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 $1/f^\alpha$ ($\alpha:$spectrum exponent) generated by Fourier filtering method. For relatively small $\alpha<\alpha_c(=2)$ time-dependence of mean square displacement (MSD) of the initially localized wavepacket shows ballistic spread and localizes as time elapses. It is shown that $\alpha-$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 $W$. 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 $\alpha$ and $W$.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 ($\sim 100 - 10000M_\odot$). 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 ($\gtrsim 10^5 M_\odot$), 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 $\beta$-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 $300 - 10^4 M_\odot$, 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