Starquakes reveal massive internal magnetic fields

January 27, 2016 - 08:45

Astrophysicists studying starquakes have discovered powerful magnetic fields within red giants, which can tell us a lot about how the stars were born, lived, and died.

A star's inner magnetic field can change the way waves propagate through it. (Illustration: RA García, K. Augustson, J. Fuller, G. Pérez / AIA / SDO)

Stars do more than just shine. They also vibrate, which makes them swing in all directions.

Using NASA's Kepler space telescope, it’s possible to measure these changes, which helps astrophysicists to unlock the inner workings of these stars.

A team of scientists recently used the method known as asteroseismology to analyse 3,600 red giants and they discovered powerful magnetic fields in the interior of some of these stars.

"We believe we’ve found a method to measure the magnetic field hidden within a star’s interior,” says co-author Victor Silva Aguirre, adjunct professor at Aarhus University, Denmark.

“We can only see the surface of the star, so it’s not easy, but we can model the magnetic fields by studying variations in their brightness," says Aguirre.

The new results are published in the scientific journal Nature.

Strong waves travel to the star’s core

Aguirre and colleagues measured strong seismic waves that started in the outer layer of the stars, and travelled towards the star’s core.

“The waves are reflected back to the surface when they hit the core, but not always,” says Aguirre.

“We believe, based on theoretical models that a lack of reflection of these waves in some of the stars must be due to strong magnetic fields at their core," he says.

The sun will become a red giant

A star is born when a large cloud of dust and gas collapses under its own gravity. Astrophysicists expect that their magnetic field also form at this time.

We are familiar with the variable magnetic field of our own star, the sun, whose magnetic poles switch every 11 years. But we do not know much about how other stars behave.
Now it seems that at least half of the red giant stars that weigh between 1.6 and 2 times as much as the sun, are hiding strong magnetic fields in their interior.

These red giant stars have already consumed the hydrogen at their heart and now the core processes continue within a shell that surrounds the core as the star grows dramatically and takes on a red colour. Our own Sun will become a red giant in time.

But small stars--smaller than the sun--do not seem to retain a strong magnetic field at their core when they evolve into red giants. This is probably because it was not there to begin with.

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Read the Danish version of this story on Videnskab.dk
 

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Translated by
Catherine Jex