655 research outputs found
Quark matter in compact stars: astrophysical implications and possible signatures
After a brief non technical introduction of the basic properties of strange
quark matter (SQM) in compact stars, we consider some of the late important
advances in the field, and discuss some recent astrophysical observational data
that could shed new light on the possible presence of SQM in compact stars. We
show that above a threshold value of the gravitational mass a neutron star
(pure hadronic star) is metastable to the decay (conversion) to an hybrid
neutron star or to a strange star. We explore the consequences of the
metastability of "massive" neutron stars and of the existence of stable compact
"quark" stars (hybrid neutron stars or strange stars) on the concept of
limiting mass of compact stars, and we give an extension of this concept with
respect to the "classical" one given in 1939 by Oppenheimer and Volkoff.Comment: Invited talk at "the Eleventh Marcel Grossman Meeting on General
Relativity", Berlin 200
Neutron star properties from optimized chiral nuclear interactions
We adopt two- and three-body nuclear forces derived at the
next-to-next-to-leading-order (N2LO) in the framework of effective chiral
perturbation theory (ChPT) to calculate the equation of state (EOS) of
-stable neutron star matter using the Brueckner--Hartree--Fock many-body
approach. We use the recent optimized chiral two-body nuclear interaction at
N2LO derived by \cite{ekstrom1} and two different parametrizations of the
three-body N2LO interaction: the first one is fixed to reproduce the saturation
point of symmetric nuclear matter while the second one is fixed to reproduce
the binding energies of light atomic nuclei. We show that in the second case
the properties of nuclear matter are not well determined whereas in the first
case various empirical nuclear matter properties around the saturation density
are well reproduced. We also calculate the nuclear symmetry energy as
a function of the nucleonic density and compare our results with the empirical
constraints obtained using the excitation energies of isobaric analog states in
nuclei and the experimental data on the neutron skin thickness of heavy nuclei.
We next calculate various neutron star properties and in particular the
mass-radius and mass-central density relations. We find that the adopted
interactions based on a fully microscopic framework, are able to provide an EOS
which is consistent with the present data of measured neutron star masses and
in particular with the mass of the neutron star in PSR
J0348+0432. We finally consider the possible presence of hyperons in the
stellar core and we find a softening of the EOS and a substantial reduction of
the stellar maximum mass in agreement with similar calculations present in the
literature.Comment: Accepted for publication in PAS
A link between measured neutron star masses and lattice QCD data
We study the hadron-quark phase transition in neutron star matter and the
structural properties of hybrid stars using an equation of state (EOS) for the
quark phase derived with the field correlator method (FCM). We make use of the
measured neutron star masses, and particularly the mass of PSR J1614-2230, to
constrain the values of the gluon condensate which is one of the EOS
parameter within the FCM. We find that the values of extracted from the
mass measurement of PSR J1614-2230 are fully consistent with the values of the
same quantity derived, within the FCM, from recent lattice quantum
chromodynamics (QCD) calculations of the deconfinement transition temperature
at zero baryon chemical potential. The FCM thus provides a powerful tool to
link numerical calculations of QCD on a space-time lattice with neutron stars
physics.Comment: Minor changes and typos correcte
Quark deconfinement and neutrino trapping in compact stars
We study the role played by neutrino trapping on the hadron star (HS) to
quark star (QS) conversion mechanism proposed recently by Berezhiani and
collaborators. We find that the nucleation of quark matter drops inside hadron
matter, and therefore the conversion of a HS into a QS, is strongly inhibit by
the presence of neutrinos.Comment: 3 pages, 3 figures. Talk given at the VIII International Conference
on Strangeness in Quark Matter. Cape Town, South Africa, Septembre 200
Quark matter nucleation in hot hadronic matter
We study the quark deconfinement phase transition in hot -stable
hadronic matter. Assuming a first order phase transition, we calculate the
enthalpy per baryon of the hadron-quark phase transition. We calculate and
compare the nucleation rate and the nucleation time due to thermal and quantum
nucleation mechanisms. We compute the crossover temperature above which thermal
nucleation dominates the finite temperature quantum nucleation mechanism. We
next discuss the consequences for the physics of proto-neutron stars. We
introduce the concept of limiting conversion temperature and critical mass
for proto-hadronic stars, and we show that proto-hadronic stars with a
mass could survive the early stages of their evolution without
decaying to a quark star
Possible signatures for strange stars in stellar X-ray binaries
Kilohertz quasi-periodic brightness oscillations (kHz QPOs) observed in
certain X-ray burst sources may represent Keplerian frequencies in the inner
regions of the accretion disk in such systems. If this assumption is strictly
adhered to, we show here that if the central accretor in stellar X-ray burst
sources is a strange star (made up of u, d and s quarks in beta equilibrium,
referred to as strange matter) then the calculated QPO frequencies are
reconcilable with the observed QPO frequencies (corresponding to the highest
frequency of 1.22 kHz, observed so far from the source 4U 1636-53) only for
particular values of the QCD-related parameters which describe the equation of
state of strange matter. We demonstrate that QPO frequencies in the very high
range (1.9-3.1) kHz can be understood in terms of a (non- magnetized) strange
star X-ray binary (SSXB) rather than a neutron star X-ray binary (NSXB). Future
discovery of such high frequency QPOs from X-ray burst sources will constitute
a new astrophysical di- agnostic for identifying solar mass range stable
strange stars in our galaxy.Comment: 4 pages, 2 figs., uses psbox.tex, submitted to A&
Quark matter nucleation in neutron stars and astrophysical implications
A phase of strong interacting matter with deconfined quarks is expected in
the core of massive neutron stars. We investigate the quark deconfinement phase
transition in cold (T = 0) and hot beta-stable hadronic matter. Assuming a
first order phase transition, we calculate and compare the nucleation rate and
the nucleation time due to quantum and thermal nucleation mechanisms. We show
that above a threshold value of the central pressure a pure hadronic star (HS)
(i.e. a compact star with no fraction of deconfined quark matter) is metastable
to the conversion to a quark star (QS) (i.e. a hybrid star or a strange star).
This process liberates an enormous amount of energy, of the order of
10^{53}~erg, which causes a powerful neutrino burst, likely accompanied by
intense gravitational waves emission, and possibly by a second delayed (with
respect to the supernova explosion forming the HS) explosion which could be the
energy source of a powerful gamma-ray burst (GRB). This stellar conversion
process populates the QS branch of compact stars, thus one has in the Universe
two coexisting families of compact stars: pure hadronic stars and quark stars.
We introduce the concept of critical mass M_{cr} for cold HSs and
proto-hadronic stars (PHSs), and the concept of limiting conversion temperature
for PHSs. We show that PHSs with a mass M < M_{cr} could survive the early
stages of their evolution without decaying to QSs. Finally, we discuss the
possible evolutionary paths of proto-hadronic stars.Comment: Invited review paper accepted for publication in EPJ A, Topical Issue
on "Exotic Matter in Neutron Stars
- …