Australasian Science: Australia's authority on science since 1938

Nearby Star Offers New Insight into Earth’s Sun

After nearly a decade of intensive searching, an international team of astronomers has discovered the first star that varies its magnetic field like our own Sun.

The “BCool Project”, an international collaboration studying the dynamo generation of magnetic fields in cool stars, has been mapping the magnetic fields of a number of nearby stars using the Bernard Lyot Telescope in the French Pyrenees.

The observations included the star 61 Cyg A, one of the Sun’s nearest neighbours just over 11 light years away. Unlike the Sun, 61 Cygni is a binary star, with its two components – 61 Cyg A and 61 Cyg B – both somewhat smaller and dimmer than the Sun.

“The Sun’s activity is intrinsically tied to its magnetic field,” explained Dr Stephen Marsden of the University of Southern Queensland, who co-authored the research report published in Astronomy & Astrophysics. “It drives the Sun’s spots, flares, and fuels the Solar wind – a torrent of material that streams off our star into space,” he said.

“We have known for many years that most, if not all, stars are variable to some degree, with this variability, or activity, being caused by the star’s magnetic field. The Sun, our closest star, is no exception, varying through the course of a roughly 22-year-long magnetic cycle, with it ‘flipping’ the polarity of its magnetic field every 11 years.

“The Sun’s variations are relatively small and very slow – a stark contrast to the great bulk of known variable stars, who vary dramatically in brightness, release enormous, violent stellar flares, or oscillate with periods of just a few days or months.”

Marsden said astronomers have observed nearby stars for behaviour similar to our Sun and noted similarities, but it had been unknown if this variability coincided with a “flipping” magnetic field like that of our own Sun.

BCool’s observations revealed that 61 Cyg A is very similar to the Sun. A little dimmer and a little cooler, the star nevertheless exhibits changes in its activity coinciding with polarity changes in its magnetic field every 7 years during its 14-year magnetic cycle. 61 Cyg A also shows an increased complexity in its magnetic field as it approaches these “flips”.