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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