Spiky
bursts of plasma called spicules swirl around the surface of the sun.
Millions erupt every moment, spurting solar material some 6,000 miles
high at speeds of about 60 miles per second.
“These things are very violent,” said Bart De Pontieu, a research scientist with Lockheed Martin Solar and Astrophysics Lab
in Palo Alto, Calif. “The gas in spicules is about 10,000 degrees and
they travel the length of California in just a minute or so.”
Scientists
have studied spicules for decades, but were not sure how the plasma
jets formed. Now, Dr. De Pontieu and his colleagues think they have
solved the searing mystery. They published their findings Thursday in
the journal Science.
Using
data gathered by high-powered land and space telescopes, they created a
computer simulation that reconstructed the conditions between the sun’s
surface and its atmosphere, where spicules form.
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Powerful
magnetic fields are created in the interior of the sun. There, the high
density keeps them tangled and tamed. But near the surface, the
magnetic fields can use neutral particles, atoms that do not carry an
electric charge, to diffuse into the sun’s atmosphere. The fields enter a
reddish layer called the chromosphere where their violent nature is
unleashed.
“It’s a sling shot effect,” said Mats Carlsson, a professor of astrophysics at the University of Oslo in Norway, and co-author of the paper.
The
density in the chromosphere is significantly lower than in the sun’s
interior, so the magnetic fields are no longer suppressed and are able
to straighten out. As they unwind and release their tension, they fling
hot plasma at incredible speeds, creating the spicules. The spicules
surge thousands of miles high, passing through the chromosphere and into
the sun’s corona before collapsing.
To
create a computer simulation that accurately reflected what was
happening on the sun, Dr. Carlsson said they needed to incorporate the
effects of neutral particles. In earlier simulations they did not
differentiate neutral particles from charged particles in the sun. Those
models made it seem as if the edge between the sun’s atmosphere and
surface was fully electrically charged.
“We
had an absence of spicules,” said Dr. Carlsson. “In our previous model
we had one instead of the millions you have in the sun.”
But
when they plugged distinct neutral particles into their simulation,
they produced a model that had the same features seen on the sun.
Juan Martínez-Sykora,
an astrophysicist with Lockheed Martin as well as the Bay Area
Environmental Research Institute and lead author of the study, said the
team’s next steps were to see if the spicules played a part in fueling
the sun’s corona and solar winds. If so, their simulation may help
answer the million-degree mystery of what makes the corona so hot.
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