brian0918 writes "Until now, the assumption has been that the rapid spin of a pulsar comes from the spin of the original star. The problem was that this only explained the fastest observed pulsars. Now, researchers at Oak Ridge have shown that the spin of a pulsar is determined by the shock wave created when the star's massive iron core collapses. From the article: 'That shock wave is inherently unstable, and eventually becomes cigar-shaped instead of spherical. The instability creates two rotating flows — one in one direction directly below the shock wave and another, inner flow, that travels in the opposite direction and spins up the core. The asymmetrical flows establish a 'sloshing' motion that accounts for the pulsars' observed spin velocities from once every 15 to 300 milliseconds.'"