Observations Of Compact Stars Research Articles

Equation of state at high densities and modern compact star observations

Recently, observations of compact stars have provided new data of high accuracy which put strong constraints on the high-density behaviour of the equation of state of strongly interacting matter otherwise not accessible in terrestrial laboratories. The evidence for neutron stars with high mass (M = 2.1 ± 0.2 M⊙ for PSR J0751 + 1807) and large radii (R > 12 km for RX J1856-3754) rules out soft equations of state and has provoked a debate whether the occurrence of quark matter in compact stars can be excluded as well. In this contribution, it is shown that modern quantum field theoretical approaches to quark matter including colour superconductivity, and a vector meanfield allow a microscopic description of hybrid stars which fulfil the new, strong constraints. The deconfinement transition in the resulting stiff hybrid equation of state is weakly first order so that its signals have to be expected due to specific changes in transport properties governing the rotational and cooling evolution caused by the colour superconductivity of quark matter. A similar conclusion holds for the investigation of quark deconfinement in future generations of nucleus–nucleus collision experiments at low temperatures and high baryon densities such as CBM @ FAIR.

Modern compact star observations and the quark matter equation of state

We present a hybrid equation of state (EoS) for dense matter that satisfies phenomenological constraints from modern compact star (CS) observations which indicate high maximum masses (M∼2M⊙) and large radii (R>12 km). The corresponding isospin symmetric EoS is consistent with flow data analyses of heavy-ion collisions and a deconfinement transition at ∼0.55 fm−3. The quark matter phase is described by a 3-flavor Nambu–Jona-Lasinio model that accounts for scalar diquark condensation and vector meson interactions while the nuclear matter phase is obtained within the Dirac–Brueckner–Hartree–Fock (DBHF) approach using the Bonn-A potential. We demonstrate that both pure neutron stars and neutron stars with quark matter cores are consistent with modern CS observations. Hybrid star configurations with a CFL quark core are unstable within the present model.

Modern compact star observations and the quark matter EoS

A hybrid equation of state (EoS) for dense matter is presented that satisfies phenomenological constraints from modern compact star (CS) observations which indicate high maximum masses ( M ∼ 2 M ⊙ ) and large radii ( R > 12 km ). The corresponding isospin symmetric EoS is consistent with flow data analyses of heavy-ion collisions. The transition from nuclear to two-flavor color superconducting quark matter at n crit ∼ 0.55 fm − 3 is almost a crossover.