Powerful Magnetic Waves Help Make Sun's Atmosphere Hotter Than Sun Itself

By Joseph Castro | July 29, 2011 8:34 am

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What’s the News: An international team of researchers, led by the National Center for Atmospheric Research, has learned that large magnetic waves are partly to blame for the Sun’s immensely hot corona. The study, published in the journal Nature, also suggests that the waves could be the driving force behind the solar wind.

What’s the Context:

  • The corona is the outer atmosphere of the Sun, which is only visible by the naked eye during a solar eclipse. It has fascinated solar physicists for decades because it’s over 20 times hotter than the surface of the sun—you’d expect that the further away you get from a heat source, the cooler it gets.
  • One possible explanation for the corona’s extreme temperature has been Alfvén waves, first proposed by Nobel Prize-winner Hannes Alfvén. Alfvén waves are high-speed magnetic oscillations thought to travel along the Sun’s magnetic field lines, transporting large amounts of energy (in the form of heat) from the surface to the corona in the process. In 2007, researchers finally observed these waves, but the waves were too sporadic and weak to explain the corona’s temperature.

How the Heck:

  • Using instruments at NASA’s Solar Dynamics Observatory, scientists examined spicules—short-lived jets of hot, ionized gas—expelled from the Sun. Because these plasma jets also move along the star’s magnetic field lines, the researchers could determine the energy of the Alfvén waves as they bent the spicules.
  • The team used statistical models to interpret data from X-ray and UV snapshots of the jets and waves. They found that Alfvén waves are energetic enough to heat much of the Sun’s corona, as well as drive the acceleration of the solar wind, a stream of electrically charged particles traveling out of the corona at about 1 million miles per hour.

Not So Fast:

  • While the study revealed that Alfvén waves are over 100 times stronger than previously thought, they still didn’t have enough energy to heat the hottest portions of the corona. There may be some other mechanism adding to the corona’s temperature, or more mysteries to unravel about the Alfvén waves.
  • The researchers still don’t know exactly how the magnetic waves are able to transmit all of that energy.

(via Popular Mechanics)

Image courtesy of NASA Goddard Photo and Video / Flickr


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