Simulation of the interior of a solar-type star.
Credit: University of Montréal – DAp/CEA – AIM
The Sun is a solar-type star, a new study claims — resolving an ongoing controversy about whether the star at the center of our Solar System exhibits the same cyclic behavior as other nearby, solar-type stars. The results also advance scientists’ understanding of how stars generate their magnetic fields.
The Sun’s activity — including changes in the number of sunspots, levels of radiation and ejection of material – varies on an eleven-year cycle, driven by changes in its magnetic field. Understanding this cycle is one of the biggest outstanding problems in solar physics, in part because it does not appear to match magnetic cycles observed on other solar-type stars — leading some to suggest the Sun is fundamentally different.
Here, by carrying out a series of simulations of stellar magnetic fields, Antoine Strugarek and colleagues show that the Sun’s magnetic cycle depends on its rotation rate and luminosity. This relationship can be expressed in terms of the so-called Rossby number; they show that the magnetic cycle of the Sun is inversely proportional to this number. Comparing the results of their simulations with available observations of cyclic activity in a sample of nearby solar-type stars, the authors further find that the cycle periods of the Sun and other solar-type stars all follow the same relationship with the Rossby number.
The results demonstrate that the Sun is indeed a solar-type star.
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J.-D. do Nascimento Jr et al. Reconciling solar and stellar magnetic cycles with nonlinear dynamo simulations. Science,July 2017 DOI:10.1126/science.aal3999