New technique to detect magnetic fields inside stars

Using a technique similar to medical ultrasound, astrophysicists have for the first time developed a way to determine the presence of strong magnetic fields deep inside pulsating giant stars.

Magnetic fields have important consequences in all stages of stellar evolution, from a star's formation to its demise.

The researchers used asteroseismology -- a discipline similar to seismology -- to track waves traveling through stars in order to determine their inner properties.

"We can now probe regions of the star that were previously hidden," said study co-lead author Matteo Cantiello, specialist in stellar astrophysics at University of California Santa Barbara's Kavli Institute for Theoretical Physics (KITP).

"The technique is analogous to a medical ultrasound, which uses sound waves to image otherwise invisible parts of the human body," Cantiello pointed out.

The study analysed data from the Kepler satellite, a space telescope that measures stellar brightness variations with very high precision.

The researchers found that when strong magnetic fields are present in a star's core, the fields can disrupt the propagation of gravity waves, causing some of the waves to lose energy and become trapped within the core.

The researchers coined the term "magnetic greenhouse effect" to describe this phenomenon.

"We used these observations to put a limit on -- or even measure -- the internal magnetic fields for these stars," Cantiello said.

"We found that red giants can possess internal magnetic fields nearly a million times stronger than a typical refrigerator magnet," Cantiello noted.

"This is exciting as internal magnetic fields play an important role both for the evolution of stars and for the properties of their remnants," Cantiello said.

The findings appeared in the journal Science.