Sun's Ripples Reveal Clues to the Core

The core ofthe Sun holds secrets into how it and the planets formed billions of years ago,but the bright solar surface obscures the view of its heart.

Now after a30-year search, astrophysicists may have detected hints of ripples on thesurface, just a few yards high, that could finally help shed light on the mysteriouscore.

The resultssuggest theSun's core rotates more slowly than theorists have predicted.

Longsearch

Astronomersfirst detected waves on the solar surface 30 years ago. Soaring miles high, those"p-mode" waves are generated by sound running through the star. They hintedat the existence of far more subtle ripples driven by gravity. These"g-mode" waves are believed to occur whengas churning below the surface plunges even deeper and collides with densermaterial, sending ripples propagating through the interior and up to thesurface--the equivalent of dropping a stone in a pond.

Scientistswanted to detect g-mode waves since they pass through the Sun's mysteriousheart and carry vital information concerning internal activity. For instance,the speed at which the solar core rotates is uncertain. Knowing this detailcould shed light on the birth of the entire solar system, because it representsthe hub of rotation for the dusty cloud of matter that eventually formed thesun and planets.

Unfortunately,g-modes are badly degraded during their passage tothe solar surface, and by the time they reach the exterior, they are littlemore than ripples a few yards high.

Tomake matters harder, the g-modes take between two and seven hours to rise andfall just once, which means astronomers are faced with having to detect a swellthat moves just a few millimeters per second at most.

Finally, success

Now,however, an international team of astronomers employing the ESA-NASA Solar andHeliospheric Observatory (SOHO) may have finally caught glimpses of theselong-sought waves, findings detailed online May 3 in the journal Science.

Thekey was the telescope's Global Oscillation at Low Frequency (GOLF) instrument.This device looks for bright, distinctive signals given off by sodium vapor,allowing researchers to measure ripples on the Sun with great sensitivity. Theg-modes are very distinct from the p-modes in terms of both size and the speedat which they rise and fall.

Theinstrument cannot distinguish lone g-modes. Instead, astrophysicist RafaelGarcia at DSM/DAPNIA/Service d'Astrophysique in France and his colleagues lookedfor the signature of a large number of these oscillations from 10 years of GOLFdata.

"Byanalogy, imagine that the Sun was anenormous piano playing all the notes simultaneously. Instead of looking for aparticular note--middle C, for instance--it would be easier to search for all theC's, from all the octaves together," Garcia said. "So that's what welooked for, the cumulative effect of several g-modes."

What was learned

Theway the g-modes got distorted as they passed through the Sun have given thefirst hints of the core's rotation speed. The surface of the Sun rotates atdifferent rates depending on location, with the equator spinning faster (about 25days) than the poles (roughly 36 days).

"Thecore of the Sun seems to rotate about three to five times faster onaverage," Garcia told LiveScience.

Currenttheories of solar formation suggest the original cloud of matter that gave riseto the solar system had a high rate of rotation, a remnant of which "couldexist in the deepest regions of the Sun," Garcia said. "It seems thatthe solar core rotation is slower than expected by those theories," headded.

Garcianoted a magnetic field leftover from the solar system's formation could havecontributed to slowing down the solar core. A new generation of instruments nowbeing built that can measure individual g-modes--for instance, "the GOLFNew-Generation prototype that could fly in the DynaMICCS spacecraft presentedinside the Cosmic-Vision 2015-2025 ESA program"--could help provide theinsight needed to explain the mysteries of the solar core, he said.

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