New investigations of a tiny star in the constellation of Pegasus have provided a novel insight into the Sun and its potential impact on Earth.

An international team of astronomers, including scientists from the University of St Andrews, have developed a new understanding of how stars, including the Sun, generate their magnetic fields. The new finding may help develop further understanding of how changes in the magnetic field of the Sun impact on Earth's climate.

The researchers from France and Scotland made a crucial discovery when studying a small cool star 20 light-years from the Sun. The researchers used new methods to make the first magnetic map of the star, and found that this star has a very simple magnetic field, much like that of the Earth's.

They explained: "Studying magnetic fields of stars is a novel way of studying the magnetic field of our Sun. Although it always looks the same, the Sun is variable, and the changes in its magnetic field, although small, appear to affect the Earth's climate. Scientists think that a well-documented decrease in the Sun's magnetic activity is the most probable cause of the Little Ice Age, the cool period that prevailed on Earth from the 15th to the 18th century."

The star, named V374 Pegasi, lies about 20 light-years from the Sun, in the constellation of Pegasus. Although it is one of the Sun's closest stellar neighbours -- much nearer to us than most of the stars visible in the night sky -- V374 Peg is more than 100 times too faint to see with the unaided eye. It is an ultra-cool star, one-third of the size of the Sun, with a surface temperature of only 2900 C, in contrast to the Sun's 5500 C.

The researchers examined the magnetic field of the star using the most powerful instrument worldwide for carrying out this kind of research, currently attached to a telescope in Hawaii. The new instrument was especially designed by the Observatoire Midi-Pyrenees in France for observing and studying magnetic fields in stars other than the Sun, and is the only instrument that can study magnetic field topologies of small, faint stars such as V374 Peg, that are notoriously difficult to observe in detail.

The researchers were surprised to discover that the star had a simple form of magnetic field.

"Scientists had previously predicted that magnetic fields of such small, cool stars should be more chaotic and less structured than those seen in the Sun. The new observations show instead that the ultra-cool star V374 Pegasi has a very simple, organised global magnetic field structure rather like that of the Earth. It came as a complete surprise to us," they explained.

Further investigations on similar stars may reveal more clues about the Sun itself and its likely impact on Earth.

They said: "These changes of the Sun are attributed to long-term changes of the magnetic field that the Sun produces in its interior, through a mechanism which is not yet fully understood. But it's like trying to understand a disease with only one patient. By studying the magnetic diseases of other stars, we should develop new insights into the Sun's behaviour."

The results are published in the 3 February 2006 issue of Science.

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