Light Cylinder

The light cylinder of a rotating magnetized object is the imaginary cylindrical surface at the radial distance where a particle corotating with the object would have to travel at the speed of light to keep up. For a pulsar rotating with angular velocity Ω, the light cylinder radius is R_c = c/Ω — roughly 4.8 × 10^4 km for a typical one-second pulsar, shrinking to just a few hundred kilometers for millisecond pulsars. Within the light cylinder, magnetic field lines can close and plasma can corotate with the star; beyond it, the field lines must open, creating the relativistic particle wind that drives pulsar wind nebulae. The light cylinder is not a physical boundary but a causal one: it marks where the rigid rotation assumption breaks down and the magnetosphere transitions from corotating plasma to an outgoing wind.