DOCSLIB.ORG

Parametric Studies of Hydrodynamic Instabilities in the Supernova Core by Two- and Three-Dimensional Simulations

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Parametric Studies of Hydrodynamic Instabilities in the Supernova Core by Two- and Three-Dimensional Simulations Max-Planck-Institut fur¨ Astrophysik Parametric Studies of Hydrodynamic Instabilities in the Supernova Core by Two- and Three-Dimensional Simulations Leonhard Scheck Vollst¨andiger Abdruck der von der Fakult¨at fur¨ Physik der Technischen Universit¨at Munchen¨ zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften genehmigten Dissertation. Vorsitzender: Univ.-Prof. Dr. Lothar Oberauer Prufer¨ der Dissertation: 1. Priv.-Doz. Dr. Hans-Thomas Janka 2. Univ.-Prof. Dr. Andrzej J. Buras Die Dissertation wurde am 05.09.2006 bei der Technischen Universit¨at Munchen¨ eingereicht und durch die Fakult¨at fur¨ Physik am 29.11.2006 angenommen. Contents 1 Introduction 5 1.1 The explosion mechanism . 6 1.1.1 Core collapse . 6 1.1.2 Prompt explosions . 7 1.1.3 Delayed explosions . 7 1.2 The anisotropy of core collapse supernovae . 8 1.2.1 Evidence for anisotropy . 8 1.2.2 Possible origins . 9 1.3 Neutron star kicks . 10 1.3.1 The neutron star velocity distribution . 10 1.3.2 Neutron star kick mechanisms . 11 1.4 Aims of this thesis . 12 2 Computational approach and numerical methods 15 2.1 Hydrodynamics and gravity . 15 2.2 Neutrino transport and neutrino source terms . 18 2.3 Numerical grid . 19 2.4 Boundary conditions . 21 2.4.1 Hydrodynamics . 21 2.4.2 Neutrinos . 21 2.4.3 Moving the inner boundary to a different mass shell . 23 3 Explosion anisotropy in two dimensions 25 3.1 Preliminaries . 25 3.1.1 Initial models and initial perturbations . 25 3.1.2 Overview of the simulations . 27 3.1.3 Definitions and approximations for post-processing the simulations . 28 3.2 Two representative models . 34 3.2.1 The character of the flow . 34 3.2.2 Acceleration and recoil of the neutron star . 37 3.2.3 Possible origin of the low-order modes . 40 3.2.4 Comparison with previous works . 41 3.2.5 Sensitivity to the seed perturbations . 44 3.3 Dependence on the initial model and the core luminosity . 47 3.4 The effects of rotation . 49 3.4.1 Evolution of the rotation rate . 50 3.4.2 Morphology . 50 3.4.3 Energetics . 54 3.4.4 Neutron star recoil . 54 3.5 Robustness and long-time evolution of the neutron star recoils . 55 3.5.1 Anisotropic neutrino emission . 55 3 4 Contents 3.5.2 Inertial mass of the neutron star . 56 3.5.3 Neutron star contraction and gravitational potential . 57 3.5.4 Long-time evolution of the neutron star kicks . 58 3.6 Implications for the neutron star velocity distribution . 59 4 The origin of the global anisotropy 63 4.1 Hydrodynamic instabilities . 64 4.1.1 Linear and non-linear convective growth of perturbations . 64 4.1.2 The advective-acoustic cycle . 65 4.2 Simulations . 67 4.2.1 A model without neutrinos . 67 4.2.2 Models with suppressed convection . 70 4.2.3 Models with typical explosion energies . 75 4.3 Interpretation of the linear phase . 76 4.3.1 Measuring oscillation period and cycle efficiency . 76 4.3.2 Identification of the instability mechanism . 79 4.4 Interpretation of the non-linear phase . 82 4.4.1 AAC triggers convection . 82 4.4.2 Explosion vs. non-explosion . 83 4.4.3 The AAC as an alternative to convection . 86 5 Three-dimensional effects 87 5.1 Model parameters . 88 5.1.1 Initial models and boundary conditions . 88 5.1.2 Numerical grid . 88 5.1.3 Additional 2D simulations . 89 5.2 Non-rotating models . 89 5.2.1 Evolution of global quantities . 89 5.2.2 Convective overturn . 94 5.2.3 Neutrino-driven outflows . 100 5.2.4 Global anisotropy and neutron star kicks . 104 5.3 A rotating model . 113 5.3.1 Missing polar downflows . 113 5.3.2 Anisotropic, neutrino-driven outflows . 116 5.3.3 Explosion anisotropy and downflow distribution . 118 5.3.4 Neutron star kick . 122 5.3.5 Spin-kick alignment? . 124 6 Summary and conclusions 127 A Neutrino transport 137 A.1 Transport equation . 137 A.2 Neutrino distribution function . 139 A.3 Optical depth . 140 A.4 Source terms . 