Quark-star is hypothetically celestial object that is intermediate in density between a neutron star and black hole, as the remnant of a massive neutron star that has collapsed with gravitational pressure sufficient to reduce all constituent particles to strange quarks. Quark-star can be smallest than 11 kilometers diameter. Like neutron stars, quark star are composed of neutrons that have undergone enough pressure by the collapse of the star to have lost their differentiation and disolved into a mass of quarks and gluons. The up and down quarks of which neutrons are composed than change into strange quarks, with the resulting strange mattery compacting into an even denser mass than a neutron star.