This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Magnetic fields exist in many stars, including the sun. Yet they remain too poorly understood to be reliably included in stellar evolution models, limiting their accuracy.
Now, a new study by researchers at the Institute of Science and Technology Austria (ISTA), published in Astronomy & Astrophysics, shows why a star's "criminal" evolutionary history may be crucial for correctly interpreting its internal magnetic fields. To determine stellar ages, researchers use theoretical stellar evolution models that need to be as accurate as possible—and that means also taking magnetic fields into account. Yet it is often unclear how strong these fields are, where exactly they are located or how they are shaped.
Their complex geometry is difficult to determine with the available data. A new study by assistant professor Lisa Bugnet's research group at the Institute of Science and Technology Austria (ISTA), in collaboration with the Universidad de La Laguna in Tenerife and Université Paris Cité, now shows that, in some old suns, signals may point to a "criminal" past in which they may have "stolen" mass from a companion star. Such an event would reshape the relationship between the star's core and envelope structure, leaving it far more susceptible to the effects of magnetic fields compared with a "normal" single star.
We can't look directly inside stars: They are too far away and opaque. But researchers can use highly precise telescopes to measure tiny, regular changes in their brightness. These changes are caused by vibrations or oscillations.
Every star has its own pattern of oscillations, depending on its internal structure. This branch of astrophysics is called asteroseismology. It is like seismology on Earth: While seismic waves reveal information about our planet's interior, stellar oscillations give researchers insights into the interior of stars.
Of particular interest to Nicolas Muntean, a Ph.D. student in the Bugnet group, are red giants—sunlike stars in a late phase of their lives—and so-called dipole mixed modes. The latter are oscillations that probe regions close to the stellar core. In some red giants, these dipole mixed modes are barely visible.
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