3,336 research outputs found
Neutron star properties in the Thomas-Fermi model
The modern nucleon-nucleon interaction of Myers and Swiatecki, adjusted to
the properties of finite nuclei, the parameters of the mass formula, and the
behavior of the optical potential is used to calculate the properties of
--equilibrated neutron star matter, and to study the impact of this
equation of state on the properties of (rapidly rotating) neutron stars and
their cooling behavior. The results are in excellent agreement with the outcome
of calculations performed for a broad collection of sophisticated
nonrelativistic as well as relativistic models for the equation of state.Comment: 23 pages, LaTeX, 15 ps-figure
Quasi Periodic Oscillations in Low Mass X-Ray Binaries and Constraints on the Equation of State of Neutron Star Matter
Recently discovered quasi periodic oscillations in the X-ray brightness of
low mass X-ray binaries are used to derive constraints on the mass of the
neutron star component and the equation of state of neutron star matter. The
observations are compared with models of rapidly rotating neutron stars which
are calculated by means of an exact numerical method in full relativity. For
the equations of state we select a broad collection of models representing
different assumptions about the many-body structure and the complexity of the
composition of super dense matter. The mass constraints differ from their
values in the approximate treatment by \sim 10%. Under the assumption that the
maximum frequency of the quasi periodic oscillations originates from the
innermost stable orbit the mass of the neutron star is in the range: . Especially the quasi periodic oscillation in the
Atoll-source 4U 1820-30 is only consistent with equations of state which are
rather stiff at high densities which is explainable, so far, only with pure
nucleonic/leptonic composition. This interpretation contradicts the hypothesis
that the protoneutron star formed in SN 1987A collapsed to a black hole, since
this would demand a maximum neutron star mass below . The recently
suggested identification of quasi periodic oscillations with frequencies around
10 Hz with the Lense-Thirring precession of the accretion disk is found to be
inconsistent with the models studied in this work, unless it is assumed that
the first overtone of the precession is observed.Comment: 12 pages including figures, to be published in MNRA
Compatibility of neutron star masses and hyperon coupling constants
It is shown that the modern equations of state for neutron star matter based
on microscopic calculations of symmetric and asymmetric nuclear matter are
compatible with the lower bound on the maximum neutron-star mass for a certain
range of hyperon coupling constants, which are constrained by the binding
energies of hyperons in symmetric nuclear matter. The hyperons are included by
means of the relativistic Hartree-- or Hartree--Fock approximation. The
obtained couplings are also in satisfactory agreement with hypernuclei data in
the relativistic Hartree scheme. Within the relativistic Hartree--Fock
approximation hypernuclei have not been investigated so far.Comment: 12 pages, 3 figures. Dedicated to Prof. Georg Suessmann on the
occasion of his 70th birthday. To be published in Zeitschrift fuer
Naturforschung
Symmetric and asymmetric nuclear matter in the relativistic approach at finite temperatures
The properties of hot matter are studied in the frame of the relativistic
Brueckner-Hartree-Fock theory. The equations are solved self-consistently in
the full Dirac space. For the interaction we used the potentials given by
Brockmann and Machleidt. The obtained critical temperatures are smaller than in
most of the nonrelativistic investigations. We also calculated the
thermodynamic properties of hot matter in the relativistic Hartree--Fock
approximation, where the force parameters were adjusted to the outcome of the
relativistic Brueckner--Hartree--Fock calculations at zero temperature. Here,
one obtains higher critical temperatures, which are comparable with other
relativistic calculations in the Hartree scheme.Comment: 8 pages, 9 figures, submitted in a shorter version to Phys. Rev.
Impact of internal heating on the thermal evolution of neutron stars
The impact of various competing heating processes on the thermal evolution of
neutron stars is investigated. We show that internal heating leads to
significantly enhanced surface temperatures for pulsars of middle and old age.
The heating due to thermal creep of pinned vortices and due to outward motion
of proton vortices in the interior of the star leads to a better agreement with
the observed data in the case of enhanced cooling. The strong pinning models
are ruled out by a comparison with the cooling data on the old pulsars. For
millisecond pulsars, the heating due to thermal creep of pinned vortices and
chemical heating of the core have the largest impact on the surface
temperatures. The angular dependence of the heating rates require two
dimensional cooling simulations in general. Such a simulation is performed for
a selected case in order to check the applicability of one-dimensional codes
used in the past.Comment: 18 pages, to be published in A & A. Postscript and additional tables
at http://www.physik.uni-muenchen.de/sektion/suessmann/astro/cool/schaab.109
Energies of Quantum QED Flux Tubes
In this talk I present recent studies on vacuum polarization energies and
energy densities induced by QED flux tubes. I focus on comparing three and four
dimensional scenarios and the discussion of various approximation schemes in
view of the exact treatment.Comment: 9 pages latex, Talk presented at the QFEXT 05 workshop in Barcelona,
Sept. 2005. To appear in the proceeding
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