What causes a pulsar to emit radio-frequent pulses?

Answer 1

This is not well understood, but its thought the process has to do with the large magnetic field at the surface of the neutron star. The radio pulses (and sometimes the pulses are observed in other parts of the spectrum, like visible light, for example), apparently arise near the polar cap of the magnetic field and are beamed out like a light house beacon. As the beacon sweeps across our position, we detect the "pulse."..

Answer 2

Pulsars are rotating neutron stars which emit detectable electromagnetic radiation in the form of radio waves. The radiation intensity varies with a regular period, believed to correspond to the rotation period of the star. Pulsars also exhibit a so-called lighthouse effect, which occurs when the light and other radiation from a pulsar are only seen at specific intervals and not all of the time. Werner Becker of the Max-Planck-Institut für extraterrestrische Physik recently said,

“ The theory of how pulsars emit their radiation is still in its infancy, even after nearly forty years of work..

May be these have some natural radio active sources.

Answer 3

HERE'S SOME INFO ---

http://en.wikipedia.org/wiki/Pulsar