The recent observation of the pulsar PSR J1614-2230 with a mass of 1.97 +/- 0.04 M_sun gives a strong constraint on the quark and nuclear matter equations of state (EoS). We explore the parameter ranges for a parameterized EoS for quark stars. We find that strange stars, made of absolutely stable strange quark matter, comply with the new constraint only if effects from the strong coupling constant and color-superconductivity are taken into account. Hybrid stars, compact stars with a quark matter core and an hadronic outer layer, can be as massive as 2 M_sun, but only for a significantly limited range of parameters. We demonstrate that the appearance of quark matter in massive stars depends crucially on the stiffness of the nuclear matter EoS. We show that the masses of hybrid stars stay below the ones of hadronic and pure quark stars, due to the softening of the EoS at the quark-hadron phase transition.
The appearance of quark matter in the centers of compact stars has a number of astrophysical implications. In this contribution I discuss the structure and stability of compact stars, gravitational radiation from non-axisymmetric deformations, and nucleation and dynamics of vortices (flux tubes) in the color superconducting phases.
High massive compact stars have been reported recently in the literature, providing strong constraints on the properties of the ultradense matter beyond the saturation nuclear density. In view of these results, the calculations of quark star or hybrid star equilibrium structure must be compatible with the provided observational data. But, since the used equations of state describing quark matter are in general too soft, in comparison with the equation of states used to describe the hadronic or nuclear matter, the calculated quark star models presented in the literature are in general not suita…
The theory governing the strong nuclear force, Quantum Chromodynamics, predicts that at sufficiently high energy densities hadronic nuclear matter undergoes a deconfinement transition to a new phase of quarks and gluons. Although this has been observed in ultrarelativistic heavy-ion collisions, it is currently an open question whether quark matter exists inside neutron stars. By combining astrophysical observations and theoretical ab-initio calculations in a model-independent way, we find that the inferred properties of matter in the cores of neutron stars with mass corresponding to 1.4 solar …
Rapidly Spinning Massive Pulsars as an Indicator of Quark Deconfinement
Universidade de Lisboa（里斯本大学）；University of Coimbra（科英布拉大学）；University of Wroclaw（弗罗茨瓦夫大学）；University of Southampton（南安普顿大学）；Helmholtz-Zentrum Dresden-Rossendorf (HZDR)（德累斯顿-罗斯多夫亥姆霍兹中心）；Center for Advanced Systems Understanding (CASUS)（先进系统理解中心）
On the basis of the percolation picture from the hadronic phase with hyperons to the quark phase with strangeness, we construct a new equation of state (EOS) with the pressure interpolated as a function of the baryon density. The maximum mass of neutron stars can exceed $2M_{\odot}$ if the following two conditions are satisfied; (i) the crossover from the hadronic matter to the quark matter takes place at around three times the normal nuclear matter density, and (ii) the quark matter is strongly interacting in the crossover region and has stiff equation of state. This is in contrast to the con…
Using the idea of a smooth crossover from the hadronic matter with hyperons to quark matter with strangeness, we show that the maximum mass of neutron stars with quark matter core can be larger than those without quark matter core. This is in contrast to the conventional softening of equation of state due to exotic components at high density. Essential conditions to reach our conclusion are (i) the crossover takes place at relatively low densities, around 3 times the normal nuclear density, and (ii) the quark matter is strongly interacting in the crossover region. By these, the pressure of the…
The structured hadron-quark mixed phase, known as the pasta phase, is expected to appear in the core of massive neutron stars. Motivated by the recent advances in astrophysical observations, we explore the possibility of the appearance of quarks inside neutron stars and check its compatibility with current constraints. We investigate the properties of the hadron-quark pasta phases and their influences on the equation of state (EOS) for neutron stars. In this work, we extend the energy minimization (EM) method to describe the hadron-quark pasta phase, where the surface and Coulomb contributions…
We study the impact of a hadron-quark phase transition on the maximum neutron-star mass. The hadronic part of the equation of state relies on the most up-to-date Skyrme nuclear energy density functionals, fitted to essentially all experimental nuclear mass data and constrained to reproduce the properties of infinite nuclear matter as obtained from microscopic calculations using realistic forces. We show that the softening of the dense matter equation of state due to the phase transition is not necessarily incompatible with the existence of massive neutron stars like PSR J1614-2230.
