July 9, 2013
Magnetic Waves Responsible For Keeping Sun’s Corona Heated
Lee Rannals for redOrbit.com - Your Universe Online
Astronomers at the 44th meeting of the Solar Physics Division (SPD) of the American Astronomical Society are shedding light on the Sun's coronal heating mystery.
The team found evidence magnetic waves in a polar coronal hole contain enough energy to heat the corona and deposit most of their energy at sufficiently low heights for the heat to spread throughout the corona. Their observations help answer a 60-year-old solar physics mystery about the unexplained temperature of the Sun's corona, which has been likened to a flame coming out of an ice cube.
Nuclear fusion in the center of the Sun heats our neighboring star's solar core to 15 million degrees. If you move away from this area and arrive at the surface of the Sun the gas has cooled to about 6,000 degrees. However, the temperature of the gas in the corona, above the solar surface, soars back up to over 1 million degrees.
Drs. Michael Hahn and Daniel Wolf Savin, research scientists at Columbia University's Astrophysics Laboratory in New York, used observations taken from the Extreme Ultraviolet Imaging Spectrometer on board the Japanese satellite Hinode. They used data based on a polar coronal hole, which is a region of the Sun where the magnetic field lines stretch from the solar surface into interplanetary space.
Scientists have come up with two dominant theories to explain the mystery behind coronal heating. One theory says the heating is due to the loops of the magnetic field, claiming as they stretch across the solar surface and snap, they release energy. The other theory says magnetic waves emanating from below the surface causes the heat. However, previous observations haven't been able to pinpoint which theory to follow, until now.
The Columbia University team's observations show magnetic waves are the answer. However, this determination opens up a realm of further questions, including what causes the waves to damp. The team plans to perform new observations in order to try to address this issue.
Scientists at the same meeting have pointed to magnetic fields as a way to predict where sunspots will emerge. A team from NorthWest Research Associates (NWRA) and the Max-Planck-Institut fur Sonnensystemforschung (MPS) used data from the Global Oscillations Network Group (GONG) and the Michelson Doppler Imager (MDI) to help predict sunspots at least a day in advance, which could ultimately help scientists better understand space weather.
"We've shown that careful research using the visible part of the Sun can indeed tell us about what is happening underneath; these results will be a guide for further research, and ultimately improve our understanding of the Sun and all stars," said Senior Research Scientist Dr. K. D. Leka.