Astronomers
have recorded heavenly music bellowed out by the Sun's atmosphere.
Snagging
orchestra seats for this solar symphony would be fruitless, however, as the frequency
of the sound waves is below the human hearing threshold. While humans can make
out sounds between 20 and 20,000 hertz, the solar sound waves are on the order
of milli-hertz--a thousandth of a hertz.
The study,
presented this week at the Royal Astronomical Society's National Astronomy
Meeting in Lancashire, England, reveals that the looping
magnetic fields along the Sun's outer regions, called the corona, carry
magnetic sound waves in a similar manner to musical instruments such as guitars
or pipe organs.
Making
music
Robertus
von Fay-Siebenburgen and Youra Taroyan, both of the Solar Physics and Space Plasma Research Center at
the University of Sheffield, and their colleagues combined information gleaned
from sun-orbiting
satellites with theoretical models of solar processes, such as coronal mass
ejections.
They found
that explosive
events at the Sun's surface appear to trigger acoustic waves that bounce
back and forth between both ends of the loops, a phenomenon known as a standing
wave.
"These
magnetic loops are analogous to a simple guitar string," von Fay-Siebenburgen explained.
"If you pluck a guitar string, you will hear the music."
In the
cosmic equivalent of a guitar pick, so-called microflares at the base of loops
could be plucking the magnetic loops and setting the sound waves in motion, the
researchers speculate. While solar
flares are the largest explosions in the solar system, microflares are a
million times smaller but much more frequent; both phenomena are now thought to
funnel heat into the Sun's outer atmosphere.
The
acoustic waves can be extremely energetic, reaching heights of tens of miles,
and can travel at rapid speeds of 45,000 to 90,000 miles per hour. "These
[explosions] release energy equivalent to millions of hydrogen bombs," von Fay-Siebenburgen
said.
"These
energies are plucking these magnetic strings or standing pipes, which set up
standing waves--exactly the same waves you see on a guitar string," von
Fay-Siebenburgen told SPACE.com. The "sound booms" decay to silence in
less than an hour, dissipating in the hot solar corona.
Solar
physics
The musical
finding could help explain why the Sun's corona is so hot.
While the
Sun's surface is a steamy 10,000 degrees Fahrenheit (5,538 degrees Celsius), plasma
gas in the corona soars to more than 100 times hotter.
"How can
the atmosphere above the surface of the Sun be hotter if nuclear fusion happens
inside the Sun?" von Fay-Siebenburgen said. If astronomers can get a clearer
picture of what's going on inside these magnetic loops in the Sun's atmosphere,
they have a better chance of finding the answer.
Another
recent study using images from Hinode's telescope revealed twisted
magnetic fields along the Sun's surface, which store huge amounts of
energy. The magnetic fields can snap like a rubber band; when they do, they
might release energy that could heat up the corona or power solar eruptions and
coronal mass ejections, the researchers say.
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