40,521 research outputs found
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
Dynamics and neutrino signal of black hole formation in non-rotating failed supernovae. I. EOS dependence
We study the black hole formation and the neutrino signal from the
gravitational collapse of a non-rotating massive star of 40 Msun. Adopting two
different sets of realistic equation of state (EOS) of dense matter, we perform
the numerical simulations of general relativistic neutrino-radiation
hydrodynamics under the spherical symmetry. We make comparisons of the core
bounce, the shock propagation, the evolution of nascent proto-neutron star and
the resulting re-collapse to black hole to reveal the influence of EOS. We also
explore the influence of EOS on the neutrino emission during the evolution
toward the black hole formation. We find that the speed of contraction of the
nascent proto-neutron star, whose mass increases fast due to the intense
accretion, is different depending on the EOS and the resulting profiles of
density and temperature differ significantly. The black hole formation occurs
at 0.6-1.3 sec after bounce when the proto-neutron star exceeds its maximum
mass, which is crucially determined by the EOS. We find that the average
energies of neutrinos increase after bounce because of rapid temperature
increase, but at different speeds depending on the EOS. The duration of
neutrino emission up to the black hole formation is found different according
to the different timing of re-collapse. These characteristics of neutrino
signatures are distinguishable from those for ordinary proto-neutron stars in
successful core-collapse supernovae. We discuss that a future detection of
neutrinos from black-hole-forming collapse will contribute to reveal the black
hole formation and to constrain the EOS at high density and temperature.Comment: 32 pages, 33 figures, accepted for publication in Ap
Delocalization in One-Dimensional Tight-Binding Models with Fractal Disorder
In the present work, we investigated the correlation-induced
localization-delocalization transition in the one-dimensional tight-binding
model with fractal disorder. We obtained a phase transition diagram from
localized to extended states based on the normalized localization length by
controlling the correlation and the disorder strength of the potential. In
addition, the transition of the diffusive property of wavepacket dynamics is
shown around the critical point.Comment: 9 pages, 11 figure
Wavepacket Dynamics in One-Dimensional System with Long-Range Correlated Disorder
We numerically investigate dynamical property in the one-dimensional
tight-binding model with long-range correlated disorder having power spectrum
(spectrum exponent) generated by Fourier filtering
method. For relatively small time-dependence of mean
square displacement (MSD) of the initially localized wavepacket shows ballistic
spread and localizes as time elapses. It is shown that dependence of
the dynamical localization length (DLL) determined by the MSD exhibits a simple
scaling law in the localization regime for the relatively weak disorder
strength . Furthermore, scaled MSD by the DLL almost obeys an universal
function from the ballistic to the localization regime in the various
combinations of the parameters and .Comment: 4 pages, 4 figure
Numerical Study on Stellar Core Collapse and Neutrino Emission: Probe into the Spherically Symmetric Black Hole Progenitors with 3 - 30Msun Iron Cores
The existence of various anomalous stars, such as the first stars in the
universe or stars produced by stellar mergers, has been recently proposed. Some
of these stars will result in black hole formation. In this study, we
investigate iron core collapse and black hole formation systematically for the
iron-core mass range of 3 - 30Msun, which has not been studied well so far.
Models used here are mostly isentropic iron cores that may be produced in
merged stars in the present universe but we also employ a model that is meant
for a Population III star and is obtained by evolutionary calculation. We solve
numerically the general relativistic hydrodynamics and neutrino transfer
equations simultaneously, treating neutrino reactions in detail under spherical
symmetry. As a result, we find that massive iron cores with ~10Msun
unexpectedly produce a bounce owing to the thermal pressure of nucleons before
black hole formation. The features of neutrino signals emitted from such
massive iron cores differ in time evolution and spectrum from those of ordinary
supernovae. Firstly, the neutronization burst is less remarkable or disappears
completely for more massive models because the density is lower at the bounce.
Secondly, the spectra of neutrinos, except the electron type, are softer owing
to the electron-positron pair creation before the bounce. We also study the
effects of the initial density profile, finding that the larger the initial
density gradient is, the more steeply the neutronization burst declines.
Further more, we suggest a way to probe into the black hole progenitors from
the neutrino emission and estimate the event number for the currently operating
neutrino detectors.Comment: 33 pages, 13 figures, accepted by Ap
Initial Shock Waves for Explosive Nucleosynthesis in Type II Supernova
We have performed 1-dimensional calculations for explosive nucleosynthesis in
collapse-driven supernova and investigated its sensitivity to the initial form
of the shock wave. We have found the tendency that the peak temperature becomes
higher around the mass cut if the input energy is injected more in the form of
kinetic energy rather than internal energy. Then, the mass cut becomes larger,
and, as a result, neutron-rich matter is less included in the ejecta; this is
favorable for producing the observational data compared with a previous model.
Our results imply that the standard method to treat various processes for
stellar evolution, such as convection and electron capture during the silicon
burning stage, are still compatible with the calculation of explosive
nucleosynthesis.Comment: 20 pages, 6 figures, LaTe
Gravitational Collapse and Neutrino Emission of Population III Massive Stars
Pop III stars are the first stars in the universe. They do not contain metals
and their formation and evolution may be different from that of stars of later
generations. In fact, according to the theory of star formation, Pop III stars
might have very massive components (). In this paper,
we compute the spherically symmetric gravitational collapse of these Pop III
massive stars. We solve the general relativistic hydrodynamics and neutrino
transfer equations simultaneously, treating neutrino reactions in detail.
Unlike supermassive stars (), the stars of concern in
this paper become opaque to neutrinos. The collapse is simulated until after an
apparent horizon is formed. We confirm that the neutrino transfer plays a
crucial role in the dynamics of gravitational collapse, and find also that the
-equilibration leads to a somewhat unfamiliar evolution of electron
fraction. Contrary to the naive expectation, the neutrino spectrum does not
become harder for more massive stars. This is mainly because the neutrino
cooling is more efficient and the outer core is more massive as the stellar
mass increases. Here the outer core is the outer part of the iron core falling
supersonically. We also evaluate the flux of relic neutrino from Pop III
massive stars. As expected, the detection of these neutrinos is difficult for
the currently operating detectors. However, if ever observed, the spectrum will
enable us to obtain the information on the formation history of Pop III stars.
We investigate 18 models covering the mass range of ,
making this study the most detailed numerical exploration of spherical
gravitational collapse of Pop III massive stars. This will also serve as an
important foundation for multi-dimensional investigations.Comment: 32 pages, 11 figs, submitted to Ap
Time-reversal Characteristics of Quantum Normal Diffusion
This paper concerns with the time-reversal characteristics of intrinsic
normal diffusion in quantum systems. Time-reversible properties are quantified
by the time-reversal test; the system evolved in the forward direction for a
certain period is time-reversed for the same period after applying a small
perturbation at the reversal time, and the separation between the time-reversed
perturbed and unperturbed states is measured as a function of perturbation
strength, which characterizes sensitivity of the time reversed system to the
perturbation and is called the time-reversal characteristic.
Time-reversal characteristics are investigated for various quantum systems,
namely, classically chaotic quantum systems and disordered systems including
various stochastic diffusion systems. When the system is normally diffusive,
there exists a fundamental quantum unit of perturbation, and all the models
exhibit a universal scaling behavior in the time-reversal dynamics as well as
in the time-reversal characteristics, which leads us to a basic understanding
on the nature of quantum irreversibility.Comment: 21pages, 25figure
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
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