Strange matter is a form of quark matter, matter that consist primarily of quarks. Strange matter is a 'liquid' made of up, down, and strange quarks, and is different to non-strange quark matter because non-strange quark matter contains only up and down quarks, while strange quark matter has strange quarks as well. Strange matter is thought to exist in the cores of neutron stars. Strange matter only exists at extremely high densities (like in cores of neutron stars). 'Charm matter', quark matter made of charm quarks could be possible, but only at much higher densities.