159 research outputs found
A Generalized Solution Method for Parallelized Computation of the Three-dimensional Gravitational Potential on a Multi-patch grid in Spherical Geometry
We present a generalized algorithm based on a spherical harmonics expansion
method for efficient computation of the three-dimensional gravitational
potential on a multi-patch grid in spherical geometry. Instead of solving for
the gravitational potential by superposition of separate contributions from the
mass density distribution on individual grid patch our new algorithm computes
directly the gravitational potential due to contributions from all grid patches
in one computation step, thereby reducing the computational cost of the gravity
solver. This is possible by considering a set of angular weights which are
derived from rotations of spherical harmonics functions defined in a global
coordinate system that is common for all grid patches. Additionally, our
algorithm minimizes data communication between parallel compute tasks by
eliminating its proportionality to the number of subdomains in the grid
configuration, making it suitable for parallelized computation on a multi-patch
grid configuration with any number of subdomains. Test calculations of the
gravitational potential of a tri-axial ellipsoidal body with constant mass
density on the Yin-Yang two-patch overset grid demonstrate that our method
delivers the same level of accuracy as a previous method developed for the
Yin-Yang grid, while offering improved computation efficiency and parallel
scaling behaviour.Comment: 12 pages, 5 figures; accepted for publication in Ap
Three-Dimensional Simulations of Core-Collapse Supernovae: From Shock Revival to Shock Breakout
We present 3D simulations of core-collapse supernovae from blast-wave
initiation by the neutrino-driven mechanism to shock breakout from the stellar
surface, considering two 15 Msun red supergiants (RSG) and two blue supergiants
(BSG) of 15 Msun and 20 Msun. We demonstrate that the metal-rich ejecta in
homologous expansion still carry fingerprints of asymmetries at the beginning
of the explosion, but the final metal distribution is massively affected by the
detailed progenitor structure. The most extended and fastest metal fingers and
clumps are correlated with the biggest and fastest-rising plumes of
neutrino-heated matter, because these plumes most effectively seed the growth
of Rayleigh-Taylor (RT) instabilities at the C+O/He and He/H composition-shell
interfaces after the passage of the SN shock. The extent of radial mixing,
global asymmetry of the metal-rich ejecta, RT-induced fragmentation of initial
plumes to smaller-scale fingers, and maximal Ni and minimal H velocities do not
only depend on the initial asphericity and explosion energy (which determine
the shock and initial Ni velocities) but also on the density profiles and
widths of C+O core and He shell and on the density gradient at the He/H
transition, which lead to unsteady shock propagation and the formation of
reverse shocks. Both RSG explosions retain a great global metal asymmetry with
pronounced clumpiness and substructure, deep penetration of Ni fingers into the
H-envelope (with maximum velocities of 4000-5000 km/s for an explosion energy
around 1.5 bethe) and efficient inward H-mixing. While the 15 Msun BSG shares
these properties (maximum Ni speeds up to ~3500 km/s), the 20 Msun BSG develops
a much more roundish geometry without pronounced metal fingers (maximum Ni
velocities only ~2200 km/s) because of reverse-shock deceleration and
insufficient time for strong RT growth and fragmentation at the He/H interface.Comment: 21 pages, 15 figures; revised version with minor changes in Sect.1;
accepted by Astron. Astrophy
Spatial distribution of radionuclides in 3D models of SN 1987A and Cas A
Fostered by the possibilities of multi-dimensional computational modeling, in
particular the advent of three-dimensional (3D) simulations, our understanding
of the neutrino-driven explosion mechanism of core-collapse supernovae (SNe)
has experienced remarkable progress over the past decade. First
self-consistent, first-principle models have shown successful explosions in 3D,
and even failed cases may be cured by moderate changes of the microphysics
inside the neutron star (NS), better grid resolution, or more detailed
progenitor conditions at the onset of core collapse, in particular large-scale
perturbations in the convective Si and O burning shells. 3D simulations have
also achieved to follow neutrino-driven explosions continuously from the
initiation of the blast wave, through the shock breakout from the progenitor
surface, into the radioactively powered evolution of the SN, and towards the
free expansion phase of the emerging remnant. Here we present results from such
simulations, which form the basis for direct comparisons with observations of
SNe and SN remnants in order to derive constraints on the still disputed
explosion mechanism. It is shown that predictions based on hydrodynamic
instabilities and mixing processes associated with neutrino-driven explosions
yield good agreement with measured NS kicks, light-curve properties of SN
1987A, and asymmetries of iron and 44Ti distributions observed in SN 1987A and
Cassiopeia A.Comment: 9 pages, 6 figures; submitted to: "SN 1987A, 30 years later",
Proceedings IAU Symposium No. 331, 2017; eds. M. Renaud et a
Light curve analysis of ordinary type IIP supernovae based on neutrino-driven explosion simulations in three dimensions
Type II-plateau supernovae (SNe IIP) are the most numerous subclass of
core-collapse SNe originating from massive stars. In the framework of the
neutrino-driven explosion mechanism, we study the SN outburst properties for a
red supergiant progenitor model and compare the corresponding light curves with
observations of the ordinary Type IIP SN 1999em. Three-dimensional (3D)
simulations of (parametrically triggered) neutrino-driven explosions are
performed with the (explicit, finite-volume, Eulerian, multifluid
hydrodynamics) code PROMETHEUS, using a presupernova model of a 15 Msun star as
initial data. At approaching 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 during
the SN outburst. Our 3D neutrino-driven explosion model with an explosion
energy of about 0.5x10^51 erg produces Ni-56 in rough agreement with the amount
deduced from fitting the radioactively powered light-curve tail of SN 1999em.
