314 research outputs found
Toward Five-dimensional Core-collapse Supernova Simulations
The computational difficulty of six-dimensional neutrino radiation
hydrodynamics has spawned a variety of approximations, provoking a long history
of uncertainty in the core-collapse supernova explosion mechanism. Under the
auspices of the Terascale Supernova Initiative, we are honoring the physical
complexity of supernovae by meeting the computational challenge head-on,
undertaking the development of a new adaptive mesh refinement code for
self-gravitating, six-dimensional neutrino radiation magnetohydrodynamics. This
code--called {\em GenASiS,} for {\em Gen}eral {\em A}strophysical {\em
Si}mulation {\em S}ystem--is designed for modularity and extensibility of the
physics. Presently in use or under development are capabilities for Newtonian
self-gravity, Newtonian and special relativistic magnetohydrodynamics (with
`realistic' equation of state), and special relativistic energy- and
angle-dependent neutrino transport--including full treatment of the energy and
angle dependence of scattering and pair interactions.Comment: 5 pages. Proceedings of SciDAC 2005, Scientific Discovery through
Advanced Computing, San Francisco, CA, 26-30 June 200
Conservative special relativistic radiative transfer for multidimensional astrophysical simulations: motivation and elaboration
Many astrophysical phenomena exhibit relativistic radiative flows. While
velocities in excess of can occur in these systems, it has been
common practice to approximate radiative transfer to \cO(v/c). In the case of
neutrino transport in core-collapse supernovae, this approximation gives rise
to an inconsistency between the lepton number transfer and lab frame energy
transfer, which have different \cO(v/c) limits. A solution used in
spherically symmetric \cO(v/c) simulations has been to retain, for energy
accounting purposes, the \cO(v^2/c^2) terms in the lab frame energy transfer
equation that arise from the \cO(v/c) neutrino number transport equation.
Avoiding the proliferation of such ``extra'' \cO(v^2/c^2) terms in the
absence of spherical symmetry motivates a special relativistic formalism, which
we exhibit in coordinates sufficiently general to encompass Cartesian,
spherical, and cylindrical coordinate systems.Comment: 9 page
Ascertaining the Core Collapse Supernova Mechanism: An Emerging Picture?
Here we present the results from two sets of simulations, in two and three
spatial dimensions. In two dimensions, the simulations include multifrequency
flux-limited diffusion neutrino transport in the "ray-by-ray-plus"
approximation, two-dimensional self gravity in the Newtonian limit, and nuclear
burning through a 14-isotope alpha network. The three-dimensional simulations
are model simulations constructed to reflect the post stellar core bounce
conditions during neutrino shock reheating at the onset of explosion. They are
hydrodynamics-only models that focus on critical aspects of the shock stability
and dynamics and their impact on the supernova mechanism and explosion. In two
dimensions, we obtain explosions (although in one case weak) for two
progenitors (11 and 15 Solar mass models). Moreover, in both cases the
explosion is initiated when the inner edge of the oxygen layer accretes through
the shock. Thus, the shock is not revived while in the iron core, as previously
discussed in the literature. The three-dimensional studies of the development
of the stationary accretion shock instability (SASI) demonstrate the
fundamentally new dynamics allowed when simulations are performed in three
spatial dimensions. The predominant l=1 SASI mode gives way to a stable m=1
mode, which in turn has significant ramifications for the distribution of
angular momentum in the region between the shock and proto-neutron star and,
ultimately, for the spin of the remnant neutron star. Moreover, the
three-dimensional simulations make clear, given the increased number of degrees
of freedom, that two-dimensional models are severely limited by artificially
imposed symmetries.Comment: 9 pages, 3 figure
Simulation of the Spherically Symmetric Stellar Core Collapse, Bounce, and Postbounce Evolution of a 13 Solar Mass Star with Boltzmann Neutrino Transport, and Its Implications for the Supernova Mechanism
With exact three-flavor Boltzmann neutrino transport, we simulate the stellar
core collapse, bounce, and postbounce evolution of a 13 solar mass star in
spherical symmetry, the Newtonian limit, without invoking convection. In the
absence of convection, prior spherically symmetric models, which implemented
approximations to Boltzmann transport, failed to produce explosions. We are
motivated to consider exact transport to determine if these failures were due
to the transport approximations made and to answer remaining fundamental
questions in supernova theory. The model presented here is the first in a
sequence of models beginning with different progenitors. In this model, a
supernova explosion is not obtained. We discuss the ramifications of our
results for the supernova mechanism.Comment: 5 pages, 3 figures, Submitted to Physical Review Letter
The Innermost Ejecta of Core Collapse Supernovae
We ensure successful explosions (of otherwise non-explosive models) by
enhancing the neutrino luminosity via reducing the neutrino scattering cross
sections or by increasing the heating efficiency via enhancing the neutrino
absorption cross sections in the heating region. Our investigations show that
the resulting electron fraction Ye in the innermost ejecta is close to 0.5, in
some areas even exceeding 0.5. We present the effects of the resulting values
for Ye on the nucleosynthesis yields of the innermost zones of core collapse
supernovae.Comment: 4pages, 2figures; contribution to Nuclei In The Cosmos VIII, to
appear in Nucl. Phys.
Shock Breakout in Core-Collapse Supernovae and its Neutrino Signature
(Abridged) We present results from dynamical models of core-collapse
supernovae in one spatial dimension, employing a newly-developed Boltzmann
neutrino radiation transport algorithm, coupled to Lagrangean hydrodynamics and
a consistent high-density nuclear equation of state. We focus on shock breakout
and its neutrino signature and follow the dynamical evolution of the cores of
11 M_sun, 15 M_sun, and 20 M_sun progenitors through collapse and the first 250
milliseconds after bounce. We examine the effects on the emergent neutrino
spectra, light curves, and mix of species of artificial opacity changes, the
number of energy groups, the weak magnetism/recoil corrections, nucleon-nucleon
bremsstrahlung, neutrino-electron scattering, and the compressibility of
nuclear matter. Furthermore, we present the first high-resolution look at the
angular distribution of the neutrino radiation field both in the
semi-transparent regime and at large radii and explore the accuracy with which
our tangent-ray method tracks the free propagation of a pulse of radiation in a
near vacuum. Finally, we fold the emergent neutrino spectra with the
efficiencies and detection processes for a selection of modern underground
neutrino observatories and argue that the prompt electron-neutrino breakout
burst from the next galactic supernova is in principle observable and usefully
diagnostic of fundamental collapse/supernova behavior. Though we are not in
this study focusing on the supernova mechanism per se, our simulations support
the theoretical conclusion (already reached by others) that spherical (1D)
supernovae do not explode when good physics and transport methods are employed.Comment: 16 emulateapj pages, plus 24 postscript figures, accepted to The
Astrophysical Journal; text revised; neutrino oscillation section expanded;
Fig. 22 correcte
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