Since the discovery of the first pulsar in 1967, astronomers have struggled to explain why they travel so fast. In a paper to be published in the 9 December issue of Physical Review Letters , Alexander Kusenko and Gino Segre of the University of Pennsylvania argue that the velocity kick that propels pulsars through space may be the result of a flood of neutrinos rushing out from the collapsing core, but in a nonuniform way, like the air from a balloon. When a massive star explodes, it can temporarily outshine a galaxy of several hundred billion suns. But even more staggering is the energy released in the form of neutrinos, which can briefly exceed the luminosity of all stars in the known galaxies. But the neutrino emission may not be uniform-and this may be what causes the kick.
Neutrinos usually pass through normal matter.
But the hot interior of a recently-formed neutron star is so dense that neutrinos begin to interact with it. It turns out that the distance over which these flips occur depends on the direction of the magnetic field in that region of the neutron star, so that on one side, far more tau neutrinos will emerge from its hotter inner regions.