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Magnetorotational Core-Collapse Supernovae in Three Dimensions  [PDF]
P. M?sta,S. Richers,C. D. Ott,R. Haas,A. L. Piro,K. Boydstun,E. Abdikamalov,C. Reisswig,E. Schnetter
Physics , 2014, DOI: 10.1088/2041-8205/785/2/L29
Abstract: We present results of new three-dimensional (3D) general-relativistic magnetohydrodynamic simulations of rapidly rotating strongly magnetized core collapse. These simulations are the first of their kind and include a microphysical finite-temperature equation of state and a leakage scheme that captures the overall energetics and lepton number exchange due to postbounce neutrino emission. Our results show that the 3D dynamics of magnetorotational core-collapse supernovae are fundamentally different from what was anticipated on the basis of previous simulations in axisymmetry (2D). A strong bipolar jet that develops in a simulation constrained to 2D is crippled by a spiral instability and fizzles in full 3D. While multiple (magneto-)hydrodynamic instabilities may be present, our analysis suggests that the jet is disrupted by an m=1 kink instability of the ultra-strong toroidal field near the rotation axis. Instead of an axially symmetric jet, a completely new, previously unreported flow structure develops. Highly magnetized spiral plasma funnels expelled from the core push out the shock in polar regions, creating wide secularly expanding lobes. We observe no runaway explosion by the end of the full 3D simulation at 185 ms after bounce. At this time, the lobes have reached maximum radii of 900 km.
Numerical modeling of core-collapse supernovae and compact objects  [PDF]
K. Sumiyoshi
Physics , 2012, DOI: 10.1017/S1743921312023186
Abstract: Massive stars (M> 10Msun) end their lives with spectacular explosions due to gravitational collapse. The collapse turns the stars into compact objects such as neutron stars and black holes with the ejection of cosmic rays and heavy elements. Despite the importance of these astrophysical events, the mechanism of supernova explosions has been an unsolved issue in astrophysics. This is because clarification of the supernova dynamics requires the full knowledge of nuclear and neutrino physics at extreme conditions, and large-scale numerical simulations of neutrino radiation hydrodynamics in multi-dimensions. This article is a brief overview of the understanding (with difficulty) of the supernova mechanism through the recent advance of numerical modeling at supercomputing facilities. Numerical studies with the progress of nuclear physics are applied to follow the evolution of compact objects with neutrino emissions in order to reveal the birth of pulsars/black holes from the massive stars.
On the Requirements for Realistic Modeling of Neutrino Transport in Simulations of Core-Collapse Supernovae  [PDF]
Eric J. Lentz,Anthony Mezzacappa,O. E. Bronson Messer,Matthias Liebend?rfer,W. Raphael Hix,Stephen W. Bruenn
Physics , 2011, DOI: 10.1088/0004-637X/747/1/73
Abstract: We have conducted a series of numerical experiments with the spherically symmetric, general relativistic, neutrino radiation hydrodynamics code Agile-BOLTZTRAN to examine the effects of several approximations used in multidimensional core-collapse supernova simulations. Our code permits us to examine the effects of these approximations quantitatively by removing, or substituting for, the pieces of supernova physics of interest. These approximations include: (1) using Newtonian versus general relativistic gravity, hydrodynamics, and transport; (2) using a reduced set of weak interactions, including the omission of non-isoenergetic neutrino scattering, versus the current state-of-the-art; and (3) omitting the velocity-dependent terms, or observer corrections, from the neutrino Boltzmann kinetic equation. We demonstrate that each of these changes has noticeable effects on the outcomes of our simulations. Of these, we find that the omission of observer corrections is particularly detrimental to the potential for neutrino-driven explosions and exhibits a failure to conserve lepton number. Finally, we discuss the impact of these results on our understanding of current, and the requirements for future, multidimensional models.
