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Calculating the Duration of a Star's Magnetic Cycle


Using new computer simulations, a collaboration involving scientists from IRFU explained why the Sun's magnetic field changes polarity every 11 years. This groundbreaking discovery of a scaling law on the duration of the magnetic cycle of stars will lead to a better understanding of the risks associated with space weather forecasting.
Published on 20 December 2017

The magnetic field of stars is generated by the convective turbulent movements of the conductive fluid within the star (i.e. the dynamo effect). Polarity can change according to regular cycles ranging from one year to several decades. This phenomenon comes with extremely high-energy eruptions which, in the case of the Sun, can have a potentially negative impact on communication systems located on Earth or in orbit.

Using supercomputers (GENCI, PRACE and ComputeCanada), researchers have performed a set of ab initio models and simulations of the magnetism and turbulent flows within Sun-like stars. They provided evidence for strong interdependence between the star's magnetic field and two types of flows: one on a mass scale, and the other, multi-scale. Yet, ultimately, the period of the cycle is determined by the large-scale temporal modulations of the internal rotation of the plasma.

The scaling law determined by the researchers makes it possible to reconstruct the magnetic cycle of the Sun, and of three other solar-type stars. Through various observation programs, astrophysicists have gathered a large amount of data about Sun-like stars (their magnetic cycle, brightness, rotation period, etc.), which, they hope, will help further refine the interpretation of their magnetic cycle.

The scientists will also be able to exploit their new scaling law to better prepare for the scientific exploitation of data from ESA Solar Orbiter's mission Cosmic Vision and PLATO, planned for launch in 2018 and 2024, respectively.

Members of this international collaboration also include CNRS and Université Paris Diderot.

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