Stars stealing from their neighbours: The past that could reveal the secrets of their magnetic field

Some stars may have a hidden past involving stolen material from neighbouring stars. New research suggests that this unusual history could help scientists better understand the magnetic fields found inside stars and improve how they estimate stellar ages

The study, led by researchers at the Institute of Science and Technology Austria (ISTA), was funded by the European Research Council (ERC) and published in Astronomy & Astrophysics. It reveals that a star’s evolutionary history could play a much bigger role in shaping its internal magnetic fields than previously thought.

The mystery of missing stellar signals

Scientists cannot see inside stars directly, but they can study their internal structures by observing tiny changes in their brightness. These changes are caused by vibrations known as stellar oscillations.

This technique, called asteroseismology, works much like how earthquakes help scientists understand Earth’s interior.

Researchers are particularly interested in red giants, Sun-like stars in the later stages of their lives. By studying their oscillations, scientists can investigate what is happening deep inside their cores.

However, some red giants display unusual behaviour known as dipole-mode suppression. This happens when certain oscillation signals become extremely weak or disappear altogether.

Scientists believe strong magnetic fields near the stellar core may be responsible. However, existing models suggest that these magnetic fields would need to be exceptionally powerful, raising questions about how they could have formed.

A case of cosmic theft

One possible explanation is that some stars have gained mass from a neighbouring companion or even merged with another star.

This event could dramatically change the relationship between a star’s core and its outer layers. This altered internal structure could make the star more sensitive to magnetic fields.

As a result, a much weaker magnetic field could produce the same effects on stellar oscillations that scientists previously thought required an extremely strong field.

Testing theory

To investigate this possibility, PhD student Nicolas Muntean and his colleagues used the open-source stellar evolution software MESA to create computer models of stars with and without a history of gaining mass.

The researchers compared how each type of star responded to magnetic fields and discovered a significant difference. Stars that gained mass were far more sensitive to magnetic fields than those that evolved without a companion.

The team also identified red giants already discussed in scientific research whose observed properties could fit this new explanation.

Rethinking how stars evolve

The findings suggest that scientists may need to reconsider how they interpret the magnetic fields inside stars. Assuming that every star evolved independently could lead to inaccurate conclusions about its internal structure.

By accounting for past mergers and mass transfer, researchers could develop more realistic stellar evolution models and improve estimates of stellar ages.

This research highlights how a star’s past may hold the key to understanding its present, showing that even events from billions of years ago can leave lasting clues hidden deep within its interior.