out just why these magnetic fields are more common than originally expected.

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Feature Image: University of Sydney

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