Saturday, 15 December 2012

Origin of the magnetic field of neutron stars

The strong magnetic fields in neutron stars are supposed to come from magnetic flux conservation. If we have:



PhiB=intBdS=const



where PhiB is the magnetic field flux, B is the magnetic field strength, and dS is the elemental closed surface; then, this integral is constant through the surface.



If we consider the star surface over which take the integral, than



S=4piR2



where R is the star radius. This can be translated, altogether with the magnetic flux conservation law, as:



Bf=Bi(fracRiRf)2



where i and f are the indices for initial and final stages.
We know that the star implodes from a whatever star size to sim10 km. So the radii ratio is huge. You just need a starting magnetic field of 10100 G, to get a final magnetic field of the order of 1012 G, that is typical in neutron stars.

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