142 B Explosion energy 149 C Hydrodynamics in an accelerated frame of reference 155 1 Introduction About two times per century a massive star dies in our Milky Way. Instead of passing away silently, these stars die in spectacular explosions | supernovae. In the first seconds of such an extremely violent event, more energy is set free than was radiated away by the star during its whole life. Only a small part of this energy is released in the form of electromagnetic radiation, but this amount already suffices for the explosion to outshine even its parent galaxy. For this reason supernovae have been noticed since the beginnings of astronomical observations. Reports of strange stars that appear for some time and vanish again can be found in records of Chinese astronomers more than 2000 years ago. Supernova observations appear also in early Korean, Japanese, Arabic and European records. Two of the first \modern" astronomers were fortunate to witness such rare1 events, Tycho Brahe in 1572 and Johannes Kepler in 1604. With the advent of modern astronomical instruments it became possible to study the spectra of supernovae. This allowed Minkowski (1941) to distinguish two classes of supernovae, a clas- sification that is still in use today: The spectra of Type II supernovae show strong Balmer hydrogen lines near maximum brightness, whereas the spectra of Type I supernovae show no signs of hydrogen. The absolute peak magnitude and the shape of the lightcurve also differ for the two classes. Differences in the spectra and the light curve behaviour within the two classes led to subclassifications. The early spectra of Type Ia supernova show lines of silicon, in contrast to types Ib and Ic, which do not. Type Ib and Ic supernovae differ in the presence or absence of helium lines, respectively. The lightcurve of Type II-L supernovae declines linearly after maximum light, whereas Type II-P supernova are characterised by a plateau phase in the light curve. This purely phenomenological classification does not involve any theoretical understanding of the underlying explosion mechanism that could explain the observed differences. A first hint that there are actually two fundamentally different mechanisms at work came from the identification of the environments, in which the supernovae occurred. Type Ia supernovae show no tendency to occur in a certain galaxy type, nor in a certain location within the galaxy. In contrast, Type II, Type Ib, and Type Ic supernovae are observed only in spiral galaxies, and most of them occur in regions with a high star formation rate, i.e., in spiral arms and H II regions. This points 1Only supernovae occurring in the Milky Way could be observed by early astronomers. Using modern instru- ments, nowadays more than 100 supernovae per year are detected in remote galaxies. 5 6 CHAPTER 1. INTRODUCTION to the possibility that the progenitors of Type Ia supernovae are old, low-mass stars and that supernovae of the other classes originate from younger, short-lived, massive stars. Currently the generally agreed upon interpretation is that Type Ia supernovae are thermonuclear explosions of white dwarfs, which do not leave any compact remnant behind. All other types are thought to arise from the collapse of a massive star's core, which triggers an explosion that disrupts the outer layer of the star and leads to the formation of a neutron star or even a black hole. The various subclasses differ in the presence of hydrogen and helium layers at the moment of explosion. The stars can have stripped these outer stellar layers by stellar wind loss or mass transfer in binary star systems. The processes taking place in the first seconds of such a \core collapse supernova", which are still not well-understood, are the subject this work. 1.1 The explosion mechanism In 1934, Baade & Zwicky realized that enormous amounts of gravitational binding energy must be released, when the core of an ordinary star collapses to a neutron star. They suggested that this energy powers the supernova explosion of the dying star. The existence of extremely compact neutron stars had been proposed by Landau only two years before (after the discovery of the neutron by Chadwick in 1932), but such objects were found only some decades later, when periodic radio signals were detected from pulsars, rotating neutron stars with strong magnetic fields. Yet, the process itself, i.e. the mechanism leading to the explosion and the formation of a neutron star, is still not completely understood after more than seventy years of research. 1.1.1 Core collapse There is, however, some agreement about the processes taking place right before the onset of the explosion (see Bethe 1990 for a more detailed description). Near the end of their lives, stars with main sequence masses of more than about 8 M have gone through several burning phases and have developed an onion-shell like structure. For main sequence masses larger than about 56 56 10 M the core of such a progenitor star consists of iron-group elements (mostly Fe and Ni), which are the most tightly bound elements and consequently cannot release further energy by nuclear burning. This core is surrounded by shells of lighter nuclei { around the iron core there is Si/S, and further out O/Ne/Mg, C/O, He, and finally H (the latter two shells may have been lost due to stellar winds or mass transfer in binary systems).
