Flip-Flopping Star

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Magnetic activity on the Sun can have a big effect on Earth. Magnetic storms and outbursts can heat the outer atmosphere, create brilliant aurorae, and wreak havoc with power grids and other technology.

But in another star system, a planet may have a big effect on a star's magnetic field -- perhaps causing it to flip over.

The system is Tau Bootis, in Bootes, the herdsman, which is high in the south at nightfall. Tau Bootis is just to the west of the constellation's most prominent star, bright yellow-orange Arcturus.

Tau Bootis is a binary system. Its primary star is a little bigger, heavier, and hotter than the Sun. The star's planet is several times as massive as Jupiter, the giant of our own solar system. It's so close to the star that it orbits once every three-and-a-third days -- which is the same amount of time it takes the star to turn on its axis.

The planet's gravity may be dragging the star along with it. But different parts of the star rotate at different speeds, just as the Sun does. That generates a magnetic field.

Last year, a team led by Andrew Cameron of Saint Andrews University in Scotland found that the star's magnetic field had flipped over since the year before. The Sun's magnetic field flips, too, every 11 years. But Tau Bootis's field flipped much quicker than the Sun's does. It's possible that the nearby planet speeds up its magnetic cycle, causing Tau Bootis to flip-flop every few years.

Script by Damond Benningfield, Copyright 2008

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