Color Confinement in Dense Regions?

[metastable]

Is the phenomenon of color confinement thought to persist in spatial regions of extreme density, such as the cores and regions surrounding massive stars during supernova, the accretion disks around active galactic nuclei, neutron stars, magnetars, and dense regions of space shortly after the big bang?

 

[vanhees71]

Indeed for very dense and/or hot strongly interacting matter there is convincing evidence from heavy-ion collisions at RHIC and LHC that a socalled quark-gluon plasma is formed, which is a state of matter where quark-gluon degrees of freedom are the relevant degrees of freedom in the many-body system. In the beginning of this field of reseach one has thought that this is a state described as an ideal gas of nearly massless (light) quarks and gluons, but more then 30 years later we've come to the conclusion that in fact we deal with a strongly coupled liquid of quark-gluon like quasiparticles rather than an ideal gas. The evidence of this is both theoretical (through thermal lattice QCD) and observations in heavy-ion collisions. One prime finding is that the produced hadrons' (and we can only measure hadrons, leptons, and photons never single quarks and gluons!) momentum distributions can be explained by the assumption that they originate from a collectively moving hot fireball well described by relativistic hydrodynamics which is nearly ideal (i.e., the viscosity over entropy-density ratio is estimated to be among the lowest values of all known fluids so far). Since this fireball lives for only a few $10 \text{fm}/c$ ($10^{-23} \; \text{s}$) this implies that after the collision the created medium comes within an amazingly short time scale of less than $1 \text{fm}/c$ into this hydrodynamic state close to local thermal equilibrium showing the strong coupling of the fluid.

Whether or not there's such a quark-gluon-plasma state also in the core of neutron stars, is still not so clear. I think there's pretty much a chance to figure this out in more detail since we have now the gravitational-wave astronomy at hand, where we can study the gravitational-wave signals from neutron-star mergers and compare it from predictions of corresponding calculations, which need the equation of state of strongly interacting matter as input. The equation of state is sensitive for the specific gravitational-wave signals in such a collision and also can give hints about the microscpic constituents of the medium. So there's a lot to be expected in the near future!