Solar experts detect waves in giant magnetic holes the size of the UK

The Sun is interwoven by a complex network of magnetic field lines that are responsible for a large variety of fascinating features that can be seen in the solar atmosphere. Large, dark regions, which look like holes on the Sun´s surface, mark out areas where the magnetic field breaks through from the Sun´s deep, boiling interior and rises into the very hot solar atmosphere, which is over a million degrees. The largest of these dark regions are often called sunspots and have been studied since their discovery from as early as 364 BC.

Led by Professor Robertus von Fay-Siebenburgen, Head of the Solar Physics and Space Plasma Research Centre (SP2RC) at the University of Sheffield, the team studied a magnetic region of the Sun much smaller than a sunspot, however its size was still many times greater than the size of the UK.

Their research, which was published this week in Astrophysical Journal, has shown that the magnetic hole they observed, which is also known as a pore, is able to channel energy generated deep inside the Sun, along the magnetic field to the Sun´s upper atmosphere. The magnetic field emerging through the pore is over 1,000 times stronger than the magnetic field of Earth.The energy being transported is in the form of a very special form of waves, known as `sausage waves´ which the scientists were able to observe using a UK-built solar imager known as ROSA (Rapid Oscillations of the Solar Atmosphere), which was designed by Queen´s University Belfast and is in operation at the Dunn Solar Telescope, Sacramento Peak, USA. This is the first direct observation of `sausage waves´ at the solar surface. The magnetic hole is seen to increase and decrease in size periodically which is a characteristic feature of the `sausage wave.´

The team of experts, including Dr Richard Morton from the University of Sheffield, as well as Professor Mihalis Mathioudakis and Dr David Jess from Queen´s University Belfast, hope these giant magnetic holes will play an important role in unveiling the longstanding secrets behind solar coronal heating.

This is because the solar surface has a temperature of a few thousand degrees but the solar corona -- the outermost, mysterious, and least understood layer of the Sun's atmosphere -- is heated to temperatures often a thousand times hotter than the surface. Why the temperature of the Sun´s atmosphere increases as we move further away from the centre of energy production, which lies under the surface, is a great mystery of astrophysics. The findings, which demonstrate the transfer of energy on a massive scale, offer a new explanation for this puzzle.

The team now hope to use further similar solar images from ROSA to understand the fine substructure of these massive magnetic holes by reconstructing the images to view what is inside the holes.

Professor Robertus von Fay-Siebenburgen, said: "This is a fascinating new discovery in line with a number of discoveries made in recent years by the team. It is the first time that `sausage waves´ have been detected in the Sun with such detail. Analysing these waves may bring us closer to understanding the physical mechanisms in the atmosphere of a star.