Cassiopeia A: Supernova explosion and expansion simulations under strong asymmetry conditions

We propose a model for the explosion of a supernova and the expansion of its ejecta in the presence of a strong initial asymmetry (at the explosion time) in the central part of the star (core) and a possible smallscale asymmetry in the peripheral regions. The Chandra and NuSTAR observations of ejecta in the Cassiopeia A supernova remnant are analyzed. Based on our 1D and 2D numerical simulations performed using the DIANA and NUTCY codes, we propose a model for the explosion and expansion of ejecta that explains the observed experimental data where the materials initially located in the central region of the star end up on the periphery of the cloud of ejecta.     

Simulation of Supernova Expansion

We study the possibility of laboratory modeling of some processes that are intrinsic to supernova (SN) explosion by means of powerful lasers (the so-called laboratory astrophysics); in particular, the possibility of reproducing astrophysical data via numerical models was originally aimed at laser plasma simulation. First of all, we analyze hydrodynamic similarity criteria for the considered processes. Then, we conduct 1D and 2D hydrodynamic simulations to model the expansion dynamics of the SN remnant (the progenitor mass is ～5–15 that of the Sun) during several hundreds of seconds after the explosion, including initially asymmetric configurations. Basing on the similarity criteria, we consider possible laser targets – simulators for a supernova, which mimic some processes inherent in astrophysical phenomenon, such as shock wave propagation through a medium, the development of hydrodynamic instabilities at contact boundaries of shells of different densities, etc. We present a simple solution to the problem of blast wave propagation in a medium with density distributed according to a decreasing power law, which is a good approximation for the density distribution in a supernova progenitor.     

Study of Possibilities of Simulating the Processes of Asymmetric Explosion and Expansion of Supernovae in a Laser Experiment

Processes of explosion and expansion of laser targets, experiments with which could clarify the reason for the observed asymmetric distribution of matter in a remnant cloud of some supernovae (e.g., the Cassiopeia A supernova), have been simulated. By analyzing criteria of hydrodynamic similarity of conditions characteristic of an astrophysical object and experiment, targets for absorbed laser energies in the range of 1–100 kJ have been proposed. This work continues a series of previous studies of supernovae and the possibility of simulating a number of processes observed at the explosion of supernovae such as the motion of a shock wave in matter, development of hydrodynamic instabilities at interfaces between shells with different densities, and largescale mixing of layers of the central region of a star with elements initially located at the periphery of the remnant cloud under laboratory conditions with high-power lasers. The studies are based on the numerical simulation of the explosion and explosion of targets using one- and two-dimensional hydrodynamic programs.     

The astrophysical environment of the solar birthplace

Our Sun, like all stars, formed within a cold molecular cloud. Astronomical observations and theory provide considerable detail into this process. Yet cosmochemical observations of short-lived radionuclides in primitive meteorites, in particular ⁶⁰Fe, provide unequivocal evidence that the early solar system inherited fresh nucleosynthetic material from the core of a hot, massive star, almost certainly ejected in a supernova explosion. I give a short introduction to the fields of star formation and meteoritics and discuss how the reconciliation of their disparate clues to our origin places strong constraints on the environment of the solar birthplace. Direct injection of supernova ejecta into a protoplanetary disc or a dense molecular core is unlikely since their small sizes require placement unusually close to the massive star. Lower density molecular cloud clumps can capture more ejecta but the radionuclides decay during the slow gravitational collapse. The most likely scenario is on the largest scales via the formation of enriched molecular clouds at the intersection of colliding supernova bubbles in spiral arms.     

Pulsar recoil by large-scale anisotropies in supernova explosions

Assuming that the neutrino luminosity from the neutron star core is sufficiently high to drive supernova explosions by the neutrino-heating mechanism, we show that low-mode (l=1,2) convection can develop from random seed perturbations behind the shock. A slow onset of the explosion is crucial, requiring the core luminosity to vary slowly with time, in contrast to the burstlike exponential decay assumed in previous work. Gravitational and hydrodynamic forces by the globally asymmetric supernova ejecta were found to accelerate the remnant neutron star on a time scale of more than a second to velocities above 500 km s(-1), in agreement with observed pulsar proper motions.     

Re-research on the size of proto-neutron star in core-collapse supernova

The electron capture timescale may be shorter than hydrodynamic timescale in inner iron core of core-collapse supernova according to a recent new idea. Based on the new idea, this paper carries out a numerical simulation on supernova explosion for the progenitor model Ws15M. The numerical result shows that the size of proto-neutron star has a significant change （decrease about 20%）, which may affects the propagation of the shock wave and the final explosion energy.     

