Evolution of the Magnetic Field Structure of the Crab Pulsar

Magnetic Crab Since pulsars—highly magnetized rotating neutron stars—were discovered 45 years ago, the evolution of their magnetic field structure has been subject to much theoretical conjecture. However, observational evidence has been sparse. Now Lyne et al. (p. 598) report high-precision measurements, spanning more than two decades, that reveal the systematic evolution of the radiation pattern of the pulsar in the Crab Nebula, one of the youngest neutron stars known. Long-term measurements show the systematic evolution of the radiation pattern of one of the youngest neutron stars known. Pulsars are highly magnetized rotating neutron stars and are well known for the stability of their signature pulse shapes, allowing high-precision studies of their rotation. However, during the past 22 years, the radio pulse profile of the Crab pulsar has shown a steady increase in the separation of the main pulse and interpulse components at 0.62° ± 0.03° per century. There are also secular changes in the relative strengths of several components of the profile. The changing component separation indicates that the axis of the dipolar magnetic field, embedded in the neutron star, is moving toward the stellar equator. This evolution of the magnetic field could explain why the pulsar does not spin down as expected from simple braking by a rotating dipolar magnetic field.

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