A letter in the journal Nature, published on 11 June, illuminates part of a long-standing mystery about the Sun. Professor Eric Priest from St Andrews University, Dr Carl Foley and Professor Len Culhane from London, together with a team from France and the USA, have discovered that a clash of magnetic fields is likely to be causing the heating of gigantic and super-hot loops of material that arch high above the Sun's surface.
For more that half a century, scientists have known that the surface of the Sun is barely 6000 degrees, but that the overlying atmosphere scorches up to several million degrees. The outer part of this atmosphere forms a halo of eerie light around the Sun during a solar eclipse and consists of giant, super-hot loops that extend high up above the Sun's surface. Using the Soft X-ray Telescope on a Japanese/US/UK space satellite called Yohkoh, which means 'sunbeam', the research team, led by Professor Eric Priest of St Andrews University, has for the first time been able to measure how the temperature varies along such giant loops.
Professor Priest says "Once we had measured the temperature profile, it was exciting to compare the observations with predictions from the three main theoretical models that had previously been put forward. Some felt that the heat is lkely to be dumped at the feet of the loop and then conducted (like the flow of heat along a red-hot poker) to the rest of the loop. Others felt that the heat should be deposited at the summit of the loop, while a third camp predicted a uniform release of heat along the loop."
The comparison of observations and theoretical models shows clearly that the heat is deposited uniformly. The most likely mechanism at present is a clash of magnetic field lines. They tangle like spaghetti in the solar atmosphere and break, causing dozens of explosions that release energy along the loop. These turbulent explosions occur in tiny regions of intense electric current that heat the atmosphere in the same way as the electric current in a light blub or an electric fire.
Further information and hard copies from Professor Eric Priest.
Tel: (work) 01334 463709, (home) 01334 474975.
Lesley Lind. Public Relations Officer. University of St Andrews.
Tel: 01334 462530 Fax: 01334 462590 Email: L.Lind@st-andrews.ac.uk