Modeling Type Ia supernova explosions

Despite their astrophysical significance-as a major contributor to cosmic nucleosynthesis and as distance indicators in observational cosmology-Type Ia supernovae lack theoretical explanation. Not only is the explosion mechanism complex due to the interaction of (potentially turbulent) hydrodynamics and nuclear reactions, but even the initial conditions for the explosion are unknown. Various progenitor scenarios have been proposed. After summarizing some general aspects of Type Ia supernova modeling, recent simulations of our group are discussed. With a sequence of modeling starting (in some cases) from the progenitor evolution and following the explosion hydrodynamics and nucleosynthesis we connect to the formation of the observables through radiation transport in the ejecta cloud. This allows us to analyze several models and to compare their outcomes with observations. While pure deflagrations of Chandrasekhar-mass white dwarfs and violent mergers of two white dwarfs lead to peculiar events (that may, however, find their correspondence in the observed sample of SNe Ia), only delayed detonations in Chandrasekhar-mass white dwarfs or sub-Chandrasekhar-mass explosions remain promising candidates for explaining normal Type Ia supernovae.     

Total energy of the neutrino burst from the supernova 1987A and the mass of the neutron star just born

From the data of the neutrino burst detected by the Kamiokande-II and IMB groups we calculated the total neutrino energy carefully taking into account the efficiency of their water Čerenkov counters. By using this result, we discussed the neutron star mass which was formed by this supernova explosion. We conjectured that the mass is 1.0–1.7M_⊙ and a black hole was not formed, assuming that the distance to the supernova is 50 kpc. If the distance is 56 kpc, the mass range turns into 1.0–1.8M_⊙ and the possibility of black hole formation is also ruled out.     

Most luminous supernovae produced by shocks

The extremely luminous supernova SN2006gy is explained as some other peculiar supernovae: light is produced by a radiative shock propagating in a dense circumstellar envelope. This envelope is formed by a previous weak explosion at a stage of hydrodynamic instability due to creation of electron-positron pairs in stellar interiors. The problems in the theory and observations of supernovae created by multiple explosions are briefly reviewed.     

Notes on hidden mirror world

The extremely luminous supernova SN2006gy is explained as some other peculiar supernovae: light is produced by a radiative shock propagating in a dense circumstellar envelope. This envelope is formed by a previous weak explosion at a stage of hydrodynamic instability due to creation of electron-positron pairs in stellar interiors. The problems in the theory and observations of supernovae created by multiple explosions are briefly reviewed.     

激光聚变内爆流体不稳定性基础问题研究进展

激光聚变有望一劳永逸地解决人类的能源问题,因而受到国际社会的普遍重视,一直是国际研究的前沿热点。目前实现激光惯性约束聚变所面临的最大科学障碍（属于内禀困难）是对内爆过程中高能量密度流体力学不稳定性引起的非线性流动的有效控制,对其研究涵盖高能量密度物理、等离子体物理、流体力学、计算科学、强冲击物理和高压原子物理等多个学科,同时还要具备大规模多物理多尺度多介质流动的数值模拟能力和高功率大型激光装置等研究条件。作为新兴研究课题,高能量密度非线性流动问题充满了各种新奇的现象亟待探索。此外,流体力学不稳定性及其引起的湍流混合,还是天体物理现象（如星系碰撞与合并、恒星演化、原始恒星的形成以及超新星爆炸）中的重要过程,涉及天体物理的一些核心研究内容。本文首先综述了高能量密度非线性流动研究的现状和进展,梳理了其中的挑战和机遇。然后介绍了传统中心点火激光聚变内爆过程发生的主要流体力学不稳定性,在大量分解和综合物理研究基础上,凝练出了目前制约美国国家点火装置（NIF）内爆性能的主要流体不稳定性问题。接下来,总结了国外激光聚变流体不稳定性实验物理的研究概况。最后,展示了内爆物理团队近些年在激光聚变内爆流体不稳定性基础性问题方面的主要研究进展。该团队一直从事激光聚变内爆非线性流动研究与控制,以及聚变靶物理研究与设计,注重理论探索和实验研究相结合,近年来在内爆重要流体力学不稳定性问题的解析理论、数值模拟和激光装置实验设计与数据分析等方面取得了一系列重要成果,有力地推动了该研究方向在国内的发展。     

Type Ia supernovae at high z

Type Ia supernovae are very powerful probes for cosmology and clear tracers of the past history of the universe. Two independent high-redshift supernova collaborations (the High-Z Team and the Supernova Cosmology Project) have presented this year evidence that we live in a low-matter density universe whose expansion is being accelerated by the presence of a dominant vacuum energy density. The Supernova Cosmology Project by using the searches performed at various z for cosmological purposes has measured high-z supernova rates as well. Those measurements provide unvaluable information on the cosmic star formation history, on the efficiency in producing supernovae out of stars, and on the involved timescale to explosion. The cosmic background due to supernova emission can also be calculated in agreement with the measured rates.     

