Strong magnetic fields discovered in majority of stars: study

 
STRONG magnetic fields have been discovered in the majority of stars — a breakthrough finding set to impact research into their evolution.

An international group of astronomers, led by the University of Sydney, found that stars only slightly bigger than the sun have internal magnetic fields (or moving electric charges) up to 10 million times that of the Earth.
“This is tremendously exciting, and totally unexpected. Because only five to 10 per cent of stars were previously thought to host strong magnetic fields, current models of how stars evolve lack magnetic fields as a fundamental ingredient,” lead researcher Associate Professor Dennis Stello, a University of Sydney astrophysicist, said.
“Such fields have simply been regarded insignificant for our general understanding of stellar evolution. Our result clearly shows this assumption needs to be revisited.”

Strong magnetic fields ... stars like the sun become red giants towards the end of their lives. The red giants of the same mass as the sun do not show strong magnetic fields in their interior, but for stars slightly more massive, up to 60 per cent host strong magnetic fields. Picture: Nature/University of SydneySource:Supplied

The research, which uses data from NASA’s Kepler mission, is based on earlier studies which found that measurements of sound waves (stellar oscillations) inside stars could be used to infer the presence of strong magnetic fields.
In the latest study, researchers looked at a large number of “evolved versions” of the sun (or “red giants”), 700 of which displayed strong magnetic fields.
“Because our sample is so big 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,” Associate Professor Stello said.
“In the past we could only measure what happens on the surfaces of stars, with the results interpreted as showing magnetic fields were rare.”

Core convection ... the magnetic fields seen in red giants are left over from an earlier phase when the stellar cores hosted turbulent convection, creating a ‘magnetic dynamo’. Picture: Nature/University of SydneySource:Supplied

Astronomers can now see very strong magnetic fields near a star’s core. This is important because magnetic fields can change what happens inside the core which shapes a star’s ageing process.
“Their interior is essentially ringing like a bell,” Associate Professor Stello said.
“And like a bell, or a musical instrument, the sound they produce can reveal their physical properties.”
He said the findings will help scientists directly test theories of how magnetic fields form and evolve inside stars, potentially leading to a better understanding of communication systems and cloud cover on Earth.

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