Neutron star
A neutron star is the collapsed core of an extremely large star, where gravitational forces eliminate virtually all of the space inside the star's nuclei, crushing protons and electrons together and turning them into neutrons. It is estimated that one cubic metre of the matter from the centre of a neutron star could have a mass of up to 10^18 kilograms, or a million billion tonnes. A neutron star of more than three solar masses collapses further into a black hole which can make some of those the densest objects
