Hyperon stars in the Brueckner-Bethe-Goldstone theory

Abstract

In the framework of the Brueckner-Bethe-Goldstone theory, we determine a fully microscopic equation of state for asymmetric and $\beta$-stable nuclear matter containing $\sim$ and $\la$ hyperons. We use the Paris and the new Argonne $Av_{18}$ two-body nucleon interaction, whereas the nucleon-hyperon interaction is described by the Njimegen soft-core model. We stress the role played by the three-body nucleon interaction, which produces a strong repulsion at high densities. This enhances enormously the hyperon population, and produces a strong softening of the equation of state, which turns out almost independent on the nucleon-nucleon interaction. We use the new equation of state in order to calculate the structure of static neutron stars. We obtain a maximum mass configuration with $M_{\rm max}$ = 1.26 (1.22) when the Paris ($Av_{18}$) nucleon potential is adopted. Central densities are about 10 times normal nuclear matter density. Stellar rotations, treated within a perturbative approach, increase the value of the limiting mass by about 12%.Comment: 16 pages, latex, 10 figures, submitted to Phys. Rev.

The maximum and minimum mass of protoneutron stars in the Brueckner theory

“…2 for both SNM and PNM. It turns out that the dependence of the free energy on the proton fraction can be approximated very well by a quadratic dependence, as at zero temperature (Bombaci & Lombardo 1991;Baldo et al 1998Baldo et al , 2000a:…”

Phase transition toward strange matter

“…Concerning hyperons, simple energetic considerations suggest that they should be present at high density [10]. However, in the standard picture the opening of hyperon degrees of freedom leads to a considerable softening of the equation of state [10][11][12][13][14][15][16][17], which in turns leads to maximum neutron star masses smaller than the highest values obtained in recent observations [18]. This puzzling situation implies that the hyperon-hyperon and hyperon-nucleon couplings must be much more repulsive at high density than presently assumed [19][20][21][22][23][24][25], and/or that something is missing in the present modelization.…”

“…[30,31]) are scarce. This lack of experimental information induces large uncertainties within the microscopic approaches [11][12][13], which suffer in addition probably from theoretical shortcomings, among others due to the unknown hyperonic threebody forces [32]. Phenomenological extrapolations of the low-density behavior within mean field models are subject to large uncertainties, too.…”

Microscopic study of neutrino trapping in hyperon stars

“…Since then the structrural properties of these hyperon stars have been studied by many researchers using a variety of aproaches (see e.g., Pandharipande 1971;Glendenning 1985;Keil & Janka 1994;Shaffner & Mishustin 1996;Prakash et al 1997;Balberg & Gal 1997;Baldo et al 2000;Vidaña et al 2000a).…”