Scientists find giant "twists" on the Sun
29 Mar 2009
Scientists have, for the first time, detected giant twisting waves in the lower atmosphere of the Sun, shedding light on the mystery of the Sun's corona. The corona is the region around the Sun, extending more than one million kilometres from its surface, where the temperature is vastly higher than at its surface.
The findings of this investigation, which will help us understand more about the turbulent solar weather and its affect on our planet, has been published today in the journal Science.
The massive solar twists, known as Alfven waves, were discovered in the lower atmosphere with the Swedish Solar Telescope in the Canary Islands by scientists from Queen's University Belfast, the University of Sheffield and California State University Northridge.
< Twisting magnetic fields on the Sun produce bright flares above the solar surface.
The increase in solar temperature from approximately 6,000 degrees Celsius on the visible surface of the Sun (photosphere) to well over a million degrees in the higher overlaying solar corona, has remained at the forefront of astrophysical research for over half a century.
The new observations reveal the process behind this phenomenon, whereby these unique magnetic oscillations spread upward from the solar surface to the Sun's corona with an average speed of over 20 kilometres per second, carrying enough energy to heat the plasma to well over a few million degrees.
"Understanding solar activity and its influence on the Earth's climate is of paramount importance for human kind," said Prof. Mathioudakis, the leader of the Queen's University Belfast Solar Group.
"The Sun is not as 'quiet' as many people think," Prof. Mathioudakis added. "The solar corona, visible from Earth only during a total solar eclipse, is a very dynamic environment which can erupt suddenly, releasing more energy than 10 billion atomic bombs. Our study makes a major advancement in the understanding of how the million-degree corona manages to achieve this feat."
Alfven waves are caused by the twisting of structures in the Sun's atmosphere and can be detected by the periodic velocity signals emitted. The existence of purely magnetic waves in highly magnetised environments was first proposed by Hannes Alfven in 1942, who received a Nobel Prize for his work in this area of research.
A close-up view of the surface of the Sun. >
The Alfven waves detected in this study were found to be associated with a large magnetic field concentration on the surface of the Sun, approximately twice the size of the British Isles. These strong magnetic fields manifest as bright features, often with lifetimes exceeding one hour.
The Swedish Solar Telescope is the largest solar telescope in Europe and produces some of the sharpest images currently available. Bearing in mind that the Sun is 150 million kilometres away, the measurements carried out are equivalent to reading the time on Big Ben in London from Tokyo.
"Often, waves can be visualised by the rippling of water when a stone is dropped into a pond, or by the motions of a guitar string when plucked," said Dr David Jess, from Queen's University Belfast and lead author of the Science paper. "However, Alfven waves cannot be seen so easily. In fact, they are completely invisible to the naked eye."
"Only by examining the motions of structures and their corresponding velocities in the Sun's turbulent atmosphere could we find, for the first time, the presence of these elusive Alfven waves."
Adapted from information issued by STFC.
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