Phenomenological Scaling Relations for SQM Stars with a Massive s-Quark in Gravitationally Strong Magnetic Fields under the Spherical Symmetry Approximation
Quark clustering could occur in cold quark matter because of the strong coupling between quarks at realistic baryon densities of compact stars. Although one may still not be able to calculate this conjectured matter from first principles, the inter-cluster interaction might be analogized to the interaction between inert molecules. Cold quark matter would then crystallize in a solid state if the inter-cluster potential is deep enough to trap the clusters in the wells. We apply the Lennard-Jones potential to describe the inter-cluster potential, and derive the equations of state, which are stiff…
We estimate the critical magnetic field strength at which the lowest or second Landau levels play an important role in the quark phase inside the hybrid stars, and show that the magnetic field should be in the order of $10^{19}$ Gauss at the nuclear density $\sim0.16$ fm$^{-3}$. We also find that the pressure of quark matter settling only in the lowest Landau level can be expressed as a function of the energy density independently of the magnetic field strength, which corresponds to the causality limit of a stiff equation of state. Adiabatic index of quark matter well exceeds 4/3 in the core, …
We review some recent results about the mechanism of deconfinement of hadronic matter into quark matter in cold neutron stars and protoneutron stars. We discuss the role of finite size effects and the relevance of temperature and density fluctuations on the nucleation process. We also examine the importance of surface effects for mixed phases in hybrid stars. A small drop of quark matter nucleated at the core of a compact star may grow if the conversion is sufficiently exothermic. In such a case, it may trigger the burning of the stellar core and even the whole star if quark matter is absolute…
Massive neutron stars may harbor deconfined quark matter in their cores. I review some recent work on the microphysics and the phenomenology of compact stars with cores made of quark matter. This includes the equilibrium and stability of non-rotating and rapidly rotating stars, gravitational radiation from deformations in their quark cores, neutrino radiation and dichotomy of fast and slow cooling, and pulsar radio-timing anomalies.
We explore the possibility of three phases in the core of neutron star in a form of triple layers. From the center, strange quark matter, kaon condensed nuclear matter and nuclear matter form a triple layer. We discuss how the phase of strange quark matter is smoothly connected to kaon condensed nuclear matter phase. We also demonstrate that the compact star with triple layered structure can be a model compatible with the 1.97-solar-mass object PSR J1614-2230 recently observed.
We examine the thermal evolution of a sequence of compact objects containing low-mass hadronic and high-mass quark-hadronic stars constructed from a microscopically motivated equation of state. The dependence of the cooling tracks in the temperature versus age plane is studied on the variations of the gaplessness parameter (the ratio of the pairing gap for red-green quarks to the electron chemical potential) and the magnitude of blue quark gap. The pairing in the red-green channel is modeled assuming an inhomogeneous superconducting phase to avoid tachionic instabilities and anomalies in the s…
LSQ14bdq and SN 2006oz are super-luminous, hydrogen-poor, SNe with double-humped light curves. We show that a Quark-Nova (QN; explosive transition of the neutron star to a quark star) occurring in a massive binary, experiencing two Common Envelope (CE) phases, can quantitatively explain the light curves of LSQ14bdq and SN 2006oz. The more massive component (A) explodes first as a normal SN, yielding a Neutron Star which ejects the hydrogen envelope of the companion when the system enters its first CE phase. During the second CE phase, the NS spirals into and inflates the second He-rich CE. In …
We study the tidal deformability of bare quark stars and hybrid compact stars composed of a quark matter core in general relativity, assuming that the deconfined quark matter exists in a crystalline color superconducting phase. We find that taking the elastic property of crystalline quark matter into account in the calculation of the tidal deformability can break the universal I-Love relation discovered for fluid compact stars, which connects the moment of inertia and tidal deformability. Our result suggests that measurements of the moment of inertia and tidal deformability can in principle be…
Quark-novae leave behind quark stars with a surrounding metal-rich fall-back (ring-like) material. These compact remnants have high magnetic fields and are misconstrued as magnetars; however, several observational features allow us to distinguish a quark star (left behind by a quark-nova) from a neutron star with high magnetic field. In our model, bursting activity is expected from intermittent accretion events from the surrounding fall-back debris leading to X-ray bursts (in the case of a Keplerian ring) or gamma ray bursts (in the case of a co-rotating shell). The details of the spectra are …
We show a scenario for the cooling of compact stars considering the central source of Cassiopeia A (Cas A). The Cas A observation shows that the central source is a compact star with high effective temperature, and it is consistent with the cooling without exotic phases. The Cas A observation also gives the mass range of $M \geq 1.5 M_\odot$. It may conflict with the current cooling scenarios of compact stars that heavy stars show rapid cooling. We include the effect of the color superconducting (CSC) quark matter phase on the thermal evolution of compact stars. We assume the gap energy of CSC…
