765 research outputs found
Cooling Evolution of Hybrid Stars
The cooling of compact isolated objects for different values of the
gravitational mass has been simulated for two alternative assumptions. One is
that the interior of the star is purely hadronic and second that the star can
have a rather large quark core. It has been shown that within a nonlocal chiral
quark model the critical density for a phase transition to color
superconducting quark matter under neutron star conditions can be low enough
for these phases to occur in compact star configurations with masses below 1.3
M_sun. For a realistic choice of parameters the equation of state (EoS) allows
for 2SC quark matter with a large quark gap ~ 100 MeV for u and d quarks of two
colors that coexists with normal quark matter within a mixed phase in the
hybrid star interior. We argue that, if in the hadronic phase the neutron
pairing gap in 3P_2 channel is larger than few keV and the phases with unpaired
quarks are allowed, the corresponding hybrid stars would cool too fast.
Even in the case of the essentially suppressed 3P_2 neutron gap if free
quarks occur for M < 1.3 M_sun, as it follows from our EoS, one could not
appropriately describe the neutron star cooling data existing by today.
It is suggested to discuss a "2SC+X" phase, as a possibility to have all
quarks paired in two-flavor quark matter under neutron star constraints, where
the X-gap is of the order of 10 keV - 1 MeV. Density independent gaps do not
allow to fit the cooling data. Only the presence of an X-gap that decreases
with increase of the density could allow to appropriately fit the data in a
similar compact star mass interval to that following from a purely hadronic
model.Comment: 10 pages, 5 figures, Talk given at Joint Meeting
Heidelberg-Liege-Paris-Rostock (HLPR 2004), Spa, Belgium, 16-18 Dec 200
Strangeness in the cores of neutron stars
The measurement of the mass 1.97 +/- 0.04 M_sun for PSR J1614-2230 provides a
new constraint on the equation of state and composition of matter at high
densities. In this contribution we investigate the possibility that the dense
cores of neutron stars could contain strange quarks either in a confined state
(hyperonic matter) or in a deconfined one (strange quark matter) while
fulfilling a set of constraints including the new maximum mass constraint. We
account for the possible appearance of hyperons within an extended version of
the density-dependent relativistic mean-field model, including the phi-meson
interaction channel. Deconfined quark matter is described by the color
superconducting three-flavor NJL model.Comment: 6 pages, 2 figures, contribution to "Strangeness in Quark Matter
2011", Cracow, September 18-24, 201
Effects of quark matter and color superconductivity in compact stars
The equation of state for quark matter is derived for a nonlocal, chiral
quark model within the mean field approximation. We investigate the effects of
a variation of the form factors of the interaction on the phase diagram of
quark matter under the condition of beta-equilibrium and charge neutrality.
Special emphasis is on the occurrence of a diquark condensate which signals a
phase transition to color superconductivity and its effects on the equation of
state. We calculate the quark star configurations by solving the Tolman-
Oppenheimer- Volkoff equations and obtain for the transition from a hot, normal
quark matter core of a protoneutron star to a cool diquark condensed one a
release of binding energy of the order of Delta M c^2 ~ 10^{53} erg. We study
the consequences of antineutrino trapping in hot quark matter for quark star
configurations with possible diquark condensation and discuss the claim that
this energy could serve as an engine for explosive phenomena. A "phase diagram"
for rotating compact stars (angular velocity-baryon mass plane) is suggested as
a heuristic tool for obtaining constraints on the equation of state of QCD at
high densities. It has a critical line dividing hadronic from quark core stars
which is correlated with a local maximum of the moment of inertia and can thus
be subject to experimental verification by observation of the rotational
behavior of accreting compact stars.Comment: 14 pages, 12 figures, Talk given at 2nd International Workshop on
Hadron Physics: Effective Theories of Low-Energy QCD, Coimbra, Portugal,
25-29 Sep 200
Bayesian Analysis for Extracting Properties of the Nuclear Equation of State from Observational Data including Tidal Deformability from GW170817
We develop a Bayesian analysis method for selecting the most probable
equation of state under a set of constraints from compact star physics, which
now include the tidal deformability from GW170817. We apply this method for the
first time to a two-parameter family of hybrid equations of state that is based
on realistic models for the hadronic phase (KVORcut02) and the quark matter
phase (SFM) which produce a third family of hybrid stars in the
mass-radius diagram. One parameter () characterizes the screening of
the string tension in the string-flip model of quark matter while the other
() belongs to the mixed phase construction that mimics the
thermodynamics of pasta phases and includes the Maxwell construction as a
limiting case for . We present the corresponding results for
compact star properties like mass, radius and tidal deformabilities and use
empirical data for them in the newly developed Bayesian analysis method to
obtain the probabilities for the model parameters within their considered
range.Comment: 8 pages, 4 figures, version accepted for publication in univers
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