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Neutron Stars : Magnetism vs Gravity
WHY do neutron stars have such strong magnetic fields?
Conservation of magnetic flux of the collapsing stellar core
- ∫ B.ds (over surface of the star) = constant
- Radius of the star collapses from ~ 5x108 to 1x104 metres
- Hence, surface magnetic field increases by a factor of ~ 2.5x109
- ~ 2.5x1011 Gauss field for the neutron star !
Neutron stars also have very strong gravity : g = 1012 m/s2 ;
however, in the magnetosphere, electromagnetic forces dominate over gravity :
- Fgr = mg ~ 10-18 Newton ; Fem = e V B ~ 10-5 Newton
- (for a single electron of mass m and charge e )
- Hence, the electromagnetic force is 1013 times stronger than gravity !!
The magnetic field thus controls the distribution of plasma in the pulsar magnetosphere and also the physics of its acceleration and subsequent production of electromagnetic radiation