Neutrino Transfer in Three Dimensions for Core-Collapse Supernovae. I. Static Configurations  [PDF]
Kohsuke Sumiyoshi,Shoichi Yamada
Physics , 2012, DOI: 10.1088/0067-0049/199/1/17
Abstract: We develop a numerical code to calculate the neutrino transfer with multi-energy and multi-angle in three dimensions (3D) for the study of core-collapse supernovae. The numerical code solves the Boltzmann equations for neutrino distributions by the discrete-ordinate (S_n) method with a fully implicit differencing for time advance. The Boltzmann equations are formulated in the inertial frame with collision terms being evaluated to the zeroth order of v/c. A basic set of neutrino reactions for three neutrino species is implemented together with a realistic equation of state of dense matter. The pair process is included approximately in order to keep the system linear. We present numerical results for a set of test problems to demonstrate the ability of the code. The numerical treatments of advection and collision terms are validated first in the diffusion and free streaming limits. Then we compute steady neutrino distributions for a background extracted from a spherically symmetric, general relativistic simulation of 15Msun star and compare them with the results in the latter computation. We also demonstrate multi-D capabilities of the 3D code solving neutrino transfers for artificially deformed supernova cores in 2D and 3D. Formal solutions along neutrino paths are utilized as exact solutions. We plan to apply this code to the 3D neutrino-radiation hydrodynamics simulations of supernovae. This is the first article in a series of reports on the development.
2D and 3D Core-Collapse Supernovae Simulation Results Obtained with the CHIMERA Code  [PDF]
S. W. Bruenn,A. Mezzacappa,W. R. Hix,J. M. Blondin,P. Marronetti,O. E. B. Messer,C. J. Dirk,S. Yoshida
Physics , 2010, DOI: 10.1088/1742-6596/180/1/012018
Abstract: Much progress in realistic modeling of core-collapse supernovae has occurred recently through the availability of multi-teraflop machines and the increasing sophistication of supernova codes. These improvements are enabling simulations with enough realism that the explosion mechanism, long a mystery, may soon be delineated. We briefly describe the CHIMERA code, a supernova code we have developed to simulate core-collapse supernovae in 1, 2, and 3 spatial dimensions. We then describe the results of an ongoing suite of 2D simulations initiated from a 12, 15, 20, and 25 solar mass progenitor. These have all exhibited explosions and are currently in the expanding phase with the shock at between 5,000 and 20,000 km. We also briefly describe an ongoing simulation in 3 spatial dimensions initiated from the 15 solar mass progenitor.
Mechanisms of Core-Collapse Supernovae & Simulation Results from the CHIMERA Code  [PDF]
S. W. Bruenn,A. Mezzacappa,W. R. Hix,J. M. Blondin,P. Marronetti,O. E. B. Messer,C. J. Dirk,S. Yoshida
Physics , 2010, DOI: 10.1063/1.3141615
Abstract: Unraveling the mechanism for core-collapse supernova explosions is an outstanding computational challenge and the problem remains essentially unsolved despite more than four decades of effort. However, much progress in realistic modeling has occurred recently through the availability of multi-teraflop machines and the increasing sophistication of supernova codes. These improvements have led to some key insights which may clarify the picture in the not too distant future. Here we briefly review the current status of the three explosion mechanisms (acoustic, MHD, and neutrino heating) that are currently under active investigation, concentrating on the neutrino heating mechanism as the one most likely responsible for producing explosions from progenitors in the mass range ~10 to ~25 solar masses. We then briefly describe the CHIMERA code, a supernova code we have developed to simulate core-collapse supernovae in 1, 2, and 3 spatial dimensions. We finally describe the results of an ongoing suite of 2D simulations initiated from a 12, 15, 20, and 25 solar mass progenitor. These have all exhibited explosions and are currently in the expanding phase with the shock at between 5,000 and 10,000 km. We finally very briefly describe an ongoing simulation in 3 spatial dimensions initiated from the 15 solar mass progenitor.
Core-Collapse Supernovae, Neutrinos, and Gravitational Waves  [PDF]
C. D. Ott,E. P. O'Connor,S. Gossan,E. Abdikamalov,U. C. T. Gamma,S. Drasco
Physics , 2012, DOI: 10.1016/j.nuclphysbps.2013.04.036
Abstract: Core-collapse supernovae are among the most energetic cosmic cataclysms. They are prodigious emitters of neutrinos and quite likely strong galactic sources of gravitational waves. Observation of both neutrinos and gravitational waves from the next galactic or near extragalactic core-collapse supernova will yield a wealth of information on the explosion mechanism, but also on the structure and angular momentum of the progenitor star, and on aspects of fundamental physics such as the equation of state of nuclear matter at high densities and low entropies. In this contribution to the proceedings of the Neutrino 2012 conference, we summarize recent progress made in the theoretical understanding and modeling of core-collapse supernovae. In this, our emphasis is on multi-dimensional processes involved in the explosion mechanism such as neutrino-driven convection and the standing accretion shock instability. As an example of how supernova neutrinos can be used to probe fundamental physics, we discuss how the rise time of the electron antineutrino flux observed in detectors can be used to probe the neutrino mass hierarchy. Finally, we lay out aspects of the neutrino and gravitational-wave signature of core-collapse supernovae and discuss the power of combined analysis of neutrino and gravitational wave data from the next galactic core-collapse supernova.
