494 research outputs found
Cooling of Hybrid Stars with Spin Down Compression
We study the cooling of hybrid stars coupling with spin-down. Due to the
spin-down of hybrid stars, the interior density continuously increases,
different neutrino reactions may be triggered(from the modified Urca process to
the quark and nucleon direct Urca process) at different stages of evolution. We
calculate the rate of neutrino emissivity of different reactions and simulate
the cooling curves of the rotational hybrid stars. The results show the cooling
curves of hybrid stars clearly depend on magnetic field if the direct urca
reactions occur during the spin-down. Comparing the results of the rotational
star model with the transitional static model, we find the cooling behavior of
rotational model is more complicated, the temperature of star is higher,
especially when direct urca reactions appear in process of rotation. And then
we find that the predicted temperatures of some rotating hybrid stars are
compatible with the pulsar's data which are contradiction with the results of
transitional method.Comment: 8 pages, 5figures, accepted by RA
Gaps below strange star crusts
The gap caused by a strong electric field between the quark surface and
nuclear crust of a strange star is studied in an improved model including
gravity and pressure as well as electrostatic forces. The transition from gap
to crust is followed in detail. The properties of the gap are investigated for
a wide range of parameters assuming both color-flavor locked and non
color-flavor locked strange star cores. The maximally allowed crust density is
generally lower than that of neutron drip. Finite temperature is shown to
increase the gap width, but the effect is significant only at extreme
temperatures. Analytical approximations are derived and shown to provide useful
fits to the numerical results.Comment: 12 pages incl. 14 figures. To appear in Physical Review
The effect of deconfinement phase transition on rotochemical deviations in stars containing mixed phase matter
As a neutron star spins down, its core density increase, changing the
relative equilibrium concentration, and causing deconfinement phase transition
as well. hadron matter are converted into quark matter in the interior, which
enhances the deviation of chemical equilibrium state. We study such deviations
and its chemical energy release.Applying to the simulation of cooling neutron
stars, we find the surface effective temperature of neutron stars is promoted
obviously. This implies that the deconfinement phase transition is able to
raise the chemical heating efficiency
Plasma polarization in high gravity astrophysical objects
Macroscopic plasma polarization, which is created by gravitation and other
mass-acting (inertial) forces in massive astrophysical objects is under
discussion. Non-ideality effect due to strong Coulomb interaction of charged
particles is introduced into consideration as a new source of such
polarization. Simplified situation of totally equilibrium isothermal star
without relativistic effects and influence of magnetic field is considered. The
study is based on variational approach combined with "local density
approximation". It leads to two local forms of thermodynamic equilibrium
conditions: constancy for generalized (electro)chemical potentials and/or
conditions of equilibrium for the forces acting on each charged specie. New
"non-ideality potential" and "non-ideality force" appear naturally in this
consideration. Hypothetical sequences of gravitational, inertial and
non-ideality polarization on thermo- and hydrodynamics of massive astrophysical
objects are under discussion.Comment: 6 pages, no figures, 35 refs, Int. Conference "Physics of Non-Ideal
Plasmas" (PNP-13), Chernogolovka, September 2009, Russi
Signature of deconfinement with spin down compression in cooling hybrid stars
The thermal evolution of neutron stars is coupled to their spin down and the
resulting changes in structure and chemical composition. This coupling
correlates stellar surface temperatures with rotational state as well as time.
We report an extensive investigation of the coupling between spin down and
cooling for hybrid stars which undergo a phase transition to deconfined quark
matter at the high densities present in stars at low rotation frequencies. The
thermal balance of neutron stars is re-analyzed to incorporate phase
transitions and the related latent heat self-consistently, and numerical
calculations are undertaken to simultaneously evolve the stellar structure and
temperature distribution. We find that the changes in stellar structure and
chemical composition with the introduction of a pure quark matter phase in the
core delay the cooling and produce a period of increasing surface temperature
for strongly superfluid stars of strong and intermediate magnetic field
strength. The latent heat of deconfinement is found to reinforce this signature
if quark matter is superfluid and it can dominate the thermal balance during
the formation of a pure quark matter core. At other times it is less important
and does not significantly change the thermal evolution.Comment: 30 pages, 13 figures. Updated to match the version published in Ap
Improved Collective Thomson Scattering measurements of fast ions at ASDEX Upgrade
Understanding the behaviour of the confined fast ions is important in both
current and future fusion experiments. These ions play a key role in heating
the plasma and will be crucial for achieving conditions for burning plasma in
next-step fusion devices. Microwave-based Collective Thomson Scattering (CTS)
is well suited for reactor conditions and offers such an opportunity by
providing measurements of the confined fast-ion distribution function resolved
in space, time and 1D velocity space. We currently operate a CTS system at
ASDEX Upgrade using a gyrotron which generates probing radiation at 105 GHz. A
new setup using two independent receiver systems has enabled improved
subtraction of the background signal, and hence the first accurate
characterization of fast-ion properties. Here we review this new dual-receiver
CTS setup and present results on fast-ion measurements based on the improved
background characterization. These results have been obtained both with and
without NBI heating, and with the measurement volume located close to the
centre of the plasma. The measurements agree quantitatively with predictions of
numerical simulations. Hence, CTS studies of fast-ion dynamics at ASDEX Upgrade
are now feasible. The new background subtraction technique could be important
for the design of CTS systems in other fusion experiments.Comment: 4 pages, 4 figures, to appear in Proc. of "Fusion Reactor
Diagnostics", eds. F. P. Orsitto et al., AIP Conf. Pro
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