COURTESY DAVID AGUILAR, CFA
An artist's view of the giant exoplanet orbiting Tau Bootis, through the star's magnetic arcs. Astronomers using the Canada-France-Hawaii Telescope on Mauna Kea for the first time have directly measured magnetism on a star.
Magnetic field detected on star
The Mauna Kea find is the first for a star that is not the sun
Astronomers using the Canada-France-Hawaii Telescope on Mauna Kea for the first time have directly measured magnetism on a star.
The magnetic field on Tau Bootis, 50 light-years away, is 100 times weaker than a typical refrigerator magnet, said Evgenya Shkolnik, astronomer with the NASA Astrobiology Institute at the Institute for Astronomy.
"Isn't that incredible?" she said, attributing the discovery to the extreme sensitivity of the instrument the scientists are using on the telescope.
They used a high-resolution spectropolarimeter developed by the French for the CFH Telescope.
Their discovery -- the first of a magnetic field on a star that is not the sun -- is published in a Letter to the journal Monthly Notices of Royal Astronomical Society.
"We've known stars have magnetic fields through indirect ways," Shkolnik said. "This is the first time it was directly from starlight."
The Earth's magnetic field, by comparison, is 200 times weaker than a refrigerator magnet, Shkolnik noted. "It makes sense. If the Earth's magnetic field was much stronger, magnets would be flying off the fridge and heading for the North Pole," she laughed.
Tau Bootis is similar to the sun, but is orbited every three days by a giant extrasolar planet more than 1,000 times larger than Earth, Shkolnik said.
She said the star's magnetic field "is tied up in knots," possibly because of the giant planet's influence.
It's known as a "hot Jupiter system" because the planet is about the mass of Jupiter and the star is hot, with temperatures about 2,000 degrees, because they're so close, she said.
In work in Canada, Shkolnik said she and her colleagues discovered indirect evidence of magnetic heating of two different stars that had hot Jupiters orbiting. "This is the first time we had ever seen a planet affect a star."
It's "kind of a celestial role reversal," she said, with the planet influencing the star rather than the opposite. "This is a paradigm shift in a lot of ways. In our solar system, planets are so far away from the sun and the ones close in are small and don't affect the sun in an observable way."
The Tau Bootis-planet system is the only one known where the planet and star are tidally locked so that one side of the star always sees the same side of the planet, Shkolnik said.
The star and planet both make one rotation and one orbit in about three days. But the star's equator is rotating about 20 percent faster than its pole, the scientists reported.
Shkolnik said using the CFH telescope, she said, "We decided to look to see, can the planet influence the star? And it is. It appears to be magnetically interacting with the star."
The group was awarded time on the telescope in July to continue studying Tau Bootis and a set of similar stars that have hot Jupiters, Shkolnik said.
They're going to try to map the star's magnetic geometry to try to learn more about how the planet is interacting with the star and affecting it, she said.