Quark stars structure

The discovery of the quark structure of matter led to the suggestion of possible existence of quark stars, which are even more compact than neutron stars. In the presence of indefiniteness concerning the quark structure of matter it is not possible now to make definite statements about the existence or nonexistence of stable quark stars, observational and theoretical investigations on this topic are still in progress. 

Aguirre, R. M., De Paoli, A. L. (2002). Neutron star structure in a quark model with excluded volume correction. Phys.Rev.C68 055804. 

NEUTRON STAR STRUCTURE WITH HYPERONS AND QUARKS... 

Neutron Star Structure with Hyperons and Quarks... 

In this contribution we reported the theoretical description of nuclear matter in the BHF approach and its various refinements, with the application to neutron star structure calculation. We pointed out the important role of TBF at high density, which is, however, strongly compensated by the inclusion of hyperons. The resulting hadronic neutron star configurations have maximum masses of only about 1.3 M , and the presence of quark matter inside the star is required in order to reach larger values. 

Keywords Relativistic stars - structure and stability, Quark-gluon plasma, Nuclear physics... 

Figure 15. Left graph Quark star cooling by antineutrino and photon emission from the surface. Middle graph Two-phase structure developes due to the trapped antineutrinos a normal quark matter shell and a superconducting interior. Right graph Antineutrino untrapping and burst-type release of energy.

The final result for the structure of hybrid neutron stars is shown in Fig. 11, displaying mass-radius and mass-central density relations. It is evident that the most striking effect of the inclusion of quark matter is the increase of the maximum mass, now reaching about 1.5 M . At the same time, the typical neutron star radius is reduced by about 3 km to typically 9 km. Hybrid neutron stars are thus more compact than purely hadronic ones and their central energy density is larger. For completeness, the figure shows besides static neutron star... 

Abstract We investigate the phase structure of color superconducting quark matter at intermediate densities for two- and three flavor systems. We thereby focus our attention on the influence of charge neutrality conditions as well as /3-equilibrium on the different phases. These constraints are relevant in the context of quark matter at the interior of compact stars. We analyze the implications of color superconductivity on compact star configurations using different hadronic and quark equations of state. 

Besides the crust and the hadron shell, the hybrid star contains also a quark core. Both the nucleon shell and the quark core can be in superconducting phases, in dependence on the value of the temperature. Fluctuations affect transport coefficients, specific heat, emissivity, masses of low-lying excitations and respectively electromagnetic properties of the star, like electroconductivity and magnetic field structure, e.g., renormalizing critical values of the magnetic field (/ ,, Hc, Hc2). 

As a first step in this direction we will discuss here the two flavor color superconducting (2SC) quark matter phase which occurs at lower baryon densities than the color-flavor-locking (CFL) one, see [18, 32], Studies of three-flavor quark models have revealed a very rich phase structure (see [32] and references therein). However, for applications to compact stars the omission of the strange quark flavor within the class of nonlocal chiral quark models considered here may be justified by the fact that central chemical potentials in stable star configurations do barely reach the threshold value at which the mass gap for strange quarks breaks down and they appear in the system [20], Therefore we will not discuss here first applications to calculate compact star configurations with color superconducting quark matter phases that have employed non-dynamical quark models... 

Since the discovery of the parton substructure of nucleons and its interpretation within the constituent quark model, much effort has been spent to explain the properties of these particles and the structure of high density phases of matter is under current experimental investigation in heavy-ion collisions [17]. While the diagnostics of a phase transition in experiments with heavy-ion beams faces the problems of strong non-equilibrium and finite size, the dense matter in a compact star forms a macroscopic system in thermal and chemical equilibrium for which effects signalling a phase transition shall be most pronounced [8],... 

Fig. 30. Schematic structure of a neutron star, showing core made up of quarks and hyperons inside a degenerate neutron layer inside an iron-rich mantle. Approximate...

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