The central remains of a star which has undergone a
supernova explosion. A neutron star is composed of
baryon degenerate matter (that is electrons have been compressed under huge gravitational forces into protons and produced neutrons) and, hence, has a very high
density . A neutron star has a typical radius of just 10 kilometers but a density of up to 1018 kg/m3. Neutron stars were once thought to be observationally impossible to detect but it seems that the celestial objects known as
pulsars , are nothing more than spinning neutron stars. Also, x-ray bursters are now thought to be binary star systems in which one of the components is a neutron star. The mechanism for outburst is the same as in a traditional
nova except that, instead of the accretion taking place onto a
white dwarf , it spirals down onto a neutron star.