2,283 research outputs found
An approach toward the successful supernova explosion by physics of unstable nuclei
We study the explosion mechanism of collapse-driven supernovae by numerical
simulations with a new nuclear EOS based on unstable nuclei. We report new
results of simulations of general relativistic hydrodynamics together with the
Boltzmann neutrino-transport in spherical symmetry. We adopt the new data set
of relativistic EOS and the conventional set of EOS (Lattimer-Swesty EOS) to
examine the influence on dynamics of core-collapse, bounce and shock
propagation. We follow the behavior of stalled shock more than 500 ms after the
bounce and compare the evolutions of supernova core.Comment: 4 pages, 2 figures, contribution to Nuclei in the Cosmos 8, to appear
in Nucl. Phys.
Relativistic Equation of State of Nuclear Matter for Supernova and Neutron Star
We construct the equation of state (EOS) of nuclear matter using the
relativistic mean field (RMF) theory in the wide density, temperature range
with various proton fractions for the use of supernova simulation and the
neutron star calculations. We first construct the EOS of homogeneous nuclear
matter. We use then the Thomas-Fermi approximation to describe inhomogeneous
matter, where heavy nuclei are formed together with free nucleon gas. We
discuss the results on free energy, pressure and entropy in the wide range of
astrophysical interest. As an example, we apply the resulting EOS on the
neutron star properties by using the Oppenheimer-Volkoff equation.Comment: 15 pages, LaTeX, 14 ps-figures, accepted for publication in
Nucl.Phys.
Relativistic Equation of State for Core-Collapse Supernova Simulations
We construct the equation of state (EOS) of dense matter covering a wide
range of temperature, proton fraction, and density for the use of core-collapse
supernova simulations. The study is based on the relativistic mean-field (RMF)
theory, which can provide an excellent description of nuclear matter and finite
nuclei. The Thomas--Fermi approximation in combination with assumed nucleon
distribution functions and a free energy minimization is adopted to describe
the non-uniform matter, which is composed of a lattice of heavy nuclei. We
treat the uniform matter and non-uniform matter consistently using the same RMF
theory. We present two sets of EOS tables, namely EOS2 and EOS3. EOS2 is an
update of our earlier work published in 1998 (EOS1), where only the nucleon
degree of freedom is taken into account. EOS3 includes additional contributions
from hyperons. The effect of hyperons on the EOS is
negligible in the low-temperature and low-density region, whereas it tends to
soften the EOS at high density. In comparison with EOS1, EOS2 and EOS3 have an
improved design of ranges and grids, which covers the temperature range
-- MeV with the logarithmic grid spacing (92 points including T=0), the proton fraction
range --0.65 with the linear grid spacing (66
points), and the density range --
with the logarithmic grid spacing (110 points).Comment: 43 pages, 10 figure
Relativistic Equation of State of Nuclear Matter for Supernova Explosion
We construct the equation of state (EOS) of nuclear matter at finite
temperature and density with various proton fractions within the relativistic
mean field (RMF) theory for the use in the supernova simulations. The
Thomas-Fermi approximation is adopted to describe the non-uniform matter where
we consider nucleus, alpha-particle, proton and neutron in equilibrium. We
treat the uniform matter and non-uniform matter consistently using the RMF
theory. We tabulate the outcome as the pressure, free energy, entropy etc, with
enough mesh points in wide ranges of the temperature, proton fraction, and
baryon mass density.Comment: 22 pages, LaTeX, 9 ps-figures, Submitted to Prog.Theor.Phy
R-Process Nucleosynthesis In Neutrino-Driven Winds From A Typical Neutron Star With M = 1.4 Msun
We study the effects of the outer boundary conditions in neutrino-driven
winds on the r-process nucleosynthesis. We perform numerical simulations of
hydrodynamics of neutrino-driven winds and nuclear reaction network
calculations of the r-process. As an outer boundary condition of hydrodynamic
calculations, we set a pressure upon the outermost layer of the wind, which is
approaching toward the shock wall. Varying the boundary pressure, we obtain
various asymptotic thermal temperature of expanding material in the
neutrino-driven winds for resulting nucleosynthesis. We find that the
asymptotic temperature slightly lower than those used in the previous studies
of the neutrino-driven winds can lead to a successful r-process abundance
pattern, which is in a reasonable agreement with the solar system r-process
abundance pattern even for the typical proto-neutron star mass Mns ~ 1.4 Msun.