The considered presupernova model, 3D explosion simulations, and light-curve
calculations can explain the basic observational features of SN 1999em, except
for those connected to the presupernova structure of the outer stellar layers.
Our 3D simulations show that the distribution of Ni-rich matter in velocity
space is asymmetric with a strong dipole component that is consistent with the
observations of SN 1999em. The monotonic luminosity decline from the plateau to
the radioactive tail in ordinary SNe IIP is a manifestation of the intense
turbulent mixing at the He/H composition interface.Comment: 16 pages, 13 figures, 2 tables; added figure, discussions, and
references; accepted for publication in Ap
The infancy of core-collapse supernova remnants
We present 3D hydrodynamic simulations of neutrino-driven supernovae (SNe)
with the PROMETHEUS-HOTB code, evolving the asymmetrically expanding ejecta
from shock breakout until they reach the homologous expansion phase after
roughly one year. Our calculations continue the simulations for two red
supergiant (RSG) and two blue supergiant (BSG) progenitors by Wongwathanarat et
al., who investigated the growth of explosion asymmetries produced by
hydrodynamic instabilities during the first second of the explosion and their
later fragmentation by Rayleigh-Taylor instabilities. We focus on the late time
acceleration and inflation of the ejecta caused by the heating due to the
radioactive decay of Ni to Fe and by a new outward-moving shock,
which forms when the reverse shock from the He/H-shell interface compresses the
central part of the ejecta. The mean velocities of the iron-rich ejecta
increase between 100 km/s and 350 km/s (8-30\%), and the fastest one
percent of the iron accelerates by up to 1000 km/s (20-25\%). This
'Ni-bubble effect', known from 1D models, accelerates the bulk of the nickel in
our 3D models and causes an inflation of the initially overdense Ni-rich
clumps, which leads to underdense, extended fingers, enveloped by overdense
skins of compressed surrounding matter. We also provide volume and surface
filling factors as well as a spherical harmonics analysis to characterize the
spectrum of Ni-clump sizes quantitatively. Three of our four models give volume
filling factors larger than 0.3, consistent with what is suggested for SN 1987A
by observations.Comment: 30 pages, 22 figures, 6 tables, extended discussion of correlation of
late and initial explosion asymmetries, accepted by MNRA
Supernova 1987A: neutrino-driven explosions in three dimensions and light curves
The well-studied type IIP SN 1987A, produced by the explosion of a blue
supergiant (BSG) star, is a touchstone for massive-star evolution, simulations
of neutrino-driven explosions, and modeling of light curves and spectra. In the
framework of the neutrino-driven mechanism, we study the dependence of
explosion properties on the structure of four different BSGs and compare the
corresponding light curves with observations of SN 1987A. We perform 3D
simulations with the PROMETHEUS code until about one day and map the results to
the 1D code CRAB for the light curve calculations. All of our 3D models with
explosion energies compatible with SN 1987A produce 56Ni in rough agreement
with the amount deduced from fitting the radioactively powered light-curve
tail. One of the progenitors yields maximum velocities of ~3000 km/s for the
bulk of ejected 56Ni, consistent with observations. In all of our models inward
mixing of hydrogen during the 3D evolution leads to minimum H-velocities below
100 km/s, in good agreement with spectral observations. The considered BSG
models, 3D explosion simulations, and light-curve calculations can thus explain
basic observational features of SN 1987A. However, all progenitors have too
large pre-SN radii to reproduce the narrow initial luminosity peak, and the
structure of their outer layers is not suitable to match the observed light
curve during the first 30-40 days. Only one stellar model has a structure of
the He core and the He/H composition interface that enables sufficient outward
mixing of 56Ni and inward mixing of hydrogen to produce a good match of the
dome-like shape of the observed light-curve maximum. But this model falls short
of the He-core mass of 6 Msun inferred from the absolute luminosity of the
pre-SN star. The lack of an adequate pre-SN model for SN 1987A is a pressing
challenge for the theory of massive-star evolution. (Abridged)Comment: 18 pages, 11 figures, 4 tables; revised version, accepted by Astron.
