Monday, November 18, 2013

The Sun and one of physics' biggest unsolved problems

The sun with a coronal hole (the large dark region at the bottom). Credit: NASA

Daniel Wolf Savin and Michael Hahn have been fascinated by the universe since they were boys.

For Savin, a senior research scientist in the Columbia Astrophysics Laboratory, discovering Albert Einstein at age 12 spurred the desire to "learn everything about the universe."

Years later, Hahn, an associate research scientist who grew up 40 miles from Savin's home town in Connecticut, started gazing at the stars as a teenager; he eventually became president of the astronomy club at his alma mater, Carnegie Mellon.

Now the two have made a big leap toward cracking one of the biggest mysteries in astrophysics—why the corona, or plasma surrounding the sun, is so much hotter than the sun's surface.

The coronal heating problem, as it is known, is important because the corona is the source of solar wind, which is responsible for the northern and southern lights and can also disrupt telecommunications and power grids.

"Satellites can be slowly pushed out of their orbits if they're deflected by the solar wind so if we can better understand the cause, we can create better models for space weather," says Savin, referring to conditions beyond the atmosphere.

Scientists have proposed two main theories to explain why the temperature of the gas in the corona, which lies above the solar surface, soars to over 1 million degrees Kelvin even though the surface of the sun is a relatively cool 6,000 degrees. (The center of the sun is 15 million degrees.)

This unexpected phenomenon has puzzled researchers since 1939, when scientists first discovered the temperature difference; it's as if a flame were coming out of an ice cube.

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