Pulsar Signal of Deconfinement

A solitary millisecond pulsar, if near the mass limit, and undergoing a phase transition, either first or second order, provided the transition is to a substantially more compressible phase, will emit a blatantly obvious signal---spontaneous spin-up. Normally a pulsar spins down by angular momentum loss to radiation. The signal is trivial to detect and is estimated to be ``on'' for 1/50 of the spin-down era of millisecond pulsars. Presently about 25 solitary millisecond pulsars are known. The phenomenon is analogous to ``backbending'' observed in high spin nuclei in the 1970's.Comment: 12 pages, 11 figures, Latex-espcrc1.sty (Dec. 1997, Plenary Talk to appear in Nuclear Physics A in the Proceedings of Quark Matter97, Tsukuba, Japan

Strangeness in Compact Stars and Signal of Deconfinement

Phase transitions in compact stars are discussed including hyperonization, deconfinement and crystalline phases. Reasons why kaon condensation is unlikely is reviewed. Particular emphasis is placed on the evolution of internal structure with spin-down of pulsars. A signature of a first order phase transition in the timing structure of pulsars which is strong and easy to measure, is identified.Comment: 17 pages, 15 figures, Latex. (Invited Talk at the International Symposium on ``Strangeness In Quark Matter 1997'', Thera (Santorini), Hellas, April 14-18, 1997, To be published in Journal of Physics G (Organizers: A Panagiotou and J. Madsen

Mapping Deconfinement with a Compact Star Phase Diagram

We have found correlations between properties of the equation of state for stellar matter with a phase transition at supernuclear densities and two characteristic features of a "phase diagram" for rotating compact stars in the angular velocity - baryon number plane: 1) the critical dividing line between mono- and two-phase star configurations and 2) the maximum mass line. The second line corresponds to the minimum mass function for black hole candidates whereas the first one is observable by a population statistics, e.g. for Z-sources in low-mass X-ray binaries. The observation of a population gap in the mass distribution for the latter is suggested as an astrophysical verification of the existence of a first order phase transition in QCD at high densities such as the deconfinement.Comment: 4 pages, 2 figures, Contribution to Proceedings of Quark Matter 2002, Nantes, July 18 - 24, 200

Surface Tension between Kaon Condensate and Normal Nuclear Matter Phase

We calculate for the first time the surface tension and curvature coefficient of a first order phase transition between two possible phases of cold nuclear matter, a normal nuclear matter phase in equilibrium with a kaon condensed phase, at densities a few times the saturation density. We find the surface tension is proportional to the difference in energy density between the two phases squared. Furthermore, we show the consequences for the geometrical structures of the mixed phase region in a neutron star.Comment: 7 pages, 5 figures (Latex

From Quark Stars to Hybrid Stars

We show the possible existence of compact stars having a surface composed of a mixed phase of quarks and hadrons. This scenario can be realized both for self-bound stars, satisfying the so-called Witten-Bodmer hypothesis, and for gravitationally bound stars. This class of solutions of the Tolman-Oppenheimer-Volkoff equation can be obtained in all the models we discuss, within a physically acceptable range of values of the model parameters.Comment: 10 pages, 4 figures, 1 tabl

Spin-up of the hyperon-softened accreting neutron stars

We study the spin-up of the accreting neutron stars with a realistic hyperon-softened equation of state. Using precise 2-D calculations we study the evolutionary tracks of accreting neutron stars in the angular-momentum - frequency plane. In contrast to the case of spinning-down solitary radio-pulsars, where a strong back-bending behavior has been observed, we do not see back-bending phenomenon in the accretion-powered spinning-up case. We conclude that in the case of accretion-driven spin-up the back-bending is strongly suppressed by the mass-increase effect accompanying the angular-momentum increase.Comment: 5 pages, 5 figures, accepted by Astronomy & Astrophysic

Kaon Condensation in Neutron Star Matter with Hyperons

Based on the Kaplan-Nelson Lagrangian, we investigate kaon condensation in dense neutron star matter allowing for the explicit presence of hyperons. Using various models we find that the condensate threshold is sensitive to the behavior of the scalar density; the more rapidly it increases with baryon density, the lower is the threshold for condensation. The presence of hyperons, particularly the $\Sigma^-$, shifts the threshold for $K^-$ condensation to a higher density. In the mean field approach, with hyperons, the condensate amplitude grows sufficiently rapidly that the nucleon effective mass vanishes at a finite density and a satisfactory treatment of the thermodynamics cannot be achieved. Thus, calculations of kaon-baryon interactions beyond the mean field level appear to be necessary.Comment: 13 pages, latex, 3 figures by fax/mail from [email protected]