Load more

Recommended publications
  • Neutrino-Driven Explosions in Three Dimensions and Light Curves
    A&A 581, A40 (2015) Astronomy DOI: 10.1051/0004-6361/201425513 & c ESO 2015 Astrophysics Supernova 1987A: neutrino-driven explosions in three dimensions and light curves V. P. Utrobin1;2, A. Wongwathanarat1;3, H.-Th. Janka1, and E. Müller1 1 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany 2 State Scientific Center of the Russian Federation – Institute for Theoretical and Experimental Physics of National Research Center “Kurchatov Institute”, B. Cheremushkinskaya St. 25, 117218 Moscow, Russia e-mail: [email protected] 3 RIKEN, Astrophysical Big Bang Laboratory, 2-1 Hirosawa, Wako, 351-0198 Saitama, Japan Received 13 December 2014 / Accepted 8 June 2015 ABSTRACT Context. The well-observed and well-studied type IIP Supernova 1987A (SN 1987A), produced by the explosion of a blue supergiant in the Large Magellanic Cloud, is a touchstone for the evolution of massive stars, the simulation of neutrino-driven explosions, and the modeling of light curves and spectra. Aims. In the framework of the neutrino-driven explosion mechanism, we study the dependence of explosion properties on the structure of different blue supergiant progenitors and compare the corresponding light curves with observations of SN 1987A. Methods. Three-dimensional (3D) simulations of neutrino-driven explosions are performed with the explicit, finite-volume, Eulerian, multifluid hydrodynamics code Prometheus, using of four available presupernova models as initial data. At a stage of almost homologous expansion, the hydrodynamical and composition variables of the 3D models are mapped to a spherically symmetric configuration, and the simulations are continued with the implicit, Lagrangian radiation-hydrodynamics code Crab to follow the blast-wave evolution into the SN outburst.
    [Show full text]
  • The Rayleigh-Taylor Instability Overturn of Supernova Cores During Bouncing and Resulting Neutrino Energy Release
    THE RAYLEIGH-TAYLOR INSTABILITY OVERTURN OF SUPERNOVA CORES DURING BOUNCING AND RESULTING NEUTRINO ENERGY RELEASE S. A. Colgate and A. G. Petschek University of California, Los Alamos Scientific Laboratory Los Alamos, New Mexico 87545, USA and New Mexico Institute of Mining and Technology Socorro, New Mexico 87801, USA We show that Rayleigh-Taylor convective overturn of the dynamic­ ally formed lepton-trapped core of a supernova is a likely outcome of three sequential events: (1) The bounce or weak reversal shock; (2) the diffusive and convective lepton release from the neutrino- sphere during a fraction of the reversal time (= 100 ms); and (3) the rapid (< 10 ms) Rayleigh-Taylor growth of the £ = 2 mode of an initial rotational perturbation. The overturn releases gravitational energy corresponding to a differential trapped lepton pressure energy of 30 to 50 MeV/nucleon by P dV work in beta equilibrium in a fraction of a millisecond. The resulting kinetic energy of = 7 x 10 ergs is more than adequate to cause the observed supernova emission. Also, the sudden release of = 7 x 10 ergs of ~ 10 MeV neutrinos from the neutrinosphere will cause adequate mass and energy ejection. Patrick A. Wayman fed.), Highlights of Astronomy, Vol. 5, 517-519. Copyright © 1980 by the IAU. Downloaded from https://www.cambridge.org/core. IP address: 170.106.33.42, on 27 Sep 2021 at 17:50:55, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1539299600004408 518 S. A. COLGATE AND A. G. PETSCHEK Mantle L = 2 instability / \ y- Neutrino sphere and circulation Lepton depleted \ Y,SQ2 \ Figure 1 depicts two extreme limits of the fluid flow expected from the unstable overturn of the partially deleptonized neutron star core during formation.
