Solar flares cause 'starquakes' on the sun

AARHUS, Denmark, April 22 (UPI) -- Danish physicists say data from the observatory spacecraft SOHO shows powerful "starquakes" occur on the sun in the wake of strong solar flares.

The Solar and Heliospheric Observatory, or SOHO -- a joint venture of the European Space Agency and the National Atmospheric and Space Administration -- was used to study the phenomenon referred to as starquakes. Scientists said a class of oscillations called the 5-minute oscillations, with a frequency of around 3 millihertz, have proven particularly interesting.

The scientists said the 5-minute oscillations can be thought of as the sound produced by a bell in the middle of the desert, constantly being touched by wind-blown random sand grains. But Christoffer Karoff and Hans Kjeldsen, of Denmark's University of Aarhus, discovered something different.

"The signal we saw was like someone occasionally walking up to the bell and striking it, which told us that there was something missing from our understanding of how the sun works," Karoff said.

The cause, they discovered, was solar flares. When the number of solar flares increased, so did the strength of the 5-minute oscillations.

The study is to appear in the May 1 issue of the Astrophysical Journal Letters.