segunda-feira, 25 de fevereiro de 2008

Star Flips its Magnetic Field

by Fraser Cain

At some point in the last year or so, the Sun-like star tau Bootis completely flipped its magnetic field. The star's north pole became its south pole, and vice versa. It this going to happen to our own Sun? Yes! Don't panic though; in fact, it happens every 11 years or so.Even thought the Sun's magnetic field flip has been well observed, astronomers have never seen this happen on another star. With the Sun, the field reversals are closely linked to varying number of sunspots on its surface. The magnetic field flip happened last time in 2007, when the Sun was at the "solar minimum".

The Earth has been recorded to change its magnetic field too, but this event has happened very erratically in the past, and theres no way to predict when it's going to happen again in the future.
And international team of astronomers were watching the star tau Bootis with the Canada-France-Hawaii Telescope Mauna Kea as part of a survey measuring the magnetic field of stars. On one sweep the star had one configuration, and later on, the magnetic field was reversed.

Since this event happened within just two years of observations, it's likely that tau Bootis flips its field even more quickly than the Sun's own 11-year cycle. Even more interesting is the recent discovery that the star is orbited by a massive planet. It's a hot Jupiter planet, six times the size of Jupiter, but only 1/20th the distance from the Earth to the Sun.

The planet is so close, it has become tidally locked with the star, similar to the way the Moon only shows one face to the Earth. It's possible that the tidal interactions between the star and the planet somehow speed up the surface of tau Bootis, and encourage these magnetic flips.

The astronomers are planning to keep their telescopes firmly targeted at tau Bootis, checking the magnetic field of the star regularly. If it flips again, they'll be ready.

The research was published this week in the British journal Monthly Notices of the Royal Astronomical Society.

Original Source: Institute for Astronomy News Release


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