    [Show full text]
  • Transport of Magnetic Fields in Convective, Accreting Supernova
    TRANSPORT OF MAGNETIC FIELDS IN CONVECTIVE, ACCRETING SUPERNOVA CORES Christopher Thompson Physics and Astronomy, University of North Carolina CB3255, Chapel Hill, NC 27599; Canadian Institute for Theoretical Astrophysics, Toronto, ON M5S 3H8 Norman Murray Canadian Institute for Theoretical Astrophysics, Toronto, ON M5S 3H8 ABSTRACT We consider the amplification and transport of a magnetic field in the collapsed core of a massive star, including both the region between the neutrinosphere and the shock, and the central, opaque core. An analytical argument explains why rapid convective overturns persist within a newly formed neutron star for roughly 10 seconds (> 103 overturns), consistent with recent numerical models. A dynamical balance between turbulent and magnetic stresses within this convective layer corresponds to flux densities in excess of 1015G. Material accreting onto the core is heated by neutrinos and also becomes strongly convective. We compare the expected magnetic stresses in this convective ‘gain layer’ with those deep inside the neutron core. Buoyant motions of magnetized fluid are greatly aided by the intense neutrino flux. We calculate the transport rate through a medium containing free neutrons, protons, and electrons, in the limiting cases of degenerate or non-degenerate nucleons. Fields stronger than 1013 G are able to rise ∼ through the outer degenerate layers of the neutron core during the last stages arXiv:astro-ph/0105425v1 24 May 2001 of Kelvin-Helmholtz cooling (up to 10 seconds post-collapse), even though these layers have become stable to convection. We also find the equilibrium shape of a thin magnetic flux rope in the dense hydrostatic atmosphere of the neutron star, along with the critical separation of the footpoints above which the rope undergoes unlimited expansion against gravity.
    [Show full text]
  • How to Blow up a Massive Star
    How to blow up a massive star Müller , B., & Smartt, S. (2017). How to blow up a massive star. Astronomy & Geophysics, 58(2), 2.32-2.37. https://doi.org/10.1093/astrogeo/atx061 Published in: Astronomy & Geophysics Document Version: Publisher's PDF, also known as Version of record Queen's University Belfast - Research Portal: Link to publication record in Queen's University Belfast Research Portal General rights Copyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy The Research Portal is Queen's institutional repository that provides access to Queen's research output. Every effort has been made to ensure that content in the Research Portal does not infringe any person's rights, or applicable UK laws. If you discover content in the Research Portal that you believe breaches copyright or violates any law, please contact [email protected]. Download date:29. Sep. 2021 SUPERNOVAE How to blow up a massive star Bernhard Müller and Stephen Smartt explain how simulations combined with astronomical observations are shaping a more coherent picture of the explosions of massive stars. 1 Supernova remnant SN 1987a in false colour. ALMA data (red) show newly formed dust; Hubble (green) and Chandra (blue) data show where the expanding shock wave meets an outer ring of dust and gas. (ALMA [ESO/NAOJ/NRAO]/A Angelich. Visible: NASA/ESA Hubble.
