INTRODUCTIONBLACK HOLESNEUTRON STARS AND PULSARSHOW THEY FORMHOW WE DETECT THEMBIBLIOGRAPHYQ & A PAGESRELATED LINKSPRINTOUTBOOKSNeutron stars are very dense and spin very fast and are typically only 10-15 km in radius. Because neutron stars form from burnt-out stars, they do not glow. The collapse of the star causes the matter to be converted into mostly neutrons, hence the name neutron star.
Some neutron stars emit radio waves that pulse on and off. These stars are called pulsars. Pulsars don't really turn radio waves on and off--it just appears that way to observers on Earth because the star is spinning. What happens is that the radio waves only escape from the North and South magnetic poles of the neutron star. If the spin axis is tilted with respect to the magnetic poles, the escaping radio waves sweep around like the light beam from a lighthouse. Far away on Earth, radio astronomers pick up the radio waves only when the beam sweeps across the Earth.
These pictures are based on a drawing in Zeilik, M. and J. Gaustad. Astronomy: The Cosmic Perspective. New York: John Wiley & Sons, Inc, 1990, p 544.