Sun's magnetic field may originate closer to the solar surface
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[May 23, 2024]
By Will Dunham
WASHINGTON (Reuters) - The sun's magnetic field, which causes solar
storms like the one that hit Earth this month and produced beautiful
auroras, may originate at shallower depths in the star's interior than
previously thought, according to researchers.
The sun's outer 30% is comprised of an "ocean" of churning gases
plunging more than 130,000 miles (210,000 km) below the solar surface.
The research, comparing new theoretical models to observations by the
sun-observing SOHO spacecraft, provides strong evidence that its
magnetic field is generated near the top of this ocean - less than 5%
inward, or about 20,000 miles (32,000 km) - rather than near the bottom,
as long hypothesized.
In addition to providing insight into the sun's dynamic processes, the
findings may improve the ability to forecast solar storms and guard
against potential damage to electricity grids, radio communications and
orbiting satellites, the researchers said.
Most stars have magnetic fields, apparently generated by the motion of
super-hot gases inside them. The sun's ever-changing magnetic field
drives the formation of sunspots - shifting dark patches - on its
surface and triggers solar flares that blast hot charged particles into
space.
"The top 5% to 10% of the sun is a region where the winds are perfect
for making abundant magnetic fields through a fascinating astrophysical
process," said Geoffrey Vasil, an applied and computational
mathematician at the University of Edinburgh in Scotland and lead author
of the study published on Wednesday in the journal Nature.
This process involves rotational flow patterns of super-hot ionized -
electrically charged - gases called plasma inside the sun.
The precise mechanisms behind how the sun generates its magnetic field -
the solar dynamo, as the scientists call it - has remained an unsolved
problem in theoretical physics. These researchers hypothesize that these
flow patterns are the key.
"If the plasma which constitutes the sun was completely stationary, we
know the sun's magnetic field would decay in time, and before long,
there would be no sunspots or other solar activity. However, the plasma
in the sun is moving around, and that motion is able to regenerate and
maintain the sun's magnetic field," said theoretical physicist and study
co-author Daniel Lecoanet of Northwestern University in Illinois.
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The Sun emits a solar flare February 22, 2024, in this image
captured by NASA's Solar Dynamics Observatory. NASA/SDO/Handout via
REUTERS/File Photo
The solar magnetic field ebbs and flows in a distinct pattern, with
sunspots - regions with very large magnetic fields - emerging and
then vanishing every 11 years, making the sun, as Vasil called it,
"a giant magnetic clock."
"But we have yet to find the full story about how it happens.
Complex interacting fluid motions (in this case, the solar plasma)
ultimately drive a dynamo, but we can't yet explain the details,"
Vasil added.
Italian polymath Galileo carried out in 1612 the first detailed
observations of sunspots using telescopes he invented. American
astronomer George Hale in the early 20th century determined that
sunspots were magnetic.
"And we're still scratching our heads about these pesky sunspots,"
Vasil said.
A strong solar storm that reached Earth this month caused bright
auroras in the skies, though Earth's technological infrastructure
remained unscathed.
"Occasionally, a group of sunspots explodes and launches a billion
tons of hot charged particles toward Earth, like what happened last
week," Vasil said.
But a powerful solar storm like one that occurred in 1859 called the
Carrington Event could cause trillions of dollars in damage and
leave hundreds of millions of people without power, the researchers
said.
"You can think of magnetic fields as being like rubber bands. The
motions near the surface of the sun can stretch out the rubber bands
until they break. The breaking magnetic field can then launch
material outward into space in what is called a solar storm. If
we're unlucky, these storms can be launched toward the Earth and can
cause significant damage to our satellites and power grid," Lecoanet
added.
(Reporting by Will Dunham; Editing by Lisa Shumaker)
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