    [Show full text]
  • The Status of Multi-Dimensional Core-Collapse Supernova Models
    Publications of the Astronomical Society of Australia (PASA), Vol. 33, e048, 29 pages (2016). C Astronomical Society of Australia 2016; published by Cambridge University Press. doi:10.1017/pasa.2016.40 The Status of Multi-Dimensional Core-Collapse Supernova Models B. Muller¨ 1,2,3,4 1Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast, BT7 1NN, UK 2Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, VIC 3800, Australia 3Joint Institute for Nuclear Astrophysics, University of Notre Dame, IN 46556, USA 4Email: [email protected] (Received June 29, 2016; Accepted August 10, 2016) Abstract Models of neutrino-driven core-collapse supernova explosions have matured considerably in recent years. Explosions of low-mass progenitors can routinely be simulated in 1D, 2D, and 3D. Nucleosynthesis calculations indicate that these supernovae could be contributors of some lighter neutron-rich elements beyond iron. The explosion mechanism of more massive stars remains under investigation, although first 3D models of neutrino-driven explosions employing multi-group neutrino transport have become available. Together with earlier 2D models and more simplified 3D simulations, these have elucidated the interplay between neutrino heating and hydrodynamic instabilities in the post-shock region that is essential for shock revival. However, some physical ingredients may still need to be added/improved before simulations can robustly explain supernova explosions over a wide range of progenitors. Solutions recently suggested in the literature include uncertainties in the neutrino rates, rotation, and seed perturbations from convective shell burning. We review the implications of 3D simulations of shell burning in supernova progenitors for the ‘perturbations-aided neutrino-driven mechanism,’ whose efficacy is illustrated by the first successful multi-group neutrino hydrodynamics simulation of an 18 solar mass progenitor with 3D initial conditions.
    [Show full text]
  • UC Office of the President Recent Work
    UC Office of the President Recent Work Title Part IV. Neutrino astrophysics Permalink https://escholarship.org/uc/item/1dc5407d Journal Physics Reports, 227(1-5) ISSN 0370-1573 Author Fuller, GM Publication Date 1993 DOI 10.1016/0370-1573(93)90063-J Peer reviewed eScholarship.org Powered by the California Digital Library University of California PHYSICS REPORTS (Review Section of Physics Letters) 227, Nos. 1—5 (1993) 149—155. PHYSICS REPORTS North-Holland PART IV. NEUTRINO ASTROPHYSICS Supernova dynamics and nucleosynthesis as a probe of closure mass neutrinos George M. Fuller Department of Physics, University of Cal(fornia, San Diego, La Jolla, CA 92093-0319, USA Abstract: we discuss how the neutrino material-heating rate and electron fraction in the region above the neutrino-sphere in a nascent type II supernova become very sensitive to neutrino flavor mixings. Matter-enhancement effects would ensure that a v~or v, (hereafter, v,) neutrino with a vacuum mass ofroughly 10 to 100eV would have a mass-level-crossing with a tight v, in this region. Coincidently, this is the neutrino mass range which is sometimes conjectured to provide the closure density for the universe. Since the supernova v, neutrinos have considerably higher average energies than do the v,, transformations between these species at the level crossings result in more energetic electron neutrinos. This would imply an enhanced Ve capture rate which, in turn, would result in a higher heating rate and would tend to increase the electron fraction, reducing the neutron excess. For a vacuum mixing angle between v, and v~of 0> io~the increase in early heating results in roughly a factor of two increase in supernova explosion energy, which may help solve the explosion-mechanism problem.
    [Show full text]
  • Explosive Nucleosynthesis: Prospects
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server Explosive Nucleosynthesis: Prospects David Arnett a;1, aSteward Observatory, University of Arizona, Tucson AZ 85721, USA Explosive nucleosynthesis is a combination of the nuclear physics of thermonuclear reactions, and the hydrodynamics of the plasma in which the reactions occur. It depends upon the initial conditions— the stellar evolution up to the explosive instability, and the nature of the explosion mechanism. Some key issues for explosive nucleosynthesis are the interaction of burning with hydrodynamics, the degree of microscopic mix- ing in convective zones, and the breaking of spherical symmetry by convection and rotation. Recent experiments on high intensity lasers provides new opportunities for laboratory testing of astro- physical hydrodynamic codes. Implications of supernovae 1987A and 1998bw (GRB980425?), and η Carina are discussed, as well as the formation of black holes or neutron stars. Key words: Nucleosynthesis, Hydrodynamics, Supernovae, Lasers, Black Holes, GRB’s, Rotation, Convection, Jets 1 Introduction This paper is presented to honor David Norman Schramm. It will be a personal view of where this field is going, not a review of work already done, and in a sense it is a formal continuation of many previous discussions Dave and I had on this topic. There is a growing consensus that the synthesis of the elements and their isotopes may be divided into three major components: – Cosmological synthesis of the light elements, – Hydrostatic synthesis in stars, and – Hydrodynamic synthesis in stellar explosions. 1 E-mail: [email protected] Preprint submitted to Elsevier Preprint 17 August 1999 The last item, “explosive nucleosynthesis,” will be the focus here.
