Neutron stars and the equation of state (original) (raw)

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...

Equation of state of nucleon matter and neutron star structure

Physical Review C, 1998

Properties of dense nucleon matter and the structure of neutron stars are studied using variational chain summation methods and the new Argonne v 18 two-nucleon interaction, which provides an excellent fit to all of the nucleonnucleon scattering data in the Nijmegen data base. The neutron star gravitational mass limit obtained with this interaction is 1.67M ⊙ . Boost corrections to the two-nucleon interaction, which give the leading relativistic effect of order (v/c) 2 , as well as three-nucleon interactions, are also included in the nuclear Hamiltonian. Their successive addition increases the mass limit to 1.80 and 2.20 M ⊙ . Hamiltonians including a three-nucleon interaction predict a transition in neutron star matter to a phase with neutral pion condensation at a baryon number density of ∼ 0.2 fm −3 . Neutron stars predicted by these Hamiltonians have a layer with a thickness on the order of tens of meters, over which the density changes rapidly from that of the normal to the condensed phase. The material in this thin layer is a mixture of the two phases. We also investigate the possibility of dense nucleon matter having an admixture of quark matter, described using the bag model equation of state. Neutron stars of 1.4M ⊙ do not appear to have quark matter admixtures in their cores. However, the heaviest stars are predicted to have cores consisting of a quark and nucleon matter mixture. These admixtures reduce the maximum mass of neutron stars from 2.20 to 2.02 (1.91) M ⊙ for bag constant B = 200 (122) MeV/fm 3 . Stars with pure quark matter in their cores are found to be unstable. We also consider the possibility that matter is maximally incompressible above an assumed density, and show that realistic models of nuclear forces limit the maximum mass of neutron stars to be below 2.5M ⊙ . The effects of the phase transitions on the composition of neutron star matter and its adiabatic index Γ are discussed.

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.

Neutron Star Interiors and the Equation of State of Superdense Matter

Astrophysics and Space Science Library, 2009

Ultra-Dense Neutron Star Matter, Strange Quark Stars, and the Nuclear Equation of State

International Journal of Modern Physics E, 2007

With central densities way above the density of atomic nuclei, neutron stars contain matter in one of the densest forms found in the universe. Depending of the density reached in the cores of neutron stars, they may contain stable phases of exotic matter found nowhere else in space. This article gives a brief overview of the phases of ultradense matter predicted to exist deep inside neutron stars and discusses the equation of state (EoS) associated with such matter.

Neutron stars and the high density equation of state

AIP Conference Proceedings, 2009

One of the key ingredients to understand the properties of neutrons stars 1 (NS) is the equation of state at finite densities far beyond nuclear saturation. Investigating the phase structure of quark matter that might be realized in the core of NS inspires theory and observation. We discuss recent results of our work to point out our view on challenges and possibilities in this evolving field by means of a few examples.

From hadrons to quarks in neutron stars: a review

Reports on progress in physics. Physical Society (Great Britain), 2018

In recent years our understanding of neutron stars has advanced remarkably, thanks to research converging from many directions. The importance of understanding neutron star behavior and structure has been underlined by the recent direct detection of gravitational radiation from merging neutron stars. The clean identification of several heavy neutron stars, of order two solar masses, challenges our current understanding of how dense matter can be sufficiently stiff to support such a mass against gravitational collapse. Programs underway to determine simultaneously the mass and radius of neutron stars will continue to constrain and inform theories of neutron star interiors. At the same time, an emerging understanding in quantum chromodynamics (QCD) of how nuclear matter can evolve into deconfined quark matter at high baryon densities is leading to advances in understanding the equation of state of the matter under the extreme conditions in neutron star interiors. We review here the eq...

Massive quarks in neutron stars

Physics Letters B, 1996

We study various neutron star properties using the Color-Dielectric model to describe quark matter. For the baryon sector at low densities we employ the Walecka model. Applying Gibbs criteria to this composite system, we find that, for matter at r-equilibrium, the pure hadronic phase ends at 0.11 fm -3 and that the mixed quark and hadronic phase extends to 0.31 fm -3. The resulting equation of state yields a maximum nefitron star mass of 1.59M®. A neutron star with total mass of 1.4M® will consist of a crust made of hadronic matter only, a ~ 1 km thick region of mixed phase and a core composed of pure quark matter. Implications for the cooling of neutron stars are discussed.

Quark Matter in Neutron Stars: An Aperçu

Modern Physics Letters A, 2006

The existence of deconfined quark matter in the superdense interior of neutron stars is a key question that has drawn considerable attention over the past few decades. Quark matter can comprise an arbitrary fraction of the star, from 0 for a pure neutron star to 1 for a pure quark star, depending on the equation of state of matter at high density. From an astrophysical viewpoint, these two extreme cases are generally expected to manifest different observational signatures. An intermediate fraction implies a hybrid star, where the interior consists of mixed or homogeneous phases of quark and nuclear matter, depending on surface and Coulomb energy costs, as well as other finite size and screening effects. In this brief review article, we discuss what we can deduce about quark matter in neutron stars in light of recent exciting developments in neutron star observations. We state the theoretical ideas underlying the equation of state of dense quark matter, including color superconducting quark matter. We also highlight recent advances stemming from re-examination of an old paradigm for the surface structure of quark stars and discuss possible evolutionary scenarios from neutron stars to quark stars, with emphasis on astrophysical observations.

Properties of high-density matter in neutron stars

This short review aims at giving a brief overview of the various states of matter that have been suggested to exist in the ultra-dense centers of neutron stars. Particular emphasis is put on the role of quark deconfinement in neutron stars and on the possible existence of compact stars made of absolutely stable strange quark matter (strange stars). Astrophysical phenomena, which distinguish neutron stars from quark stars, are discussed and the question of whether or not quark deconfinement may occur in neutron stars is investigated. Combined with observed astrophysical data, such studies are invaluable to delineate the complex structure of compressed baryonic matter and to put firm constraints on the largely unknown equation of state of such matter.

Neutron stars and the equation of state (original) (raw)

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