Quantcast

Sun’s Magnetic Secret Revealed

January 22, 2008

Powerful
magnetic waves have been confirmed for the first time as major players in the
process that makes the sun’s atmosphere strangely hundreds of times hotter than
its already superhot surface.

The
magnetic waves — called Alfven waves — can carry enough energy from the sun’s
active surface to heat its atmosphere, or corona.

“The
surface and corona are chock full of these things, and they’re very
energetic,” said Bart de Pontieu, a physicist at the Lockheed Martin Solar
and Astrophysics Laboratory in California.

The sun
contains powerful heating and magnetic forces which drive the temperature to
tens of thousands of degrees at the surface — yet the quieter corona wreathing
the sun reaches temperatures of millions of degrees. Scientists have speculated
that Alfven waves act as energy
conveyor belts to heat the sun’s atmosphere, but lacked the observational
evidence to prove their theories.

De Pontieu
and his colleagues changed that by using the Japanese orbiting solar
observatory Hinode to peer
at the region
sandwiched between the sun’s surface and corona, called the chromosphere.
Not only did they spot many Alfven
waves, but they also estimated the waves carried more than enough energy to
sustain the corona’s temperatures as well as to power the solar wind (charged
particles that constantly stream out from the sun) to speeds of nearly 1 million
mph.

However,
the chromosphere findings alone could not prove the waves carried their energy
into the sun’s atmosphere.

“If you
observe waves in the chromosphere, that doesn’t mean they can get to the
corona,” De Pontieu told SPACE.com.

Some waves
may get reflected back down to the sun instead of passing through the
transition region between the surface and atmosphere. Waves that reach the
corona also become more difficult to detect using current instruments, thanks
to the long line-of-sight.

De Pontieu’s
group turned to researchers at the University of Oslo, Norway, who had created
a computer
simulation
representing part of the sun. Once they knew what to look for,
the researchers found magnetic waves within the simulation of the corona that
strongly resembled the Alfven waves directly observed in the chromosphere.

Even as the
simulations helped establish Alfven waves as energy carriers for the sun’s
atmosphere and solar wind, the new observational findings will help modelers
create improved sun simulations.

“It goes
back and forth — we learn from simulations, they learn from us,” said De
Pontieu.

Many
mysteries remain about the sun’s restless activities. De Pontieu’s group
focused on Alfven waves generated by the sun’s heat turbulence, but other
researchers examined Alfven waves generated when the sun’s magnetic field lines
stress and snap back together like invisible magnets. That reconnection force
also creates jets of X-rays that shoot outwards from the sun, as captured by Hinode’s
instruments.

Scientists
still don’t know which source of Alfven waves plays a more important role in
the heating the sun’s atmosphere, but can use the latest findings as a stepping
stone.

“We need to
study both more, to see which one dominates,” noted De Pontieu. “But it’s nice
for people to know that Alfven waves can do the job.”


Source: imaginova



comments powered by Disqus