    [Show full text]
  • Core Collapse Supernovae — Theory Between Achievements and New Challenges
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server Core Collapse Supernovae — Theory between Achievements and New Challenges H.-Thomas Janka1 1 Max-Planck-Institut f¨ur Astrophysik, Postfach 1523, D–85740 Garching, Germany Abstract. Multi-dimensional hydrodynamic simulations of the post-bounce evolution of collapsed stellar iron cores have demonstrated that convective overturn between the stalled shock and the neutrinosphere can have an important effect on the neutrino-driven explosion mechanism. Whether a model yields a successful explosion or not, however, still depends on the power of neutrino energy deposition behind the stalled shock. The neutrino interaction with the stellar gas in the “hot bubble” also determines the duration of the shock stagnation phase, the explosion energy, and the composition of the neutrino-heated supernova ejecta. More accurate models require a more precise calculation of the neutrino luminosities and spectra and of the angular distributions of the neutrinos in the heating region. Therefore it is necessary to improve the numerical treatment of the neutrino transport, to develop a better understanding of the neutrino opacities of the dense nuclear medium, and to take into account convective processes inside the newly formed neutron star. 1 Convective instabilities — crucial for the explosion? 1.1 First hints from observations Supernova 1987A in the Large Magellanic Cloud, which was the nearest visible type II supernova for more than 380 years, brought a wealth of observational data. The neutrino measurements by the Kamiokande [24], IMB [6] and Baksan [1] laborato- ries confirmed expectations based on theoretical models that neutrinos play a crucial role during the collapse of the stellar core.
    [Show full text]
  • Explosion Mechanism of Core-Collapse Supernovae---A
    Explosion Mechanism of Core-Collapse Supernovae — a View Ten Years after SN 1987A H.-Th. Janka Max-Planck-Institut f¨ur Astrophysik, Karl-Schwarzschild-Str. 1, D-85740 Garching, Germany Abstract. The observation of neutrinos from Supernova 1987A has con- firmed the theoretical conjecture that these particles play a crucial role during the collapse of the core of a massive star. Only one per cent of the energy they carry away from the newly formed neutron star may ac- count for all the kinetic and electromagnetic energy responsible for the spectacular display of the supernova explosion. However, the neutrinos emitted from the collapsed stellar core at the center of the explosion cou- ple so weakly to the surrounding matter that convective processes behind the supernova shock and/or inside the nascent neutron star might be required to increase the efficiency of the energy transfer to the stellar mantle and envelope. The conditions for a successful explosion by the neutrino-heating mechanism and the possible importance of convection in and around the neutron star are shortly reviewed. 1. Introduction Even after ten exciting years SN 1987A keeps rapidly evolving and develops new, unexpected sides like an aging character. In the first few months the historical detection of 24 neutrinos in the underground facilities of the Kamiokande, IMB, and Baksan laboratories caused hectic activity among scientists from very dif- ferent fields. In the subsequent years the scene was dominated by the rise and arXiv:astro-ph/9709013v1 2 Sep 1997 slow decay of light emission in all wavelengths which followed the outbreak of the supernova shock and contained a flood of data about the structure of the progenitor star and the dynamics of the explosion.
