It is predicted that supernovae triggered by stars that do not have enough mass for their cores to form black holes will result in neutron stars.
Neutron stars are small (about 20km across), rotate rapidly and are incredibly dense. They are mostly made of neutrons that formed as electrons combined with protons in the atomic nuclei of the dying stars' collapsing cores. Their powerful magnetic fields lead to radio pulses that can be detected on the Earth each time they rotate. These objects are known as pulsars when the pulses can be detected on the Earth.
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