KAREN TERAMURA / UNIVERSITY OF HAWAII INSTITUTE FOR ASTRONOMY
The magnetic field of the sunlike star tau Bootis has flipped its north and south poles, the first time this has been observed in a star other than our sun. The shortened cycle of this event might be due to interactions with its nearby massive planet.
UH scientists observe flipping star
A University of Hawaii astronomer and international colleagues caught the star tau Bootis flipping its magnetic field from north to south, similar to the sun's magnetic behavior.
"Now, for the first time, we are probing the magnetic cycles of stars other than the sun," said Evgenya Shkolnik, of the NASA Astrobiology Institute at the University of Hawaii-Manoa Institute for Astronomy.
It is the first time such a change in magnetic field has been seen in a star other than the sun, the researchers said, reporting their work in the British journal Monthly Notices of the Royal Astronomical Society.
What makes tau Bootis so interesting, Shkolnik said in an interview, is that it has a giant planet, about 6.5 times larger than Jupiter, orbiting so closely to it -- only one-twentieth the distance between the sun and Earth.
"It already has successfully managed to lock the star in its own orbit," she said. "It managed to speed up the star so it rotates at the same period as the planet orbit. The same face of the star is always facing the same face as the planet.
"We're guessing that perhaps the interaction with the planet has set up the entire flipping process," Shkolnik added.
The sun's magnetic field reverses about every 11 years, with a minimum to maximum sunspot cycle affecting Earth's climate. The peak activity, called the "solar max," is associated with solar flares, sunspots and solar storms. The sun's last magnetic flip was last year. The new cycle's first sunspot appeared last month, the scientists said. The sun's magnetic cycle also affects Earth's climate.
The team, led by two French astronomers, discovered the magnetic field on tau Bootis in 2006 with the Canada-France-Hawaii Telescope on Mauna Kea and caught the flip in its north and south poles while monitoring it the past year.
Tau Bootis is slightly hotter than the sun and 20 percent larger, the scientists said. It is about 51 light-years away from Earth and bright enough to be visible with the naked eye, near the star Arcturus in the constellation Bootes.
The star's co-rotation with its planet's orbit is the same effect that causes the moon to co-rotate around Earth so only one side of the moon is seen, the scientists said.
With a short rotation period of about three days, the magnetic field will likely flip more often on tau Bootis than it does on the sun, Shkolnik said.
The team's goal is to learn "how magnetic engines work in stars," including Earth's sun. "We're watching every year now to find what exactly the period is and potential effects on the planet itself because magnetic flipping is such an important and interesting phenomenon on the sun," Shkolnik said.