neutron star
From Trekipedia
A neutron star was a dense core of a star that remained after the star exploded in a supernova. Neutron stars were typically ten to fifteen kilometers in diameter. Within a neutron star, atoms were compressed to such a great degree that the positively-charged protons and negatively-charged electrons were crushed together, with their electrical charges canceling each other out and forming electrically-neutral particles called neutrons. This material is also known as neutronium. If the original mass of the star prior to the supernova was more than 8 times that of Sol, the resulting neutron star typically continued to compress until it became a black hole.[1]