Core collapse supernovae and starbursts  [PDF]
Miguel A. Perez-Torres
Physics , 2009,
Abstract: Core-collapse supernovae are the endproducts of massive stars, and yield radio events whose brightness depends on the intensity of the interaction experienced by the supernova ejecta with the circumstellar presupernova wind material. The fact that CCSNe are intrinsically radio supernovae --albeit with a huge range of different radio powers-- and hence unaffected by dust absorption, together with the high resolution and high sensitivity provided by current VLBI arrays, has been exploited to directly image the radio brightness structure of CCSNe in nearby (D <= 20 Mpc) galaxies. This has allowed to gain insight into the physics of both CCSNe and of the circumstellar medium (CSM) with which they interact. In addition, ultra-high-resolution, ultra-high-sensitivity radio observations of CCSNe in Luminous and Ultra-Luminous Infrared Galaxies (LIRGs and ULIRGs, respectively) in the local Universe, can be used to directly measure of the current CCSN rate and star formation rate. In this contribution, I give a brief overview of VLBI observations made of some CCSNe in nearby galaxies, and then present some of the most relevant results obtained with high-resolution radio observations of (U)LIRGs in the local Universe, aimed at directly detecting CCSNe via their radio emission, and thus determine their CCSN and star formation rates, independently of models. This is of particular relevance, in view of the fact that our estimates of star formation (and CCSN) rates in high-z starburst galaxies relies on standard relationships between far-infrared luminosity and star-formation rate. In particular, I will present recently obtained results with the e-EVN on the nuclear region of Arp 299-A.
The Gravitational Wave Signature of Core-Collapse Supernovae  [PDF]
Christian D. Ott
Physics , 2008, DOI: 10.1088/0264-9381/26/6/063001
Abstract: We review the ensemble of anticipated gravitational-wave (GW) emission processes in stellar core collapse and postbounce core-collapse supernova evolution. We discuss recent progress in the modeling of these processes and summarize most recent GW signal estimates. In addition, we present new results on the GW emission from postbounce convective overturn and protoneutron star g-mode pulsations based on axisymmetric radiation-hydrodynamic calculations. Galactic core-collapse supernovae are very rare events, but within 3-5 Mpc from Earth, the rate jumps to 1 in ~2 years. Using the set of currently available theoretical gravitational waveforms, we compute upper-limit optimal signal-to-noise ratios based on current and advanced LIGO/GEO600/VIRGO noise curves for the recent SN 2008bk which exploded at ~3.9 Mpc. While initial LIGOs cannot detect GWs emitted by core-collapse events at such a distance, we find that advanced LIGO-class detectors could put significant upper limits on the GW emission strength for such events. We study the potential occurrence of the various GW emission processes in particular supernova explosion scenarios and argue that the GW signatures of neutrino-driven, magneto-rotational, and acoustically-driven core-collapse SNe may be mutually exclusive. We suggest that even initial LIGOs could distinguish these explosion mechanisms based on the detection (or non-detection) of GWs from a galactic core-collapse supernova.
On the Progenitors of Core-Collapse Supernovae  [PDF]
Douglas C. Leonard
Physics , 2010, DOI: 10.1007/s10509-010-0530-8
Abstract: Theory holds that a star born with an initial mass between about 8 and 140 times the mass of the Sun will end its life through the catastrophic gravitational collapse of its iron core to a neutron star or black hole. This core collapse process is thought to usually be accompanied by the ejection of the star's envelope as a supernova. This established theory is now being tested observationally, with over three dozen core-collapse supernovae having had the properties of their progenitor stars directly measured through the examination of high-resolution images taken prior to the explosion. Here I review what has been learned from these studies and briefly examine the potential impact on stellar evolution theory, the existence of "failed supernovae", and our understanding of the core-collapse explosion mechanism.
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