Astrophy
SASI Activity in Three-Dimensional Neutrino-Hydrodynamics Simulations of Supernova Cores
The relevance of the standing accretion shock instability (SASI) compared to
neutrino-driven convection in three-dimensional (3D) supernova-core
environments is still highly controversial. Studying a 27 Msun progenitor, we
demonstrate, for the first time, that violent SASI activity can develop in 3D
simulations with detailed neutrino transport despite the presence of
convection. This result was obtained with the Prometheus-Vertex code with the
same sophisticated neutrino treatment so far used only in 1D and 2D models.
While buoyant plumes initially determine the nonradial mass motions in the
postshock layer, bipolar shock sloshing with growing amplitude sets in during a
phase of shock retraction and turns into a violent spiral mode whose growth is
only quenched when the infall of the Si/SiO interface leads to strong shock
expansion in response to a dramatic decrease of the mass accretion rate. In the
phase of large-amplitude SASI sloshing and spiral motions, the postshock layer
exhibits nonradial deformation dominated by the lowest-order spherical
harmonics (l=1, m=0,-1,+1) in distinct contrast to the higher multipole
structures associated with neutrino-driven convection. We find that the SASI
amplitudes, shock asymmetry, and nonradial kinetic energy in 3D can exceed
those of the corresponding 2D case during extended periods of the evolution. We
also perform parametrized 3D simulations of a 25 Msun progenitor, using a
simplified, gray neutrino transport scheme, an axis-free Yin-Yang grid, and
different amplitudes of random seed perturbations. They confirm the importance
of the SASI for another progenitor, its independence of the choice of spherical
grid, and its preferred growth for fast accretion flows connected to small
shock radii and compact proto-neutron stars as previously found in 2D setups.Comment: 17 pages, 10 figures, accepted by The Astrophysical Journa
Induced Rotation in 3D Simulations of Core Collapse Supernovae: Implications for Pulsar Spins
It has been suggested that the observed rotation periods of radio pulsars
might be induced by a non-axisymmetric spiral-mode instability in the turbulent
region behind the stalled supernova bounce shock, even if the progenitor core
was not initially rotating. In this paper, using the three-dimensional AMR code
CASTRO with a realistic progenitor and equation of state and a simple neutrino
heating and cooling scheme, we present a numerical study of the evolution in 3D
of the rotational profile of a supernova core from collapse, through bounce and
shock stagnation, to delayed explosion. By the end of our simulation (420
ms after core bounce), we do not witness significant spin up of the
proto-neutron star core left behind. However, we do see the development before
explosion of strong differential rotation in the turbulent gain region between
the core and stalled shock. Shells in this region acquire high spin rates that
reach Hz, but this region contains too little mass and angular
momentum to translate, even if left behind, into rapid rotation for the full
neutron star. We find also that much of the induced angular momentum is likely
to be ejected in the explosion, and moreover that even if the optimal amount of
induced angular momentum is retained in the core, the resulting spin period is
likely to be quite modest. Nevertheless, induced periods of seconds are
possible.Comment: Accepted to the Astrophysical Journa
Modelling supernova nebular lines in 3D with
We present (EXplosive TRAnsient Spectral Simulator), a
newly developed code aimed at generating 3D spectra for supernovae in the
nebular phase by using modern multi-dimensional explosion models as input. It
is well established that supernovae are asymmetric by nature, and that the
morphology is encoded in the line profiles during the nebular phase, months
after the explosion. In this work, we use to study one such
simulation of a He-core explosion
(, erg)
modelled with the code and evolved to the homologous
phase. Our code calculates the energy deposition from the radioactive decay of
Ni Co Fe and uses this to
determine the Non-Local-Thermodynamic-Equilibrium temperature, excitation and
ionization structure across the nebula. From the physical condition solutions
we generate the emissivities to construct spectra depending on viewing angles.
Our results show large variations in the line profiles with viewing angles, as
diagnosed by the first three moments of the line profiles; shifts, widths, and
skewness. We compare line profiles from different elements, and study the
morphology of line-of-sight slices that determine the flux at each part of a
line profile. We find that excitation conditions can sometimes make the
momentum vector of the ejecta emitting in the excited states significantly
different from that of the bulk of the ejecta of the respective element, thus
giving blueshifted lines for bulk receding material, and vice versa. We compare
the 3.3 He-core model to observations of the Type Ib supernova SN
2007Y.Comment: 20 pages, 15 Figures 2 Tables. Accepted for publication in MNRA
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