Massive and massless modes of the triplet phase of neutron matter (original) (raw)

Neutron star interiors and the equation of state of ultra-dense matter

2006

Neutron stars contain matter in one of the densest forms found in the Universe. This feature, together with the unprecedented progress in observational astrophysics, makes such stars superb astrophysical laboratories for a broad range of exciting physical studies. This paper gives an overview of the phases of dense matter predicted to make their appearance in the cores of neutron stars. Particular emphasis is put on the role of strangeness. Net strangeness is carried by hyperons, K-mesons, H-dibaryons, and strange quark matter, and may leave its mark in the masses, radii, moment of inertia, dragging of local inertial frames, cooling behavior, surface composition, and the spin evolution of neutron stars. These observables play a key role for the exploration of the phase diagram of dense nuclear matter at high baryon number density but low temperature, which is not accessible to relativistic heavy ion collision experiments.

A new state of dense matter in neutron stars with nucleon structure

arXiv: Nuclear Theory, 2019

The existence of stars with a large mass of 2 solar masses means that the equation of state is stiff enough to provide high enough pressure at large central densities. Previous work shows that such a stiff equation of state is possible if the ground state has nucleons as its constituents. We find this to be so in a chiral soliton ( skyrmion ) model for a composite nucleon which has bound state quarks. The strong binding of the quarks in this composite nucleon is plausibly the origin of the nucleon-nucleon hard core. In this model we find a new state of superdense matter at high density which is a 'topological'cubic crystal of overlapping composite nucleons that are solitons with relativistic quark bound states. The quarks are frozen in a filled band of a unique state, which not an eigenstate of spin or isospin but an eigenstate of spin plus isospin, $ \vec S + \vec I = 0$. In this alternative model we find that all neutron stars have no regular `free'quark matter. Neutro...

Low‐Mass Neutron Stars and the Equation of State of Dense Matter

The Astrophysical Journal, 2003

Neutron-star radii provide useful information on the equation of state of neutron rich matter. Particularly interesting is the density dependence of the equation of state (EOS). For example, the softening of the EOS at high density, where the pressure rises slower than anticipated, could signal a transition to an exotic phase. However, extracting the density dependence of the EOS requires measuring the radii of neutron stars for a broad range of masses. A "normal" 1.4M⊙ (M⊙=solar mass) neutron star has a central density of a few times nuclear-matter saturation density (ρ0). In contrast, low mass (≃ 0.5M⊙) neutron stars have central densities near ρ0 so its radius provides information on the EOS at low density. Unfortunately, low-mass stars are rare because they may be hard to form. Instead, a precision measurement of nuclear radii on atomic nuclei may contain similar information. Indeed, we find a strong correlation between the neutron radius of 208 Pb and the radius of a 0.5M⊙ neutron star. Thus, the radius of a 0.5M⊙ neutron star can be inferred from a measurement of the the neutron radius of 208 Pb. Comparing this value to the measured radius of a ≃ 1.4M⊙ neutron star should provide the strongest constraint to date on the density dependence of the equation of state.

Anomalous thermodynamics and phase transitions in neutron star matter

Physical Review C, 2007

The presence of the long-range Coulomb force in dense stellar matter implies that the total charge cannot be associated with a chemical potential, even if it is a conserved quantity. As a consequence, the analytical properties of the partition sum are modified, changing the order of the phase transitions and affecting the possible occurrence of critical behaviours. The peculiar thermodynamic properties of this system can be understood introducing a model hamiltonian where each charge is independently neutralized by a uniform background of opposite charge. Some consequences on the characteristics of mixed-phase structures in neutron star crusts and supernova cores are discussed.

A new class of g-modes in neutron stars

The Astrophysical Journal, 1992

Beca~se. a n~utron star is ~orn hot, its internal composition is close to chemical equilibrium. In the fluid core, thts tmphes_ that _the rat!o of the_ number densities of charged particles (protons and electrons) to neutrons, x ~.ncfnn, ts an mcreasmg function of the mass density. This composition gradient stably stratifies the m~tter glVlng ~ise to a Br~nt-Viiisiilii frequency N ~ (xgj2H) 112 ~ 500 s-1 , where g is the gravitational acceler-atto~, and H ts the denstty scale height. Consequently, a neutron star core provides a cavity that supports gra_vtty modes (g-modes). These g-modes are distinct from those previously identified with the thermal stratifi-catiOn of the surface layers and t~e chemical stratification of the crust. We compute the lowest-order, quadrupolar, g-modes for cold, Newtoman, neutron star models with M/M 0 = 0.581 and M/M 0 = 1.405 and show that t~e crustal and core g-modes have similar periods. We also discuss damping mechanisms and estimate ~ampmg ~at~s for the core g-modes. Particular attention is paid to damping due to the emission of gravitational radtatwn.

