State of matter where protons and neutrons dissolve into a sea of quarks.Quark matter is a state of matter in which protons and neutrons — the particles that make up atomic nuclei — dissolve into their constituent quarks. Under normal conditions, quarks are permanently confined inside hadrons by the strong force, but at extremely high temperatures or densities, this confinement breaks down. The result is a dense, interacting sea of quarks and gluons, often called quark-gluon plasma.
The concept of quark deconfinement was proposed in the 1970s, with early theoretical work by John Collins and Malcolm Perry (1975) and independently by others, suggesting that at sufficiently high density, matter might exist as a quark gas. The term 'quark-gluon plasma' was coined later, and experimental searches began in the 1980s.
At ordinary energies, the strong force binds quarks into triplets (baryons like protons and neutrons) or pairs (mesons). When energy density exceeds a critical threshold — roughly a few hundred MeV per cubic femtometer — the vacuum itself changes, and quarks become deconfined. This transition is analogous to the melting of a solid into a liquid: the hadrons 'melt' into a plasma of their constituents.
Quark matter is studied in heavy-ion colliders like the LHC and RHIC, where gold or lead nuclei are smashed together to recreate conditions from the early universe, helping physicists understand the strong force and the evolution of the cosmos.
Neutron stars may have cores made of quark matter, making them the densest observable objects in the universe.