A slightly lower asymptotic temperature reduces the charged particle reaction
rates and the resulting amount of seed elements and lead to a high
neutron-to-seed ratio for successful r-process. This is a new idea which is
different from the previous models of neutrino-driven winds from very massive
(Mns ~ 2.0 Msun) and compact (Rns ~ 10 km) neutron star to get a short
expansion time and a high entropy for a successful r-process abundance pattern.
Although such a large mass is sometimes criticized from observational facts on
a neutron star mass, we dissolve this criticism by reconsidering the boundary
condition of the wind. We also explore the relation between the boundary
condition and neutron star mass, which is related to the progenitor mass, for
successful r-process.Comment: 14 pages, 2 figure
Variational Calculation for the Equation of State of Nuclear Matter at Finite Temperatures
An equation of state (EOS) for uniform nuclear matter is constructed at zero
and finite temperatures with the variational method starting from the realistic
nuclear Hamiltonian composed of the Argonne V18 and UIX potentials. The energy
is evaluated in the two-body cluster approximation with the three-body-force
contribution treated phenomenologically so as to reproduce the empirical
saturation conditions. The obtained energies for symmetric nuclear matter and
neutron matter at zero temperature are in fair agreement with those by Akmal,
Pandharipande and Ravenhall, and the maximum mass of the neutron star is 2.2
Msolar. At finite temperatures, a variational method by Schmidt and
Pandharipande is employed to evaluate the free energy, which is used to derive
various thermodynamic quantities of nuclear matter necessary for supernova
simulations. The result of this variational method at finite temperatures is
found to be self-consistent.Comment: Revised Versio
Tables of Hyperonic Matter Equation of State for Core-Collapse Supernovae
We present sets of equation of state (EOS) of nuclear matter including
hyperons using an SU_f(3) extended relativistic mean field (RMF) model with a
wide coverage of density, temperature, and charge fraction for numerical
simulations of core collapse supernovae. Coupling constants of Sigma and Xi
hyperons with the sigma meson are determined to fit the hyperon potential
depths in nuclear matter, U_Sigma(rho_0) ~ +30 MeV and U_Xi(rho_0) ~ -15 MeV,
which are suggested from recent analyses of hyperon production reactions. At
low densities, the EOS of uniform matter is connected with the EOS by Shen et
al., in which formation of finite nuclei is included in the Thomas-Fermi
approximation. In the present EOS, the maximum mass of neutron stars decreases
from 2.17 M_sun (Ne mu) to 1.63 M_sun (NYe mu) when hyperons are included. In a
spherical, adiabatic collapse of a 15 star by the hydrodynamics
without neutrino transfer, hyperon effects are found to be small, since the
temperature and density do not reach the region of hyperon mixture, where the
hyperon fraction is above 1 % (T > 40 MeV or rho_B > 0.4 fm^{-3}).Comment: 23 pages, 6 figures (Fig.3 and related comments on pion potential are
corrected in v3.
Dynamics and neutrino signal of black hole formation in non-rotating failed supernovae. II. progenitor dependence
We study the progenitor dependence of the black hole formation and its
associated neutrino signals from the gravitational collapse of non-rotating
massive stars, following the preceding study on the single progenitor model in
Sumiyoshi et al. (2007). We aim to clarify whether the dynamical evolution
toward the black hole formation occurs in the same manner for different
progenitors and to examine whether the characteristic of neutrino bursts is
general having the short duration and the rapidly increasing average energies.
We perform the numerical simulations by general relativistic neutrino-radiation
hydrodynamics to follow the dynamical evolution from the collapse of
pre-supernova models of 40Msun and 50Msun toward the black hole formation via
contracting proto-neutron stars. For the three progenitor models studied in
this paper, we found that the black hole formation occurs in ~0.4-1.5 s after
core bounce through the increase of proto-neutron star mass together with the
short and energetic neutrino burst. We found that density profile of progenitor
is important to determine the accretion rate onto the proto-neutron star and,
therefore, the duration of neutrino burst. We compare the neutrino bursts of
black hole forming events from different progenitors and discuss whether we can
probe clearly the progenitor and/or the dense matter.Comment: 30 pages, 11 figures, accepted for publication in Ap
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