The Equation of State of Nuclear Matter and Neutron Stars Properties

Journal of Modern Physics, 2014

The equation of state (EOS) of symmetric nuclear and pure neutron matter has been investigated extensively by adopting the non-relativistic Brueckner-Hartree-Fock (BHF). For more comparison, the extended BHF approaches using the self-consistent Green's function approach or by including a three-body force will be done. The EOS will be studied for different approaches at zero temperature. We can calculate the total mass and radius of neutron stars using various equations of state. A comparison with relativistic BHF calculations will be done. Relativistic effects are known to be important at high densities, giving an increased repulsion. This leads to a stiffer EOS compared to the EOS derived with a non-relativistic approach.

Minimal Cooling of Neutron Stars: A New Paradigm

The Astrophysical Journal Supplement Series, 2004

A new classification of neutron star cooling scenarios, involving either "minimal" cooling or "enhanced" cooling is proposed. The minimal cooling scenario replaces and extends the so-called standard cooling scenario to include neutrino emission from the Cooper pair breaking and formation process. This emission dominates that due to the modified Urca process for temperatures close to the critical temperature for superfluid pairing. Minimal cooling is distinguished from enhanced cooling by the absence of neutrino emission from any direct Urca process, due either to nucleons or to exotica such as hyperons, Bose condensates or deconfined quarks. Within the minimal cooling scenario, theoretical cooling models can be considered to be a four parameter family involving the equation of state (including various compositional possibilities) of dense matter, superfluid properties of dense matter, the composition of the neutron star envelope, and the mass of the neutron star. The consequences of minimal cooling are explored through extensive variations of these parameters. The results are compared with the inferred properties of thermally-emitting neutron stars in order to ascertain if enhanced cooling occurs in any of them.

Dense Stellar Matter and Structure of Neutron Stars

Eprint Arxiv Astro Ph 9609074, 1996

After giving an overview of the history and idea of neutron stars, I shall discuss, in part one of my lectures, the physics of dense neutron star matter. In this connection concepts like chemical equilibrium and electric charge neutrality will be outlined, and the baryonic and mesonic degrees of freedom of neutron star matter as well as the transition of confined hadronic matter into quark matter at supernuclear densities are studied. Special emphasis is put onto the possible absolute stability of strange quark matter. Finally models for the equation of state of dense neutron star matter, which account for various physical possibilities concerning the unknown behavior of superdense neutron star matter, will be derived in the framework of relativistic nuclear field theory. Part two of my lectures deals with the construction of models of static as well as rapidly rotating neutron stars and an investigation of the cooling behavior of such objects. Both is performed in the framework of Einstein's theory of general relativity. For this purpose the broad collection of models for the equation of state, derived in part one, will be used as an input. Finally, in part three a comparison of the theoretically computed neutron star properties (e.g., masses, radii, moments of inertia, red and blueshifts, limiting rotational periods, cooling behavior) with the body of observed data will be performed. From this conclusions about the interior structure of neutron stars-and thus the behavior of matter at extreme densities-will be drawn.

Nuclear equation of state at high density and the properties of neutron stars

Physical Review C, 2000

We discuss the relativistic nuclear equation of state (EOS) using a relativistic transport model in heavy-ion collisions. From the baryon flow for Au + Au systems at SIS to AGS energies and above we find that the strength of the vector potential has to be reduced moderately at high density or at high relative momenta to describe the flow data at 1-10 A GeV. We use the same dynamical model to calculate the nuclear EOS and then employ this to calculate the gross structure of the neutron star considering the core to be composed of neutrons with an admixture of protons, electrons, muons, sigmas and lambdas at zero temperature. We then discuss these gross properties of neutron stars such as maximum mass and radius in contrast to the observational values.