Quark matter, also known as quark-gluon plasma (QGP), is a state of matter that is believed to exist at extremely high temperatures and densities. It is characterized by the deconfinement and free movement of quarks and gluons, which are the fundamental constituents of matter and the particles that mediate the strong nuclear force.
The density of quark matter can vary depending on the specific conditions under which it is formed. In heavy-ion collision experiments, where high-energy nuclei are collided, quark-gluon plasma is created for a very short duration. During this time, the matter reaches extremely high energy densities, on the order of several times the normal nuclear density.
To give you a sense of scale, the nuclear density is approximately 2.3 x 10^17 kilograms per cubic meter. In comparison, the densities of quark matter in heavy-ion collisions can reach values of around 10^15 to 10^17 kilograms per cubic meter, which is several orders of magnitude higher than normal nuclear density.
It's worth noting that quark matter is also hypothesized to exist in the cores of neutron stars, where the extreme gravitational pressure compresses matter to extraordinary densities. The precise density of quark matter in neutron stars is still a topic of active research and is highly dependent on the equation of state, which describes the relationship between the pressure and density of the matter. However, it is generally believed that the densities in the core of a neutron star could be several times greater than normal nuclear density, potentially reaching values of 10^17 to 10^18 kilograms per cubic meter or even higher.
It's important to keep in mind that the study of quark matter and its properties is an active field of research, and our understanding of it continues to evolve.