34 research outputs found
Two-Dimensional Core-Collapse Supernova Models with Multi-Dimensional Transport
We present new two-dimensional (2D) axisymmetric neutrino
radiation/hydrodynamic models of core-collapse supernova (CCSN) cores. We use
the CASTRO code, which incorporates truly multi-dimensional, multi-group,
flux-limited diffusion (MGFLD) neutrino transport, including all relevant
terms. Our main motivation for carrying out this study is to
compare with recent 2D models produced by other groups who have obtained
explosions for some progenitor stars and with recent 2D VULCAN results that did
not incorporate terms. We follow the evolution of 12, 15,
20, and 25 solar-mass progenitors to approximately 600 milliseconds after
bounce and do not obtain an explosion in any of these models. Though the reason
for the qualitative disagreement among the groups engaged in CCSN modeling
remains unclear, we speculate that the simplifying ``ray-by-ray' approach
employed by all other groups may be compromising their results. We show that
``ray-by-ray' calculations greatly exaggerate the angular and temporal
variations of the neutrino fluxes, which we argue are better captured by our
multi-dimensional MGFLD approach. On the other hand, our 2D models also make
approximations, making it difficult to draw definitive conclusions concerning
the root of the differences between groups. We discuss some of the diagnostics
often employed in the analyses of CCSN simulations and highlight the intimate
relationship between the various explosion conditions that have been proposed.
Finally, we explore the ingredients that may be missing in current calculations
that may be important in reproducing the properties of the average CCSNe,
should the delayed neutrino-heating mechanism be the correct mechanism of
explosion.Comment: ApJ accepted version. Minor changes from origina
Dimensional Dependence of the Hydrodynamics of Core-Collapse Supernovae
The multidimensional character of the hydrodynamics in core-collapse
supernova (CCSN) cores is a key facilitator of explosions. Unfortunately, much
of this work has necessarily been performed assuming axisymmetry and it remains
unclear whether or not this compromises those results. In this work, we present
analyses of simplified two- and three-dimensional CCSN models with the goal of
comparing the multidimensional hydrodynamics in setups that differ only in
dimension. Not surprisingly, we find many differences between 2D and 3D models.
While some differences are subtle and perhaps not crucial to understanding the
explosion mechanism, others are quite dramatic and make interpreting 2D CCSN
models problematic. In particular, we find that imposing axisymmetry
artificially produces excess power at the largest spatial scales, power that
has been deemed critical in the success of previous explosion models and has
been attributed solely to the standing accretion shock instability.
Nevertheless, our 3D models, which have an order of magnitude less power on
large scales compared to 2D models, explode earlier. Since we see explosions
earlier in 3D than in 2D, the vigorous sloshing associated with the large scale
power in 2D models is either not critical in any dimension or the explosion
mechanism operates differently in 2D and 3D. Possibly related to the earlier
explosions in 3D, we find that about 25% of the accreted material spends more
time in the gain region in 3D than in 2D, being exposed to more integrated
heating and reaching higher peak entropies, an effect we associate with the
differing characters of turbulence in 2D and 3D. Finally, we discuss a simple
model for the runaway growth of buoyant bubbles that is able to quantitatively
account for the growth of the shock radius and predicts a critical luminosity
relation.Comment: Submitted to the Astrophysical Journa
Fornax: a Flexible Code for Multiphysics Astrophysical Simulations
This paper describes the design and implementation of our new multi-group,
multi-dimensional radiation hydrodynamics (RHD) code Fornax and provides a
suite of code tests to validate its application in a wide range of physical
regimes. Instead of focusing exclusively on tests of neutrino radiation
hydrodynamics relevant to the core-collapse supernova problem for which Fornax
is primarily intended, we present here classical and rigorous demonstrations of
code performance relevant to a broad range of multi-dimensional hydrodynamic
and multi-group radiation hydrodynamic problems. Our code solves the
comoving-frame radiation moment equations using the M1 closure, utilizes
conservative high-order reconstruction, employs semi-explicit matter and
radiation transport via a high-order time stepping scheme, and is suitable for
application to a wide range of astrophysical problems. To this end, we first
describe the philosophy, algorithms, and methodologies of Fornax and then
perform numerous stringent code tests, that collectively and vigorously
exercise the code, demonstrate the excellent numerical fidelity with which it
captures the many physical effects of radiation hydrodynamics, and show
excellent strong scaling well above 100k MPI tasks.Comment: Accepted to the Astrophysical Journal Supplement Series; A few more
textual and reference updates; As before, one additional code test include
Electron-Capture and Low-Mass Iron-Core-Collapse Supernovae: New Neutrino-Radiation-Hydrodynamics Simulations
We present new 1D (spherical) and 2D (axisymmetric) simulations of
electron-capture (EC) and low-mass iron-core-collapse supernovae (SN). We
consider six progenitor models: the ECSN progenitor from Nomoto (1984, 1987);
two ECSN-like low-mass low-metallicity iron core progenitors from Heger
(private communication); and the 9-, 10-, and 11- (zero-age main
sequence) progenitors from Sukhbold et al. (2016). We confirm that the ECSN and
ESCN-like progenitors explode easily even in 1D with explosion energies of up
to a 0.15 Bethes (), and are a viable
mechanism for the production of very low-mass neutron stars. However, the 9-,
10-, and 11- progenitors do not explode in 1D and are not even
necessarily easier to explode than higher-mass progenitor stars in 2D. We study
the effect of perturbations and of changes to the microphysics and we find that
relatively small changes can result in qualitatively different outcomes, even
in 1D, for models sufficiently close to the explosion threshold. Finally, we
revisit the impact of convection below the protoneutron star (PNS) surface. We
analyze, 1D and 2D evolutions of PNSs subject to the same boundary conditions.
We find that the impact of PNS convection has been underestimated in previous
studies and could result in an increase of the neutrino luminosity by up to
factors of two.Comment: 18 pages, 17 figures, 3 tables. Major revisions following a fix in
the code input physics. Accepted on Ap