Global oscillations of sound waves in the sun are correlated with solar flares (represented by the solar X-ray flux in the right panel). The color-coding represents the strength of the oscillations. Credits: SOHO/VIRGO (ESA & NASA).
Mighty eruptions on the sun trigger bursts of sound waves that ripple across the fiery ball of gas, astronomers say.
The finding, which will be published in the May 1 issue of the Astrophysical Journal Letters, comes from data collected with the Solar and Heliospheric Observatory (SOHO), a joint venture between NASA and ESA.
Astronomers have known that sound waves constantly trek toward the sun's interior, producing a background "ringing" of sorts. As they move through the sun's plasma, the sound waves take on a pulsing pattern of five minutes, and hence are called five-minute oscillations. They are also called starquakes.
"We see the plasma moving toward us, receding from us, moving toward us, receding from us," said Bernhard Fleck, SOHO project scientist at NASA Goddard Space Flight Center in Greenbelt, Md. "It's like waves in the ocean."
Until now, scientists thought the oscillations were caused by churning gas near the interior of the sun. And the churning gas does play a role, but there's more.
These global oscillations can be thought of as the sound you would get from a bell sitting in the middle of the desert that is constantly tapped by random sand grains.
Now Christoffer Karoff and Hans Kjeldsen, both at the University of Aarhus, Denmark, find that every once in a while somebody bangs a hammer on the bell ? bing ? causing a stint of intense sound waves. That hammer, they found, comes from powerful solar flares.
"The signal we saw was like someone occasionally walking up to the bell and striking it," Karoff said, "which told us that there was something missing from our understanding of how the sun works."
They discovered a strong correlation between an increase in the number of solar flares and a bump in the strength of the five-minute oscillations.
"This large flare on the sun, this disturbance, shakes the sun and then it keeps vibrating for some time with these global oscillations," Fleck told SPACE.com.
A similar phenomenon occurs on Earth in the aftermath of large earthquakes. For example, after the 2004 Sumatra-Andaman Earthquake, the whole Earth rang with seismic waves for several weeks.
Now the researchers hope to figure out more about exactly how the flares cause the oscillations.
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