221 research outputs found
The Equation of State of Neutron-Star Matter in Strong Magnetic Fields
We study the effects of very strong magnetic fields on the equation of state
(EOS) in multicomponent, interacting matter by developing a covariant
description for the inclusion of the anomalous magnetic moments of nucleons.
For the description of neutron star matter, we employ a field-theoretical
approach which permits the study of several models which differ in their
behavior at high density. Effects of Landau quantization in ultra-strong
magnetic fields ( Gauss) lead to a reduction in the electron
chemical potential and a substantial increase in the proton fraction. We find
the generic result for Gauss that the softening of the EOS caused
by Landau quantization is overwhelmed by stiffening due to the incorporation of
the anomalous magnetic moments of the nucleons. In addition, the neutrons
become completely spin polarized. The inclusion of ultra-strong magnetic fields
leads to a dramatic increase in the proton fraction, with consequences for the
direct Urca process and neutron star cooling. The magnetization of the matter
never appears to become very large, as the value of never deviates from
unity by more than a few percent. Our findings have implications for the
structure of neutron stars in the presence of large frozen-in magnetic fields.Comment: 40 pages, 7 figures, accepted for publication in Ap
Thomas-Fermi Calculations of Atoms and Matter in Magnetic Neutron Stars II: Finite Temperature Effects
We present numerical calculations of the equation of state for dense matter
in high magnetic fields, using a temperature dependent Thomas-Fermi theory with
a magnetic field that takes all Landau levels into account. Free energies for
atoms and matter are also calculated as well as profiles of the electron
density as a function of distance from the atomic nucleus for representative
values of the magnetic field strength, total matter density, and temperature.
The Landau shell structure, which is so prominent in cold dense matter in high
magnetic fields, is still clearly present at finite temperature as long as it
is less than approximately one tenth of the cyclotron energy. This structure is
reflected in an oscillatory behaviour of the equation of state and other
thermodynamic properties of dense matter and hence also in profiles of the
density and pressure as functions of depth in the surface layers of magnetic
neutron stars. These oscillations are completely smoothed out by thermal
effects at temperatures of the order of the cyclotron energy or higher.Comment: 37 pages, 17 figures included, submitted to Ap
Correlation energy of an electron gas in strong magnetic fields at high densities
The high-density electron gas in a strong magnetic field B and at zero
temperature is investigated. The quantum strong-field limit is considered in
which only the lowest Landau level is occupied. It is shown that the
perturbation series of the ground-state energy can be represented in analogy to
the Gell-Mann Brueckner expression of the ground-state energy of the field-free
electron gas. The role of the expansion parameter is taken by r_B= (2/3 \pi^2)
(B/m^2) (\hbar r_s /e)^3 instead of the field-free Gell-Mann Brueckner
parameter r_s. The perturbation series is given exactly up to o(r_B) for the
case of a small filling factor for the lowest Landau level.Comment: 10 pages, Accepted for publication in Phys.Rev.
Accretion rate and the occurrence of multi-peaked X-ray bursts
Most Type I X-ray bursts from accreting neutron stars have a lightcurve with
a single peak, but there is a rare population of faint bursts that are double
or even triple peaked. Suggested mechanisms include polar ignition with
equatorial stalling, or multi-step energy release; the latter being caused by
hydrodynamic instabilities or waiting points in the nuclear reaction sequence.
We present an analysis of the accretion rate dependence of the multi-peak
bursts, and discuss the consequences for the various models. The observations
pose particular challenges for the polar ignition mechanism given current
models of ignition latitude dependence.Comment: 5 pages, 4 figures, accepted for publication in A&A Letter
Surface structure of Quark stars with magnetic fields
We investigate the impact of magnetic fields on the electron distribution in
the electrosphere of quark stars. For moderately strong magnetic fields G, quantization effects are generally weak due to the large number
density of electrons at surface, but can nevertheless affect the spectral
features of quark stars. We outline the main observational characteristics of
quark stars as determined by their surface emission, and briefly discuss their
formation in explosive events termed Quark-Novae, which may be connected to the
-process.Comment: 9 pages, 3 figures. Contribution to the proceedings of the IXth
Workshop on High Energy Physics Phenomenology (WHEPP-9), Bhubaneswar, India,
3-14 Jan. 200
Three-Particle Correlations in Simple Liquids
We use video microscopy to follow the phase-space trajectory of a
two-dimensional colloidal model liquid and calculate three-point correlation
functions from the measured particle configurations. Approaching the
fluid-solid transition by increasing the strength of the pair-interaction
potential, one observes the gradual formation of a crystal-like local order due
to triplet correlations, while being still deep inside the fluid phase.
