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Tags Current Affairs

Slowdown in Sun’s activity

Date: 03 May 2020 Tags: Space

Issue

 For the first time, the scientists compared the sun with hundreds of other stars with similar rotation periods. Most displayed much stronger variations. This raises the question whether the sun has been going through an unusually quiet phase for several millennia.

    

Background

The extent to which solar activity (and thus the number of sunspots and the solar brightness) varies can be reconstructed using various methods, at least for a certain period of time.

 

Details

  • Since 1610, there have been reliable records of sunspots covering the Sun; the distribution of radioactive varieties of carbon and beryllium in tree rings and ice cores allows us to draw conclusions about the level of solar activity over the past 9000 years.

  • Since there is no way of finding out how active the Sun was in primeval times, scientists can only resort to the stars. Researchers investigated, whether the Sun behaves "normally" in comparison to other stars. This may help to classify its current activity.

  • The researchers selected candidate stars that resemble the Sun in decisive properties. In addition to the surface temperature, the age, and the proportion of elements heavier than hydrogen and helium, the researchers looked above all at the rotation period.

  • A star's rotation contributes to the creation of its magnetic field in a dynamo process in its interior. The magnetic field is the driving force responsible for all fluctuations in activity.

  • The state of the magnetic field determines how often the Sun emits energetic radiation and hurls particles at high speeds into space in violent eruptions, how numerous dark sunspots and bright regions on its surface are, and thus also how brightly the Sun shines.

  • The researchers scoured this huge sample and selected those stars that rotate once around their own axis within 20 to 30 days. The researchers were able to further narrow down this sample by using data from the European Gaia Space Telescope.

  • The exact analysis of the brightness variations of these stars from 2009 to 2013 reveals a clear picture. While between active and inactive phases solar irradiance fluctuated on average by just 0.07 percent, the other stars showed much larger variation.

  • The researchers also studied more than 2500 Sun-like stars with unknown rotation periods. Their brightness fluctuated much less than that of the other group.

  • These results allow two interpretations. There could be a still unexplained fundamental difference between stars with known and unknown rotation period. 

  • For the last decade, the Sun has been showing itself to be rather weakly active, even by its own low standards. Predictions of activity for the next eleven years indicate that this will not change soon.

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