    [Show full text]
  • Bethe and Wilson's Delayed Neutrino-Driven Explosion Mechanism Remains the Standard SN Paradigm
    NEUTRINOS PROBE SUPERNOVA DYNAMICS IRENE TAMBORRA GRAPPA Institute, University ofAmsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands In the delayed explosion scenario of a core-collapse supernova (SN), the accretion phase shows pronounced convective overturns and a low-multipole hydrodynamic instability, the so-called standing accretion shock instability (SASI). Neutrino signal variations from the first full­ scale three-dimensional SN simulations with sophisticated neutrino transport are presented as well as their detection perspectives in IceCube and Hyper-Kamiokande. We also discuss a novel neutrino-hydrodynamical instability emerging from these simulations: "Lepton-number Emission Self-sustained Asymmetry" (LESA). LESA most conspicuous manifestation is the lepton-number flux ve minus emission primarily in one hemisphere. ( De) 1 Introduction Bethe and Wilson's delayed neutrino-driven explosion mechanism remains the standard SN paradigm. At core bounce a shock wave forms, it looses all its energy dissociating atoms within the iron shell and is then revived by neutrino heating after 100 ms During the accretion phase, hydrodynamic� instabilities 1. play an important role. These phenom­ ena include convection in the proto-neutron star, large-scale convective overturn below the stalled shock wave, and the standing accretion shock instability (SASI), involving sloshing motions of the 2 shock front as well as spiral modes (see and references therein). We add a new phenomenon to this list: the "Lepton-number Emission Self-sustained Asymmetry" (LESA). LESA most conspic­ uous manifestation is the lepton-number flux (ve minus De) emission primarily in one hemisphere, but it also involves a dipole deformation of the strength of PNS convection and of the large-scale convective overturn below the stalled shock 3.
    [Show full text]
  • Numerical Models of Protoneutron Stars and Type-II Supernovae Recent Developments
    109 CH9700121 Numerical models of protoneutron stars and type-II supernovae recent developments H.-Thomas Janka Max-Planck-Institut fiir Astrophysik Karl-Schwarzschild-Str. 1, D-85740 Garching, Germany- email : thjOmpa-garching.mpg.de ABSTRACT The results of recent multi-dimensional simulations of type-II supernovae are re- viewed. They show that convective instabilities in the collapsed stellar core might play an important role already during the first second after the formation of the supernova shock. Convectively unstable situations occur below and near the neu- trinosphere as well as in the neutrino-heated region between the nascent neutron star and the supernova shock after the latter has stalled at a radius of typically 100-200 km. While convective overturn in the layer of neutrino energy deposition clearly helps the explosion to develop and potentially provides an explanation of strong mantle and envelope mixing, asphericities, and non-uniform 56Ni distribution observed in supernova SN 1987A, its presence and importance depends on the strength of the neutrino heating and thus on the size of the neutrino fluxes from the neutron star. Convection in the hot-bubble region can only develop if the growth timescale of the instabilities and the heating timescale are both shorter than the accretion timescale of the matter advected through the stagnant shock. For too small neutrino luminosities this requirement is not fulfilled and convective activity cannot develop, leading to very weak explosions or even fizzling models, just as in the one-dimensional situation. Convectively enhanced neutrino luminosities from the protoneutron star can therefore provide an essential condition for the explosion of the star.
    [Show full text]
  • Posted 11/13/2015
    –1– 1. The Physics of Nuclear Reaction Rates 1.1. The Four Fundamental Forces in Physics There are four fundamental types of forces in physics. Two act on large scales, gravity and electro-magnetic forces. Gravity is not relevant to nuclear reactions and we ignore it here. The other two act on the scale of the size of atomic nuclei, and have F (1/r2)exp( r/r ), ∝ − 0 where r r . The characteristic value of the constant S, where F S/r2 in the 0 ∼ nuc ∼ appropriate distance range is approximately 1/137 for electro-magnetic reactions, 10−21 for weak nuclear interactions, and 10 for strong nuclear interactions. Typical reaction products for the 3 relevant interactions: e-m forces typically produce photons, reaction is fast, D(p,γ)3He. Weak interactions have very small cross sections and occur very slowly, they typically produce ν, for example H(p, e+ν)D. Strong interactions occur rapidly and produce p, α, n, ..., an example being 3He(3He, 2p)4He. The change in luminosity (energy flux) within the star is dLr = ǫ(nuc)+ ǫ(grav) ǫ(ν) = ǫtotal dMr − ǫ(ν) is negative as neutrinos escape from normal stars without interaction with matter, i.e. without thermalizing; this is not true of very dense compact stars. (Neutrinos will be discussed later, we ignore this term for the moment.) Our goal in this section is to evaluate the terms on the right side of the above equation. In order to have a static star, the above equation must hold at all times.
    [Show full text]