The Sounds of Stars: Ringing Like a Bell

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Question: what is the sound of one star magnetically cycling? If it’s the star affectionately known as HD 49933, a new analysis by scientists at the National Center for Atmospheric Research, collaborating with colleagues in France and Spain, reveals that it sounds for all the world like a bell ringing. The study’s conclusions appeared last week in the “Brevia” section of Science magazine.

Using 187 days of data collected by the Convection Rotation and Planetary Transists (CoRoT) mission, the team studied the sound waves emanating from HD 49933, which was just hanging out, minding its own business, in the constellation Monoceros, a.k.a., the Unicorn. (Head 100 light years out past Earth and turn east when you reach Orion. That’s Monoceros.)

The NCAR scientists employed a technique called stellar seismology: it analyzes acoustic fluctuations to detect the telltale patterns, called “signatures,” that indicate any areas of especially intense magnetic activity — “starspots,” analagous to the sunspots on our own Sun.

What’s interesting is that this “ringing” pattern changes as the star cycles, and when its magnetic cycle peaks, the star emits higher tones at lower volumes, before the cycle starts all over again.

Way back in 1610, Galileo made history when he observed sunspots through his telescope (although some historians credit Thomas Harriot). The Zurich Observatory started regularly monitoring sunspot activity in 1849, by first counting the number of sunspot groups and then the number of individual sunspots.

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We still monitor the solar cycle regularly using similar techniques, augmented with cutting-edge technology. It’s important because this cycle of magnetic activity is what causes changing levels in the radiation we receive on Earth, and also the occasional geomagnetic storms that can knock out power grids and satellites, disrupting communications. (You don’t want the Sun to throw a tantrum unexpectedly and take away Google Street View, do you?)

HD 49933 is of interest because its magnetic cycle is similar to our Sun’s 11-year cycle, except much shorter: less than one year, making this star the fruit fly of astrophysics research. (Many biological studies involve fruit flies because of their very short life spans.) So it doesn’t take as long to observe several cycles and glean more information about any telltale patterns, hopefully shedding light on the magnetic processes taking place deep within the Sun and other stars.

It might even provide yet another tool to identify star systems with the potential to harbor extraterrestrial life, since whatever’s going on magnetically on a star’s surface might influence “habitable conditions.”

But first, they need more data! The next step will be to analyze the acoustic fluctuations of other stars that have passed through CoRoT’s field of view, as well as any data collected form NASA’s Kepler mission, to see if this short magnetic cycle is a fluke, or more common in other stars. Because how can we understand our own Sun more fully, unless we first understand where it fits into the greater stellar family?