New Ultrasound-like technique finds internal magnetic field in Giant Red Stars

While observing the behaviour of Giant Red Stars, researchers have found that these large celestial bodies boast internal magnetic field which can trap gravity waves inside the star. Newly developed ultrasound-like technique confirmed presence of internal magnetic field that alters the behaviour of giant stars. Magnetic fields play a major while a star goes through evolution phase throughout life — from its birth to death. Now, astrophysicist can determine the inner properties of stars which were previously hidden.

Co-lead author Matteo Cantiello, from University of California Santa Barbara’s Kavli Institute for Theoretical Physics (KITP) said that they used asteroseismology (also known as stellar seismology is the science that studies the internal structure of pulsating stars by the interpretation of their frequency spectra) and tracked the waves entering the stars to determine internal properties of stars.

The idea of determining the internal magnetic field of stars struck Cantiello when astrophysicist Dennis Stello of the University of Sydney presented puzzling data from the NASA’s Kepler telescope that measures stellar brightness variations with very high precision. The striking variations in brightness were only explained when the internal magnetic field was taken into account.

Researchers observed the magnetic field in red giants stars which were several times larger as well as older than our Sun. While examining the phenomenon, researchers found that sound waves due to turbulent motion in the outer regions of the star interacted with the gravity waves moving  towards the stellar core. If the magnetic field is present in the core then it can alter the motions produced the gravity waves.

While explaining, Jim Fuller, a postdoctoral fellow at the California Institute of Technology said that magnetic field affects the movement of gravity waves and if the magnetic field is strong enough, the gravity waves get trapped in the star’s core which is also known as the magnetic greenhouse effect. He further added that trap occurs as gravity waves entering the stellar core gets reflected by the magnetic field at a low degree of symmetry which prevents it from escaping the core. It is similar to when a light enters a diamond and gets trapped as it is reflected at a low angle again and again due to which a diamond sparkles.

The phenomenon results in the smaller amplitudes of stellar surface oscillations when compared to other stars that don’t have strong internal magnetic field. “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 added.

The study appeared in the journal Science.

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