Sun rings like a bell, thanks to solar flares

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London, March 29: Scientists have determined that solar flares in the Sun's outer layers that causes quakes, produce strong oscillations throughout the star the same way as the entire Earth is set ringing for several weeks after a major earthquake. Christoffer Karoff and Hans Kjeldsen of the University of Aarhus in Denmark, came out with the new theory.

According to a report in Nature News, the possibility that post-quake vibrations also occur in the Sun, was first proposed in the 1970s, but has not been demonstrated until now. When Karoff and Kjeldsen studied data from two Sun-watching satellites - the Solar and Heliospheric Observatory and the Geostationary Operational Environmental Satellite, they found that whole-star high-frequency oscillations are more prominent when solar flares are more active, implying a connection between them. These oscillations are thought to be caused by turbulent convection near the solar surface, as hot material rises from deeper down and sinks again as it cools. This motion sets up a kind of noisy background shaking over a wide range of frequencies. The oscillations are observed indirectly: shifts in the frequency of light being emitted by the Sun, caused by movements of the solar surface, can be picked up by these satellites and translated into the shakes that caused them.

"This is just a first observation," said Karoff. "Now the real work starts. We need to figure out how the energy from the flares is delivered into the oscillations," he added.Working this out will entail devising a detailed model of the Sun's structure in the region where flares and sunspots form.

According to Houdek, such follow-up work could shed light on the solar cycle, which is not fully understood. It might also reveal a feedback loop between sunquakes and flares: while the oscillations the team spotted are thought to be a response to flare activity, according to Houdek, the vibrations might also alter the Sun's structure and thus affect the flare-forming process.

According to Karoff, this finding might prove important for our understanding of other stars. It has been very difficult to study whether other stars have a cycle of flares and spots comparable to that of our Sun, simply because they are too far away to see.

But now, by unpicking the signal of oscillations from starlight, one might be able to infer cycles of flare activity on distant stars."If we can see the same kind of signal in other stars, it will suggest that they have flares too," said Karoff.


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