Furthermore, we show that in a strongly interacting system the Born-Green
equation can be satisfied only with the full triplet correlation function but
not with three-body distribution functions obtained from superposing
pair-correlations (Kirkwood superposition approximation).Comment: 4 pages, submitted to PRL, experimental paper, 2nd version: Fig.1 and
two new paragraphs have been adde
Neutrino opacity in magnetised hot and dense nuclear matter
We study the neutrino interaction rates in hot matter at high densities in
the presence of uniform magnetic field. The neutrino cross-sections involving
both the charged current absorption and neutral current scattering reactions on
baryons and leptons have been considered. We have in particular considered the
interesting case when the magnetic field is strong enough to completely
polarise the protons and electrons in supernovae and neutron stars. The opacity
in such a situation is considerably modified and the cross-section develops
anisotropy. This has implications for phenomenon invoked in the literature to
explain the observed pulsar kicks.Comment: 22 latex pages and 7 postscript figure
Dense nuclear matter in a strong magnetic field
We investigate in a relativistic Hartree theory the gross properties of cold
symmetric nuclear matter and nuclear matter in beta equilibrium under the
influence of strong magnetic fields. If the field strengths are above the
critical values for electrons and protons, the respective phase spaces are
strongly modified. This results in additional binding of the systems with
distinctively softer equations of state compared to the field free cases. For
magnetic field Gauss and beyond, the nuclear matter in beta
equilibrium practically converts into a stable proton rich matter.Comment: 13 pages, Revtex, figure include
Hydrogen Phases on the Surface of a Strongly Magnetized Neutron Star
The outermost layers of some neutron stars are likely to be dominated by
hydrogen, as a result of fast gravitational settling of heavier elements. These
layers directly mediate thermal radiation from the stars, and determine the
characteristics of X-ray/EUV spectra. For a neutron star with surface
temperature T\lo 10^6 K and magnetic field B\go 10^{12} G, various forms of
hydrogen can be present in the envelope, including atom, poly-molecules, and
condensed metal. We study the physical properties of different hydrogen phases
on the surface of a strongly magnetized neutron star for a wide range of field
strength and surface temperature . Depending on the values of and
, the outer envelope can be either in a nondegenerate gaseous phase or in a
degenerate metallic phase. For T\go 10^5 K and moderately strong magnetic
field, B\lo 10^{13} G, the envelope is nondegenerate and the surface material
gradually transforms into a degenerate Coulomb plasma as density increases. For
higher field strength, G, there exists a first-order phase
transition from the nondegenerate gaseous phase to the condensed metallic
phase. The column density of saturated vapor above the metallic hydrogen
decreases rapidly as the magnetic field increases or/and temperature decreases.
Thus the thermal radiation can directly emerge from the degenerate metallic
hydrogen surface. The characteristics of surface X-ray/EUV emission for
different phases are discussed. A separate study concerning the possibility of
magnetic field induced nuclear fusion of hydrogen on the neutron star surface
is also presented.Comment: TeX, 35 pages including 6 postscript figures. To be published in Ap
Consistent alpha-cluster description of the 12C (0^+_2) resonance
The near-threshold 12C (0^+_2) resonance provides unique possibility for fast
helium burning in stars, as predicted by Hoyle to explain the observed
abundance of elements in the Universe. Properties of this resonance are
calculated within the framework of the alpha-cluster model whose two-body and
three-body effective potentials are tuned to describe the alpha - alpha
scattering data, the energies of the 0^+_1 and 0^+_2 states, and the
0^+_1-state root-mean-square radius. The extremely small width of the 0^+_2
state, the 0_2^+ to 0_1^+ monopole transition matrix element, and transition
radius are found in remarkable agreement with the experimental data. The
0^+_2-state structure is described as a system of three alpha-particles
oscillating between the ground-state-like configuration and the elongated chain
configuration whose probability exceeds 0.9
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