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 1.8 times that of Sol, the resulting neutron star typically continued to compress until it became a black hole.[1]
