Instead, they explode as supernovae. Typically, in the nucleus of the exploding supernova there is more mass that in the whole Sun. Pulsars emit radio waves in two relatively narrow and opposite beams which rotate together with the pulsar like the beam of a lighthouse. When the radio beam sweep the Earth, it is registered by big radiotelescopes as a short radio pulse. Typical rotational periods of pulsars range from milliseconds to seconds and are extremely steady.
Pulsars are thus very accurate celestial clocks.
Indeed, as accurate as the best man made atomic clocks. The precision of pulsars' clock allows measurements of some of the properties of the neutron stars with an unprecedented accuracy. This may have far reaching consequences for testing the theory of elementary particles. A dice made of the neutron star matter would be as heavy as Mont Blanc - about a billion tons. It is therefore quite obvious that we cannot produce such a superdense matter in our laboratories.