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In this week's Astrophysical Journal, an article appears that may resolve the long standing problem of why the Sun's atmosphere - the corona - passes from about 6000°C at the photosphere to over a million degrees at greater altitudes.
It has long been thought that the solar magnetic field is responsible for the heating, but none of the mechanisms so far proposed has proven completely satisfactory. But now the results of a team from the University of Sheffield and Queen's University Belfast (with lead author Richard Morton) has shown how large quantities of magnetic energy are transported into the corona through solar pores.
The energy is transported in the form of waves in the magnetic field, called "sausage waves".
These waves emerge from the deeper layers of the Sun, along the magnetic field lines, and pass into the corona through the pores, causing them to periodically expand and contract, just as if a string of sausages were being pulled through them.
The team was able to study this phenomenon using a purpose-built camera called Rapid Oscillations of the Solar Atmosphere (ROSA), mounted on the Dunn Solar Telescope in Sacramento Peak, USA. (The above illustration shows the size of the UK in comparison to a small sunspot group and gives some idea of the resolution attainable with ROSA.)
According to Robertus von Fay-Siebenburgen (Head of the Solar Physics and Space Plasma Research Centre at the University of Sheffield), further higher resolution imaging of the solar pores through which the waves pass could bring us considerably closer to understanding the physical mechanisms that regulate stellar atmospheres.
Although energy appears to be transported into the corona through the solar pores, it is likely that this is just part of a larger picture of coronal heating, given that solar pores (the precursors of sunspots) are few and far between at any given moment, are only a few thousand kilometers in diameter and last for only several hours to a few days. |
