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Sound waves on distant star reveal sun-like cycle

Astronomers studying sound waves on a distant star have discovered that it has a magnetic cycle similar to our sun's solar cycle.
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Astronomers studying sound waves on a distant star have discovered that it has a magnetic cycle similar to our sun's solar cycle.

The find marks the first time astronomers have detected a star's magnetic cycle using a method called stellar seismology, which monitors the vibrations inside a star. The result could help researchers learn more about the inner workings and evolution of stars, including our own sun.

"This is one piece of a larger puzzle that should help us better understand the sun," said study co-author Travis Metcalfe of the National Center for Atmospheric Research in Boulder, Colo.

Sound on an alien star

The research team, led by Rafael Garcia of the Center for Nuclear Studies in Saclay, France, examined a star known as HD49933. The star is about 100 light-years from Earth in the constellation Monoceros, and is 20 percent more massive than the sun.

Using the CoRoT (COnvection ROtation and planetary Transits) satellite, the astronomers measured the star's acoustic fluctuations, which CoRoT detected as slight variations in light intensity. By analyzing the vibrations, the researchers were able to map out some key details of HD49933's magnetic activity cycle. 

"Essentially, the star is ringing like a bell," Metcalfe said in statement. "As it moves through its starspot cycle, the tone and volume of the ringing changes in a very specific pattern, moving to higher tones with lower volume at the peak of its magnetic cycle."

Astronomers have observed magnetic cycles in other stars before. But they had never done so using stellar seismology, which should prove to be a powerful tool going forward.

"This technique of listening to the stars will allow us to examine potentially hundreds of stars," said study co-author Savita Mathur, also of the National Center for Atmospheric Research, in a statement.

Very short star cycle
The researchers detected "starspots" on HD49933's surface, areas of intense magnetic activity analogous to sunspots. And they found that the star's magnetic activity cycle lasts less than a year. Past surveys of stars have found cycles similar to the sun's 11-year one.

HD49933's short cycle should be intriguing to scientists because it may enable them to observe an entire cycle more quickly. Scientists could thus glean more information about magnetic patterns than they could by observing parts of a longer cycle.

"We're hoping short cycles turn out to be common, so we'll be able to see a full cycle in lots of stars," Metcalfe told

The Next Step
If scientists can observe many stars' magnetic cycles, they might be able to recognize general patterns and figure out what's causing them. This information could shed light on the magnetic processes that go on within the sun, furthering our understanding of its influence on Earth's climate.

Such data may also lead to better predictions of the solar cycle and resulting geomagnetic storms that can cause major disruption to power grids and communication networks.

"Getting a general sense of space weather is a very useful thing," Metcalfe said. "When we only have one star — the sun — to look at, we risk getting a biased view."

And the researchers may soon be able to start getting such a general sense of space weather. They plan to monitor the sound waves of more stars, using both CoRoT and NASA's Kepler space observatory, which was launched in March 2009.

Metcalfe is particularly excited about what Kepler — which will provide continuous data over three to five years from hundreds of stars — may be able to show them.

"Kepler is an unblinking eye," he said. "It's going to be looking for years at a time, and that's very powerful."

The team reports its findings in the Aug. 26 issue of the journal Science.

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