Quark
Other phases of quark matter

Under sufficiently extreme conditions, quarks may become "deconfined" out of bound states and propagate as thermalized "free" excitations in the larger medium. In the course of asymptotic freedom, the strong interaction becomes weaker at increasing temperatures. Eventually, color confinement would be effectively lost in an extremely hot plasma of freely moving quarks and gluons. This theoretical phase of matter is called quark–gluon plasma.

The exact conditions needed to give rise to this state are unknown and have been the subject of a great deal of speculation and experimentation. An estimate puts the needed temperature at (1.90 ± 0.02) × 10 kelvin. While a state of entirely free quarks and gluons has never been achieved (despite numerous attempts by CERN in the 1980s and 1990s), recent experiments at the Relativistic Heavy Ion Collider have yielded evidence for liquid-like quark matter exhibiting "nearly perfect" fluid motion.

The quark–gluon plasma would be characterized by a great increase in the number of heavier quark pairs in relation to the number of up and down quark pairs. It is believed that in the period prior to 10 seconds after the Big Bang (the quark epoch), the universe was filled with quark–gluon plasma, as the temperature was too high for hadrons to be stable.

Given sufficiently high baryon densities and relatively low temperatures – possibly comparable to those found in neutron stars – quark matter is expected to degenerate into a Fermi liquid of weakly interacting quarks. This liquid would be characterized by a condensation of colored quark Cooper pairs, thereby breaking the local SU(3) symmetry. Because quark Cooper pairs harbor color charge, such a phase of quark matter would be color superconductive; that is, color charge would be able to pass through it with no resistance.
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