September 16, 2009

Speaker: Dr. Joan T. Schmelz

Title: Some Like It Hot: Solving the Coronal Heating Mystery

Abstract: The atmosphere of the Sun, the corona, has a temperature greater than 1,000,000 K compared to a mere 5,000 K at the surface. Most astronomers agree that these soaring values are the result of magnetic field energy being converted to thermal energy, but how this is done remains a mystery - the Coronal Heating Mystery. Theoreticians can dream up multitudes of mechanisms to explain the hot corona, but all the fascinating physics takes place on such small spatial scales that observers have no hope of testing these theories directly.

The one exception to this disappointing rule may be related to our new discovery of what is called a "nanoflare signature." A nanoflare is a tiny release of energy that results when a tangled magnetic field realigns into a more normal configuration. If nanoflares heat the corona, then we would expect an ever-present hot component with a temperature of 10 million K, even in quiescent regions of the solar atmosphere.

Using the X-ray Telescope aboard the Hinode (Sunrise) spacecraft, we have detected significant high-temperature emission from an active region that is consistent with nanoflare heating. This high-temperature component is weak, which accounts of the fact that it has not been observed with earlier instruments. If this result can be confirmed, it could provide an additional observation constraint for models competing to explain the heating of the corona and possibly lead to a solution of the Coronal Heating Mystery.