neutron star

Final stage of massive stars that explode as a supernova. In the explosion process, the core of the star collapses to form a compact object with roughly 1.4 solar masses that mostly consists of nuclear matter, predominantly of neutrons.

For astronomers, neutron stars are of interest as there exists a variety called pulsars from which they receive highly regular pulses of electromagnetic radiation. For relativists, they are interesting as the typical effects of general relativity are very pronounced in objects that compact (compare PSR 1913+16, double pulsar PSR J0737-3029A/B).