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Magnetic dipole braking (or magnetic dipole spin-down or just magnetic braking) is the tendency for the rotation of rotating magnetic field to slow if it is embedded within a non-rotating magnetic field. Magnetic dipole radiation is generated in the process, which carries away the angular momentum and kinetic energy (KE). Such braking is presumed to contribute to the observed slow reduction of the rotation of pulsars (pulsar braking), likely to be most significant just after the neutron star's birth.
The rate of energy released by a pulsar's reduction in rotation is termed its spin-down luminosity, and the time it takes to spin down is the spin-down time (or spin-down timescale) calculated as the rotation's KE (spin-down energy) divided by the spin-down luminosity.
Such magnetic dipole braking has been considered a mechanism that causes pulsar's observed reduction in rotation, but a competing theory presumes the reduction occurs as angular momentum is carried off by the pulsar's stellar wind (wind braking).