Wednesday, February 13, 2008

Solar magnetic shift, a nearby star, celestial mayhem

Our sun switches magnetic poles every 11 years, to the accompaniment of a great deal of celestial mayhem that astronomers casually call the solar maximum.

(Image: The star tau Bootis is shown with its gas giant in close orbit, in this image by Karen Teramura of the University of Hawai'i Institute for Astronomy.)

Now, another star has been observed doing the same thing. The star is tau Bootis, which passes directly over Hawai'i and lies next to the navigational star Hokule'a or Arcturus, in the constellation Bootes. The star is about 51 light years away.

(By contrast, the North Star, Polaris, is 430 light years away, and the brightest star in our heavens, Sirius, is just 8.7 light years away--a light year being the distance in which something traveling at the speed of light goes in a year.)

The tau Bootis finding was made by University of Hawai'i astronomer Evgenya Shkolnik and an international team that included pair of French astronomers, Jean-Francois Donati, Claire Moutou, Rim Fares and Magali Deleuil, Moira Jardine and Andrew Collier Cameron of the United Kingdom and David Bohlender and Gordon Walker of Canada.

They used the Canada-France-Hawai'i telescope atop Mauna Kea on Hawai'i Island. Their work was published this week in the journal “Monthly Notices of the Royal Astronomical Society.”

The observation is important because it may provide insight into the magnetic shifts of our own sun. Those shifts can cause severe disruptions in communications, in the Earth's own magnetic field and may have other impacts, like the amount of ozone produced in the upper atmosphere and changes in wind patterns.

Scientists believe that an unusual period of low solar activity in the late 1600s and early 1700s may have been responsible for the 17th Century's Little Ice Age.

Shkolnik said tau Bootis may switch magnetic poles much more frequently than our sun does. And that may be caused by the presence of a massive, gas giant planet that whips around the star at amazing speed.

“The increased gravitational energy may have sped up its magnetic cycles,” Shkolnik said.

Tau Bootis is roughly the size of our own sun. But its planet is six times the size of Jupiter, and is in a very tight orbit—just one-twentieth the distance of the Earth to our sun, and an eighth of the distance of Mercury to the sun.

The big planet orbits its sun in just 3.3 days. The massive gravity of the spinning planet has speeded up the star's rotation, so that it spins in 3.3 days, and the same side constantly faces the planet, Shkolnik said. It's the same effect that causes the same side of the moon to constantly face Earth.

The astronomers had just been watching the star for two years when they detected the flipping of the magnetic field from north to south during the past year. They were in the process of mapping the magnetic field of stars. It was the first time such a magnetic change has been seen in another star. They're now watching to see when the next switch takes place.

In our solar system, the magnetic field switches poles on a schedule of every 11 years. While it is in the process of making the shift, the sun releases dramatic amounts of energy and has a peak in sunspot activity. The last such magnetic switch occurred in 2007.

The Earth switches magnetic poles too, but on a much longer time scale. And the Earth's geomagnetic shifts are far more irregular.

An article on the American Geophysical Union website,, suggests that the planet's magnetic field is weakening and could reverse within 2,000 years.

See more on the tau Bootis reversal on the web at

© 2007 Jan W. TenBruggencate