Modelling the Sun’s magnetic field

The important mechanism behind the generation of astrophysical magnetic fields such as that of the Sun has been uncovered by researchers at the Universities of Leeds and Chicago.

The mechanism is known as a ‘dynamo’ and builds on a solution to a reduced set of equations first proposed in the 1950s which could explain the Sun’s regular oscillation, but which appears to break down when applied to objects with high electrical conductivity.

“Previously, dynamos for large, highly conducting bodies such as the Sun would be overwhelmed by small-scale fluctuations in the magnetic field. Here, we have demonstrated a new mechanism involving shear flow, which serves to damp these small-scale variations, revealing the dominant large-scale pattern,” said Professor Steve Tobias, from the University of Leeds’ School of Mathematics and co-author of the research published in Nature.

Scientists have known since the 18th century that the Sun regularly oscillates between periods of high and low solar activity in an 11-year cycle, but have been unable to fully explain how the cycle is generated.

In recent years, it has become more and more important to understand the Sun’s magnetic activity as changes in its magnetic field are responsible for ‘space weather’ phenomena such as solar flares and coronal mass ejections. When this weather heads in the direction of Earth it can damage satellites, endanger astronauts on the International Space Station and cause power grid outages on the ground.

The new mechanism takes into account the ‘shear’ effect of mass movement of the ionised gas (plasma) which makes up the Sun and does so in the extreme parameter regime that is relevant to astrophysical bodies.

Additionally, the mechanism, which was developed through simulations using the high-performance computing facilities at Leeds, could be used to describe other large, spinning astronomical bodies with large-scale magnetic fields, like galaxies.

“The fact that it took 50 years and huge supercomputers shows how complicated the dynamo process really is,” said Professor Fausto Cattaneo, from the University of Chicago’s Department of Astronomy and Astrophysics.

 Reference: Shear-driven dynamo waves at high magnetic Reynolds Number