Astrophysical Fluid Dynamics at Leeds

Astrophysical Fluid Dynamics at Leeds

Dr Adrian Barker University of Leeds

Here are a few science hightlights since our project started on 1st April 2022.

Neutron stars are the strongest magnets in the Universe. Their extraordinary magnetic fields are formed during the supernova explosion and continue evolving when neutron star crust solidifies. Magnetic fields of neutron stars are so strong that they control how heat is transported within the crust forming complicated surface thermal patterns. In this project we investigate different initial magnetic field configurations and evaluate their impact on X-ray observations. We study in details the off-centred dipole configurations and check if the amount of dipole shift could be measured using spectral and timing observations. A figure is attached below from simulations by Andrei Igoshev on DIaL3.

The Earth’s magnetic field is known to reverse polarity on average a few times per million years.

Other planets with magnetic fields may well reverse polarity too, but our lack of understanding of the reversal mechanism has prevented us from answering the question of whether they actually do reverse.

A major problem is that the current numerical dynamo models which do reverse are strongly influenced by the inertial term in the equation of motion (Rossby number order 1), but this is term is actually small in planetary dynamos on the long reversal timescale. We are exploring whether reversing dynamo models are possible when the Rossby number is small (the situation in most planetary interiors), and whether large Peclet number convection (the Peclet number really is large in most planetary interiors) can provide the fluctuations necessary to get reversals. The answer is yes, we have a new class of dynamo models which do reverse at low Rossby number if the Peclet number is large enough.

The two images show the dipole moment as a function of magnetic diffusion time produced by Chris Jones. The left one at Prandtl number 30 has Peclet number 248. It fluctuates but does not change sign with time. The second image on the right has a larger Peclet number, 317, which is just above critical and does reverse the sign of the dipole moment.