Sun's mood swings not so strange after all, say scientists

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Monday, July 17, 2017

In findings published Friday in Science, a multinational team of scientists led by Antoine Strugarek of the University of Montreal announced the Sun may not be the cosmic oddball amongst solar-type stars some astronomers had believed it to be. They found that, although the Sun's cycles appear to differ from those of other stars of its type, they are governed by the same laws working in the same way.

View of a sunspot, from file.
Image: Atacama Large Millimeter Array.

The Sun has long been known to go through eleven-year cycles of high and low activity, including sunspots, which Strugarek likened to solar volcanoes. Times of high activity are also the most likely time for coronal mass ejections, which often emanate from sunspot regions. On rare occasions these eruptions of plasma may hit the Earth's magnetic field, setting it oscillating. It then releases previously trapped particles as the Aurora Borealis and Australis. Occasionally, the effects are so intense that these charged particles and magnetic effects can ding the performance of satellites and power grids. The poles flip at the time of high activity, and the intensity of the magnetic field peaks when the Sun is least active. A hypothetical heat-proof compass on the surface of the Sun would point toward one pole during one eleven-year period but toward the other during the next.

To predict and explain this activity, Strugarek and colleagues developed a model of the plasma, high-energy matter, inside the sun and examined how its flow and change could create magnetic fields. To build this model, they incorporated data from 27 different stars. .

They found the Sun operated on the same basic principles as other stars: The activity of all stars in the system was found to be driven by their luminosity, their rotation, and nothing else. The luminosity and rotation are used together to determine a star's Rossby number, which is related to plasma flow. The smaller the Rossby number, the less active the star with respect to magnetic reversals.


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