Clues to the Cause of the Solar Corona's Extremely High Temperature Discovered!
For 70 years, the question of how the corona, located above the Sun's surface and responsible for the phenomena we call solar winds, is much hotter than the Sun's surface, remained unresolved. While the Sun's surface is 6,000 degrees Celsius, a few hundred kilometers above the surface is 1 million degrees Celsius.
Dr. Michael Hahn and Daniel Wolf Savin of the Columbia University Astrophysics Laboratory in New York explained that the magnetic field at the polar region of the corona may be accumulating enough energy to heat the corona, and even transporting a significant portion of the energy to lower altitudes, allowing the heat to spread throughout the corona. This observation could explain the 70-year-old Corona Heating Problem, known as the Sun's Coronal Heating Problem, which is much higher than the Sun's surface temperature.
Hahn and Savin analyzed information from superultraviolet images taken by the Japanese spacecraft Hinode. They examined one of the magnetic channels in the Sun's corona, where the Sun's magnetic field forms. Their research was published in The Astrophysical Journal.
The easiest way to understand the Coronal Heating Problem is to imagine an ice cube erupting with flames (and this normally doesn't happen, it shouldn't). A similar effect occurs in the Sun. Nuclear fusion at the Sun's center causes the core to heat up to 15 million degrees Celsius. As we move away from this fiery furnace and reach the Sun's surface, the temperature drops to 6,000 degrees Celsius. However, just outside the Sun's surface, in a region called the "corona," the temperature suddenly jumps to 1 million degrees Celsius. This temperature jump has puzzled scientists since 1939.
Two theories attempt to explain this mystery. The first is based on the idea that magnetic field loops emanate from the solar surface, superheating surrounding regions. The other is based on the idea that heat waves originating beneath the solar surface carry magnetic energy, which accumulates and is released in the corona. Observations indicate that both theories occur constantly on the solar surface. However, scientists have so far only been exploring whether one of these theories is sufficient to explain the problem.
According to Hahn and Savin's research, magnetic waves must be the answer. This discovery also raises new questions: the main one being what dampens these waves. Through their research, Hahn and Savin will attempt to answer this question.
Sources:
Science Daily-Astronomers Find Clues to Decades-Long Coronal Heating Mystery
- Colombia Astrophysics Laboratory
Observational Quantification of the Energy Dissipated
by Alfv´en Waves in a Polar Coronal Hole:
Evidence that Waves Drive the Fast Solar Wind.
M. Hahn1 and DW Savin1
