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We use covariant density functional theory to obtain the equation of state (EoS) of matter in compact stars at non-zero temperature, including the full baryon octet as well as the $Delta(1232)$ resonance states. Global properties of hot $Delta$-admixed hypernuclear stars are computed for fixed values of entropy per baryon ($S/A$) and lepton fraction ($Y_L$). Universal relations between the moment of inertia, quadrupole moment, tidal deformability, and compactness of compact stars are established for fixed values of $S/A$ and $Y_L$ that are analogous to those known for cold catalyzed compact stars. We also verify that the $I$-Love-$Q$ relations hold at finite temperature for constant values of $S/A$ and $Y_L$.
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We study the properties of hot beta-stable nuclear matter using equations of state derived within the Brueckner-Hartree-Fock approach at finite temperature including consistent three-body forces. Simple and accurate parametrizations of the finite-temperature equations of state are provided. The properties of hot neutron stars are then investigated within this framework, in particular the temperature dependence of the maximum mass. We find very small temperature effects and analyze the interplay of the different contributions.
In the first part of this paper, we investigate the possible existence of a structured hadron-quark mixed phase in the cores of neutron stars. This phase, referred to as the hadron-quark pasta phase, consists of spherical blob, rod, and slab rare phase geometries. Particular emphasis is given to modeling the size othis phase in rotating neutron stars. We use the relativistic mean-field theory to model hadronic matter and the non-local three-flavor Nambu-Jona-Lasinio model to describe quark matter. Based on these models, the hadron-quark pasta phase exists only in very massive neutron stars, whose rotational frequencies are less than around 300 Hz. All other stars are not dense enough to trigger quark deconfinement in their cores. Part two of the paper deals with the quark-hadron composition of hot (proto) neutron star matter. To this end we use a local three-flavor Polyakov-Nambu-Jona-Lasinio model which includes the t Hooft (quark flavor mixing) term. It is found that this term leads to non-negligible changes in the particle composition of (proto) neutron stars made of hadron-quark matter.
We model the cooling of hybrid neutron stars combining a microscopic nuclear equation of state in the Brueckner-Hartree-Fock approach with different quark models. We then analyze the neutron star cooling curves predicted by the different models and single out the preferred ones. We find that the possibility of neutron p-wave pairing can be excluded in our scenario.
Using relativistic mean-field models, the formation of clusterized matter, as the one expected to exist in the inner crust of neutron stars, is determined under the effect of strong magnetic fields. As already predicted from a calculation of the unstable modes resulting from density fluctuations at subsaturation densities, we confirm in the present work that for magnetic field intensities of the order of $approx 5 times 10^{16}$ G to $5 times 10^{17}$ G, pasta phases may occur for densities well above the zero-field crust-core transition density. This confirms that the extension of the crust may be larger than expected. It is also verified that the equilibrium structure of the clusterized matter is very sensitive to the intensity of the magnetic fields. As a result, the decay of the magnetic field may give rise to internal stresses which may result on the yield and fracture of the inner crust lattice.
Neutron tunneling between neutron-rich nuclei in inhomogeneous dense matter encountered in neutron star crusts can release enormous energy on a short-timescale to power explosive phenomena in neutron stars. In this work we clarify aspects of this process that can occur in the outer regions of neutron stars when oscillations or cataclysmic events increase the ambient density. We use a time-dependent Hartree-Fock-Bogoliubov formalism to determine the rate of neutron diffusion and find that large amounts of energy can be released rapidly. The role of nuclear binding, the two-body interaction and pairing, on the neutron diffusion times is investigated. We consider a one-dimensional quantum diffusion model and extend our analysis to study the impact of diffusion in three-dimensions. We find that these novel neutron transfer reactions can generate energy at the amount of $simeq 10^{40}-10^{44}$ ergs under suitable conditions.
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