恒星演化和超生爆发理论中某些重要问题的核物理问题

首先,在第1节中我们依次介绍了各种不同质量的恒星演化进程中各个主要热核燃烧的点火条件,致密物质中自由电子系统的简并性对星体热核燃烧的主导作用以及爆炸性核燃烧条件。其次,在第2节中我们讨论了导致恒星核心不稳定坍缩的物理因素和条件。此后,在本第3节中我们评述了Ia型超新星爆发理论尚在急论中的核物理和固体物理的问题。在第4节中我们评述了Ⅱ型（以及Ib型）超新星爆发理论中的严重困难,并且介绍了我们（南京大学研究小组）就超新星中微子延缓爆发机制的关键问题（强大的中微子暴如何产生？）的物理机制提出的具体过程：这中微子暴的强大中微子流量是从刚刚坍缩的高温高密核心通过核物质－－（u,d）夸克系统－－（u,d,s)系统的相变过程在不到1微秒的时间内很快地产生出来的。而且,这个过程导致核心区域的负熵梯度,引起核心区域大规模对流,它将这强大的中微子流量很快地向外输送到中微子球的表面。在第5节中本还介绍了我们就超新星核心高密条件下电荷屏蔽对电子俘获过程的影响所作的探讨研究以及讨论了它对超新星坍缩核心质量（它对超新星瞬时爆发机制成功与否起着关键作用）的可能影响。     

60Fe anomaly in a deep-sea manganese crust and implications for a nearby supernova source

A nearby supernova (SN) explosion in the past can be confirmed by the detection of radioisotopes on Earth that were produced and ejected by the SN. We have now measured a well resolved time profile of the 60Fe concentration in a deep-sea ferromanganese crust and found a highly significant increase 2.8 Myr ago. The amount of 60Fe is compatible with the deposition of ejecta from a SN at a distance of a few 10 pc. The well defined time of the SN explosion makes it possible to search for plausible correlations with other events in Earth's history.     

Spin flip of neutrinos with magnetic moment in core-collapse supernova

Neutrinos with magnetic moment experience chirality flips while scattering off charged particles. It is known that if neutrino is a Dirac fermion, then such chirality flips lead to the production of sterile right-handed neutrinos inside the core of a star during the stellar collapse, which may facilitate the supernova explosion and modify the supernova neutrino signal. In the present paper we reexamine the production of right-handed neutrinos during the collapse using a dynamical model of the collapse. We refine the estimates of the values of the Dirac magnetic moment which are necessary to substantially alter the supernova dynamics and neutrno signal. It is argued in particular that Super-Kamiokande will be sensitive at least to μ _{ν Dirac} = 10⁻¹³μ_B in case of a galactic supernova explosion. Also we briefly discuss the case of Majorana neutrino magnetic moment. It is pointed out that in the inner supernova core spin flips may quickly equilibrate electron neutrinos with nonelectron antineutrinos if μ _{ν Majorana} ≳ 10⁻¹²μ_B. This may lead to various consequences for supernova physics.     

基于强度介质Richtmyer-Meshkov不稳定性理论的微缺陷喷射模型

采用二维多介质欧拉弹塑性流体动力学程序,对金属界面Richtmyer-Meshkov不稳定性和物质喷射进行流体动力学模拟分析,得到强度效应对界面扰动增长和物质喷射的影响特征,揭示扰动增长与物质喷射之间的内在联系.基于理想弹塑性固体界面Richtmyer-Meshkov不稳定性理论,建立强度介质微喷射形成临界判据、喷射总量和最大速度的理论模型.     

Search for supernova-produced 60Fe in a marine sediment

An 60Fe peak in a deep-sea FeMn crust has been interpreted as due to the signature left by the ejecta of a supernova explosion close to the solar system 2.8+/-0.4 Myr ago [Knie, Phys. Rev. Lett. 93, 171103 (2004)10.1103/PhysRevLett.93.171103]. In an attempt to confirm this interpretation with better time resolution and obtain a more direct flux estimate, we measured 60Fe concentrations along a dated marine sediment. We find no 60Fe peak at the expected level from 1.7 to 3.2 Myr ago. Possible causes for the discrepancy are discussed.     

实验室模拟研究超新星遗迹演化动力学过程

文章详细分析讨论了超新星遗迹演化过程中冲击波动力学过程以及激光等离子体喷流的动力学的特点,阐述了利用激光等离子体实验产生与超新星遗迹演化动力学类似的冲击波结构来模拟研究超新星遗迹动力学与演化过程.这些分析与讨论对于实验室利用高能激光模拟研究超新星遗迹演化动力学过程具有重要的意义.     

Laboratory simulations of astrophysical blast waves with high energy lasers

We review recent efforts to simulate aspects of supernova remnants in laboratory experiments by creating energetic explosions with high energy lasers. High energy pulsed lasers are uniquely suited for these kinds of studies. By focusing a laser with pulse energy of a few joules to many hundreds of joules onto a solid target or into a dense gas target, explosive shock waves of very high Mach number can be created. With a well chosen set of laser and target parameters it has been shown by a number of groups that radiative blast waves can be produced. Such blast waves have dynamics dominated by radiation transport and exhibit unusual characteristics, the most important of which include hydrodynamic instabilities which may play an important role in the structure of the interstellar medium. As a result there are now prospects for gaining new insights into astronomical observations of supernova remnants by studying laboratory laser driven plasma systems.