Anthea Fantina

Analytical representations of unified equations of state of neutron-star matter

Analytical representations are derived for two equations of state (EOSs) of neutron-star matter: FPS and SLy. Each of these EOSs is unified, that is, it describes the crust and the core of a neutron star using the same physical model. Two versions of the EOS parametrization are considered. In the first one, pressure and mass density are given as functions of the baryon density. In the second version, pressure, mass density, and baryon density are given as functions of the pseudo-enthalpy, which makes this representation particularly useful for 2-D calculations of stationary rotating configurations of neutron stars.

On the Maximum Mass of Neutron Stars

One of the most intriguing questions about neutron stars concerns their maximum mass. The answer is intimately related to the properties of matter at densities far beyond that found in heavy atomic nuclei. The current view on the internal constitution of neutron stars and on their maximum mass, both from theoretical and observational studies, are briefly reviewed.

Masses of neutron stars and nuclei

We calculate the maximum mass of neutron stars for three different equations of state (EOSs) based on generalized Skyrme functionals that are simultaneously fitted to essentially all the 2003 nuclear mass data (the rms deviation is 0.58 MeV in all three cases) and to one or other of three different equations of state of pure neutron matter, each determined by a different many-body calculation using realistic two- and three-body interactions but leading to significantly different degrees of stiffness at the high densities prevailing in neutron-star interiors. The observation of a neutron star with mass 1.97 ± 0.04 M⊙ eliminates the softest of our models (BSk19), but does not discriminate between BSk20 and BSk21. However, nuclear-mass measurements that have been made since our models were constructed strongly favor BSk21, our stiffest functional.

Stability of super-Chandrasekhar magnetic white dwarfs

It has been recently proposed that very massive white dwarfs endowed with strongly quantizing magnetic fields might be the progenitors of overluminous type Ia supernovae like SN 2006gz and SN 2009dc. In this paper, we show that the onset of electron captures and pycnonuclear reactions in these putative super-Chandrasekhar white dwarfs may severely limit their stability.

Giant Pulsar Glitches and the Inertia of Neutron-Star Crusts

Giant pulsar frequency glitches as detected in the emblematic Vela pulsar have long been thought to be the manifestation of a neutron superfluid permeating the inner crust of a neutron star. However, this superfluid has been recently found to be entrained by the crust, and as a consequence it does not carry enough angular momentum to explain giant glitches. The extent to which pulsar-timing observations can be reconciled with the standard vortex-mediated glitch theory is studied considering the current uncertainties on dense-matter properties. To this end, the crustal moment of inertia of glitching pulsars is calculated employing a series of different unified dense-matter equations of state.

Phase transitions in dense matter and the maximum mass of neutron stars

Context. The recent precise measurement of the mass of pulsar PSR J1614−2230, as well as observational indications of even more massive neutron stars, has revived the question of the composition of matter at the high densities prevailing inside neutron-star cores. Aims. We study the impact on the maximum possible neutron-star mass of an “exotic” core consisting of non-nucleonic matter. For this purpose, we study the occurrence of a first-order phase transition in nucleonic matter. Methods. Given the current lack of knowledge of non-nucleonic matter, we consider the stiffest possible equation of state subject only to the constraints of causality and thermodynamic stability. The case of a hadron-quark phase transition is discussed separately. The purely nucleonic matter is described using a set of unified equations of state that have been recently developed to permit a consistent treatment of both homogeneous and inhomogeneous phases. We then compute the mass-radius relation of cold nonaccreting neutron stars with and without exotic cores from the Tolman-Oppenheimer-Volkoff equations. Results. We find that even if there is a significant softening of the equation of state associated with the actual transition to an exotic phase, there can still be a stiffening at higher densities closer to the center of the star that is sufficient to increase the maximum possible mass. However, with quarks the maximum neutron-star mass is always reduced by assuming that the sound speed is limited by c/ √ 3 as suggested by QCD calculations. In particular, by invoking such a phase transition, it becomes possible to support PSR J1614−2230 with a nucleonic equation of state that is soft enough to be compatible with the kaon and pion production in heavy-ion collisions.

Neutron star properties with unified equations of state of dense matter

Aims. In this paper, we study the global properties of neutron stars (NSs), as predicted by the Brussels-Montreal equations of state (EoSs). These EoSs, which provide a unified description of all regions of a NS, are based on the generalised Skyrme functionals BSk19, BSk20, and BSk21 that were simultaneously fitted to almost all the nuclear mass data and constrained to reproduce various properties of infinite nuclear matter, as obtained from microscopic calculations. Methods. We solved Einstein’s equations of general relativity for both non-rotating and rigidly rotating NSs using these unified EoSs. Results. The NS properties thus obtained are compared with various astrophysical observations. We find that only the stiffest EoS, based on the functional BSk21, is compatible with all the constraints inferred from these observations.

Extended equation of state for core-collapse simulations

In stellar core-collapse events matter is heated and compressed to densities above nuclear matter saturation density. For progenitor stars with masses above roughly 25

Symmetry energy: nuclear masses and neutron stars

{M}_{\ensuremath{\bigodot}}

Neutron drip transition in accreting and nonaccreting neutron star crusts

, which eventually form black holes, the temperatures and densities reached during the collapse are so high that a traditional description in terms of electrons, nuclei, and nucleons is no longer adequate. We present here an improved equation of state containing, in addition, pions and hyperons. They become abundant in the high-temperature-and-density regime. We study the different constraints on such an equation of state, coming from both hyperonic data and observations of neutron-star properties. To test the zero-temperature versions of our new equations of state, we perform numerical simulations of the collapse of a neutron star to a black hole. We discuss the influence of the additional particles on the thermodynamic properties within the hot versions of the equation of state and we show that, in regimes relevant to core-collapse and black-hole formation, the effects of pions and hyperons on pressure, internal energy, and sound speed are not negligible.