Magnetic Helicity and the Relaxation of Fossil Fields

نویسندگان

  • A. E. Broderick
  • R. Narayan
چکیده

In the absence of an active dynamo, purely poloidal magnetic field configurations are unstable to large-scale dynamical perturbations and ultimately reconnect away on Alfvénic timescales. Nevertheless, there are a number of classes of stars, including Ap stars, white dwarfs, and neutron stars which are thought to not contain active dynamos and yet do exhibit significant, large scale, surface magnetic fields. Braithwaite & Spruit (2004) have shown via simulations that the external poloidal magnetic field may be stabilized in such systems by a toroidal component in the stellar interior. We present a variational principle for computing the structure of a magnetic field within a conducting sphere surrounded by an insulating vacuum. We find a simple class of axisymmetric solutions parametrized by angular and radial quantum numbers. We discuss the implications that these may have for soft-gamma repeaters and pulsar magnetic field decay.

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تاریخ انتشار 2008