20 Aug 10 – (Excerpts) – Researchers at the University of Dundee have made a breakthrough in the study of magnetic fields, which enhances our understanding of how stars, including the Sun, work.
The team from the Magneto-hydrodynamics research group in the School of Engineering, Physics and Mathematics used state-of-the-art computer simulations of evolving plasmas in the Sun’s atmosphere.
The neat pattern of magnetic “field lines” from a bar magnet is well-known from school physics experiments.
But magnetic fields are not always so ordered. Telescopic pictures of the Sun’s lower atmosphere taken in extreme-ultraviolet light, often reveal braiding and tangling of the field. The fact that the magnetic field lines are tangled like spaghetti means that the plasma in the Sun’s atmosphere is not free to move around however it pleases and that vast quantities of energy can be locked in the magnetic field, because tangled fields have more energy than ordered fields.
Scientists believe that this energy is responsible for heating the Sun’s atmosphere to million-degree temperatures, but how this works in detail is a longstanding puzzle in solar physics.
‘These structures are not static,” said Dr Gunnar Hornig, one of the paper’s authors. “They evolve because the Sun is not a rigid body but essentially a plasma ball of gas. It kind of boils, and the motion on the surface changes these magnetic structures. They start to move them around and sometimes the braiding is increased. And if certain critical conditions are met then these structures start to relax to something simpler.
‘If you take a twig of a branch and start to twist it, then at some point it starts to break and the individual fibres break up. Something similar happens to these magnetic fields. Where it differs is that the evolutions we have been studying allow the broken fields to combine to form new structures.’
Provided by University of Dundee
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